Veröffentlichungen
2019 |
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M. Rienäcker, E. L. Warren, M. Schnabel, H. Schulte-Huxel, R. Niepelt, R. Brendel, P. Stradins, A. C. Tamboli, and R. Peibst Back-contacted bottom cells with three terminals: Maximizing power extraction from current-mismatched tandem cells Artikel Forthcoming Progress in Photovoltaics: Research and Applications Forthcoming. Abstract | Links | BibTeX | Schlagwörter: 3T, bipolar junction transistor tandem, bottom cell, current-mismatch, interdigitated back contact cell (IBC), tandem solar cell, three terminal @article{Rienäcker2019,
title = {Back-contacted bottom cells with three terminals: Maximizing power extraction from current-mismatched tandem cells}, author = {M Rienäcker and E L Warren and M Schnabel and H Schulte-Huxel and R Niepelt and R Brendel and P Stradins and A C Tamboli and R Peibst}, doi = {10.1002/pip.3107}, year = {2019}, date = {2019-02-06}, journal = {Progress in Photovoltaics: Research and Applications}, abstract = {Abstract Multi-junction cells can significantly improve the energy yield of photovoltaic systems over a single-junction cell. The internal interconnection scheme of the subcells is an important aspect in determining the resulting levelized cost of electricity. For a dual-junction cell, two approaches are commonly discussed: series-connected tandem cells with two terminals or independently working subcells in a four-terminal (4T) tandem device. In this paper, we explore the working principle and the operation modes of a third, rarely discussed option: a three-terminal (3T) tandem cell using a back-contacted bottom cell with 3Ts. We use current–voltage measurements of illuminated 3T interdigitated back contact cells and confirm that the front and rear base contacts are at similar quasi-Fermi level positions, which enables the bottom cell to either efficiently collect surplus carriers, in the case of a current-limiting or carrier injecting top cell, or inject majority carriers, in the case of a current-limiting bottom cell. As a result, no current matching is needed. The power output of an idealized 3T bottom cell without resistive effects is independent of the current density applied from the top cell. These characteristics of the 3T bottom cells enable a 3T tandem to operate as efficiently as a 4T tandem, while being compatible with monolithic design and not requiring intermediate grids. We propose a simple equivalent circuit model including additional resistive effects, which describes a real 3T bottom cell and achieves excellent agreement to the experiment. We deduce design guidelines for a 3T bottom cell in different operation regimes.}, keywords = {3T, bipolar junction transistor tandem, bottom cell, current-mismatch, interdigitated back contact cell (IBC), tandem solar cell, three terminal}, pubstate = {forthcoming}, tppubtype = {article} } Abstract Multi-junction cells can significantly improve the energy yield of photovoltaic systems over a single-junction cell. The internal interconnection scheme of the subcells is an important aspect in determining the resulting levelized cost of electricity. For a dual-junction cell, two approaches are commonly discussed: series-connected tandem cells with two terminals or independently working subcells in a four-terminal (4T) tandem device. In this paper, we explore the working principle and the operation modes of a third, rarely discussed option: a three-terminal (3T) tandem cell using a back-contacted bottom cell with 3Ts. We use current–voltage measurements of illuminated 3T interdigitated back contact cells and confirm that the front and rear base contacts are at similar quasi-Fermi level positions, which enables the bottom cell to either efficiently collect surplus carriers, in the case of a current-limiting or carrier injecting top cell, or inject majority carriers, in the case of a current-limiting bottom cell. As a result, no current matching is needed. The power output of an idealized 3T bottom cell without resistive effects is independent of the current density applied from the top cell. These characteristics of the 3T bottom cells enable a 3T tandem to operate as efficiently as a 4T tandem, while being compatible with monolithic design and not requiring intermediate grids. We propose a simple equivalent circuit model including additional resistive effects, which describes a real 3T bottom cell and achieves excellent agreement to the experiment. We deduce design guidelines for a 3T bottom cell in different operation regimes.
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C. Hollemann, F. Haase, S. Schäfer, J. Krügener, R. Brendel, and R. Peibst 26.1%-efficient POLO-IBC cells: Quantification of electrical and optical loss mechanisms Artikel Forthcoming Progress in Photovoltaics: Research and Applications Forthcoming. Abstract | Links | BibTeX | Schlagwörter: efficiency potential, IBC solar cells, lifetime monitoring, passivating contacts, POLO @article{Hollemann0000,
title = {26.1%-efficient POLO-IBC cells: Quantification of electrical and optical loss mechanisms}, author = {C Hollemann and F Haase and S Schäfer and J Krügener and R Brendel and R Peibst}, doi = {10.1002/pip.3098}, year = {2019}, date = {2019-01-16}, journal = {Progress in Photovoltaics: Research and Applications}, abstract = {Abstract We present experimental results for interdigitated back contacted (IBC) solar cells with passivating POLO contacts for both polarities with a nominal intrinsic poly-Si region between them. We reach efficiencies of 26.1% and 24.9% on a 1.3 Ω cm and 80 Ω cm p-type FZ wafer and 24.6% on a 2 Ω cm n-type Cz wafer, respectively. The initially measured implied efficiency potentials of the cells after passivating the surfaces are very similar, namely, 26.8%, 26.8%, and 26.4%, respectively. We attribute the difference between the efficiency potential and the final current-voltage measurement to degradation, perimeter, and series and shunt resistance losses, which we quantify by lifetime measurements. With these measurements in combination with a finite element simulation, we determine the surface recombination velocity in the nominal intrinsic poly-Si region to be in the range from 13 to 21 cm s−1. Using the same approach, we analyze the increase of the front surface recombination velocity during cell processing from 2 to 10 cm s−1 for the 1.3 Ω cm and from 0.5 to 2.3 cm s−1 for the 80 Ω cm. This leads to the fact that cells fabricated on lowly doped bulk material are more vulnerable to a process-induced degradation of the surface passivation quality. We further determine the theoretical limits of the cells by firstly idealizing the recombination (28% for 1.3 Ω cm and 28.2% for 80 Ω cm) and secondly also idealizing the optics of the solar cells (29.4% and 29.5%).}, keywords = {efficiency potential, IBC solar cells, lifetime monitoring, passivating contacts, POLO}, pubstate = {forthcoming}, tppubtype = {article} } Abstract We present experimental results for interdigitated back contacted (IBC) solar cells with passivating POLO contacts for both polarities with a nominal intrinsic poly-Si region between them. We reach efficiencies of 26.1% and 24.9% on a 1.3 Ω cm and 80 Ω cm p-type FZ wafer and 24.6% on a 2 Ω cm n-type Cz wafer, respectively. The initially measured implied efficiency potentials of the cells after passivating the surfaces are very similar, namely, 26.8%, 26.8%, and 26.4%, respectively. We attribute the difference between the efficiency potential and the final current-voltage measurement to degradation, perimeter, and series and shunt resistance losses, which we quantify by lifetime measurements. With these measurements in combination with a finite element simulation, we determine the surface recombination velocity in the nominal intrinsic poly-Si region to be in the range from 13 to 21 cm s−1. Using the same approach, we analyze the increase of the front surface recombination velocity during cell processing from 2 to 10 cm s−1 for the 1.3 Ω cm and from 0.5 to 2.3 cm s−1 for the 80 Ω cm. This leads to the fact that cells fabricated on lowly doped bulk material are more vulnerable to a process-induced degradation of the surface passivation quality. We further determine the theoretical limits of the cells by firstly idealizing the recombination (28% for 1.3 Ω cm and 28.2% for 80 Ω cm) and secondly also idealizing the optics of the solar cells (29.4% and 29.5%).
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R. Peibst, M. Rienäcker, B. Min, C. Klamt, R. Niepelt, T. F. Wietler, T. Dullweber, E. Sauter, J. Hübner, M. Oestreich, and R. Brendel IEEE Journal of Photovoltaics 9 (1), 49-54, (2019), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: p-type silicon cell, passivated emitter and rear cells (PERC), passivating contacts, photoluminescence, Photovoltaic cells, Polycrystalline silicon, silicon-based tandem solar cells, solar energy, tunneling junction @article{Peibst2019,
title = {From PERC to Tandem: POLO- and p+/n+ Poly-Si Tunneling Junction as Interface Between Bottom and Top Cell}, author = {R Peibst and M Rienäcker and B Min and C Klamt and R Niepelt and T F Wietler and T Dullweber and E Sauter and J Hübner and M Oestreich and R Brendel}, doi = {10.1109/JPHOTOV.2018.2876999}, issn = {2156-3381}, year = {2019}, date = {2019-01-01}, journal = {IEEE Journal of Photovoltaics}, volume = {9}, number = {1}, pages = {49-54}, abstract = {We present a novel cell concept that combines the tandem cell approach with the passivated emitter and rear cells (PERC) mainstream technology. As an interface between Si bottom and top cell, we utilize passivating n+-type polysilicon on oxide (POLO) contacts and a p+ poly-Si/n+ poly-Si tunneling junction. Our full area PERC+ Si bottom cells are fabricated within a typical industrial process sequence where the POCl$_3$diffusion and SiN$_textx$deposition are replaced by the POLO junction formation processes. The implied open-circuit voltage iV$_textoc$that is measured on these devices reaches up to 708 mV (684 mV) under 1 sun (under filtered spectrum to simulated top cell absorption). On sister cells with planar front side, the respective iV$_textoc$values are 718 mV (696 mV). In order to understand the device physics of our ultra-abrupt p+ poly-Si/n+ poly-Si tunneling junction, we determined the carrier lifetime in the poly-Si by time-resolved photoluminescence. The extracted lifetimes of 42–54 ps enter as input parameter for numerical Sentaurus Device simulations. These simulations reveal the importance of band-to-band and trap-assisted tunneling for a low tunneling junction resistivity of 2.95 mΩ·cm2. Experimentally, an upper limit for the combined junction resistance of the p+ poly-Si/n+ poly-Si/SiO$_textx$stack of 100 mΩ·cm2 is determined.}, keywords = {p-type silicon cell, passivated emitter and rear cells (PERC), passivating contacts, photoluminescence, Photovoltaic cells, Polycrystalline silicon, silicon-based tandem solar cells, solar energy, tunneling junction}, pubstate = {published}, tppubtype = {article} } We present a novel cell concept that combines the tandem cell approach with the passivated emitter and rear cells (PERC) mainstream technology. As an interface between Si bottom and top cell, we utilize passivating n+-type polysilicon on oxide (POLO) contacts and a p+ poly-Si/n+ poly-Si tunneling junction. Our full area PERC+ Si bottom cells are fabricated within a typical industrial process sequence where the POCl$_3$diffusion and SiN$_textx$deposition are replaced by the POLO junction formation processes. The implied open-circuit voltage iV$_textoc$that is measured on these devices reaches up to 708 mV (684 mV) under 1 sun (under filtered spectrum to simulated top cell absorption). On sister cells with planar front side, the respective iV$_textoc$values are 718 mV (696 mV). In order to understand the device physics of our ultra-abrupt p+ poly-Si/n+ poly-Si tunneling junction, we determined the carrier lifetime in the poly-Si by time-resolved photoluminescence. The extracted lifetimes of 42–54 ps enter as input parameter for numerical Sentaurus Device simulations. These simulations reveal the importance of band-to-band and trap-assisted tunneling for a low tunneling junction resistivity of 2.95 mΩ·cm2. Experimentally, an upper limit for the combined junction resistance of the p+ poly-Si/n+ poly-Si/SiO$_textx$stack of 100 mΩ·cm2 is determined.
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T. F. Wietler, B. Min, S. Reiter, Y. Larionova, R. Reineke-Koch, F. Heinemeyer, R. Brendel, A. Feldhoff, J. Krügener, D. Tetzlaff, and R. Peibst IEEE Journal of Photovoltaics 9 (1), 89-96, (2019), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: passivating contacts, POLO junction, Polycrystalline silicon, thermal treatment, ZnO:Al @article{Wietler2019,
title = {High Temperature Annealing of ZnO:Al on Passivating POLO Junctions: Impact on Transparency, Conductivity, Junction Passivation, and Interface Stability}, author = {T F Wietler and B Min and S Reiter and Y Larionova and R Reineke-Koch and F Heinemeyer and R Brendel and A Feldhoff and J Krügener and D Tetzlaff and R Peibst}, doi = {10.1109/JPHOTOV.2018.2878337}, issn = {2156-3381}, year = {2019}, date = {2019-01-01}, journal = {IEEE Journal of Photovoltaics}, volume = {9}, number = {1}, pages = {89-96}, abstract = {We investigate the enhancement in transparency and conductivity of aluminum doped zinc oxide (ZnO:Al) layers upon high-temperature annealing and its impact on contact resistance, as well as, on passivation properties of carrier selective junctions based on doped polycrystalline Si on a passivating silicon oxide (POLO). The temperature stability of these junctions allows annealing of the ZnO:Al/POLO combination up to 600 °C. We prepare ZnO:Al films by dc magnetron sputtering at room temperature. We determine the complex refractive index of ZnO:Al in dependence of post-deposition annealing (PDA) temperature by spectroscopic ellipsometry. High-temperature annealing improves the conductivity and reduces the absorption within ZnO:Al. The optical losses in a ZnO:Al/POLO stack are rather limited by the poly-Si layer than by the ZnO:Al. The sheet resistance improves from roughly 20 000 Ω/sq for 80 nm thick as-deposited ZnO:Al films to 72 Ω/sq after fast firing at 600 °C. At the same time, PDA cures the damage induced in the POLO junctions during ZnO:Al deposition. After PDA with Al$_textx$O$_texty$capping layers, the passivation quality even surpasses the initial level. A transmission electron microscopy analysis of the interface between the ZnO:Al and the underlying poly-Si reveals the formation of a silicon oxide like interfacial layer after PDA at 400 °C. This interfacial layer causes a high contact resistivity of the metal/ZnO:Al/POLO-junction and could limit the thermal budget for cell processing. Our results indicate that after successful process adjustment, ZnO:Al could substitute In-based transparent conductive oxides on POLO cells for cost reasons, as well as, enable a high efficiency potential.}, keywords = {passivating contacts, POLO junction, Polycrystalline silicon, thermal treatment, ZnO:Al}, pubstate = {published}, tppubtype = {article} } We investigate the enhancement in transparency and conductivity of aluminum doped zinc oxide (ZnO:Al) layers upon high-temperature annealing and its impact on contact resistance, as well as, on passivation properties of carrier selective junctions based on doped polycrystalline Si on a passivating silicon oxide (POLO). The temperature stability of these junctions allows annealing of the ZnO:Al/POLO combination up to 600 °C. We prepare ZnO:Al films by dc magnetron sputtering at room temperature. We determine the complex refractive index of ZnO:Al in dependence of post-deposition annealing (PDA) temperature by spectroscopic ellipsometry. High-temperature annealing improves the conductivity and reduces the absorption within ZnO:Al. The optical losses in a ZnO:Al/POLO stack are rather limited by the poly-Si layer than by the ZnO:Al. The sheet resistance improves from roughly 20 000 Ω/sq for 80 nm thick as-deposited ZnO:Al films to 72 Ω/sq after fast firing at 600 °C. At the same time, PDA cures the damage induced in the POLO junctions during ZnO:Al deposition. After PDA with Al$_textx$O$_texty$capping layers, the passivation quality even surpasses the initial level. A transmission electron microscopy analysis of the interface between the ZnO:Al and the underlying poly-Si reveals the formation of a silicon oxide like interfacial layer after PDA at 400 °C. This interfacial layer causes a high contact resistivity of the metal/ZnO:Al/POLO-junction and could limit the thermal budget for cell processing. Our results indicate that after successful process adjustment, ZnO:Al could substitute In-based transparent conductive oxides on POLO cells for cost reasons, as well as, enable a high efficiency potential.
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2018 |
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V. Titova, and J. Schmidt Implementation of full-area-deposited electron-selective TiOx layers into silicon solar cells Artikel AIP Advances 8 (12), 125023, (2018). Abstract | Links | BibTeX | Schlagwörter: atomic layer deposition, Electrical properties and parameters, Internal quantum efficiency, passivation, Solar Cells, Transition metal oxides, Work functions @article{Titova2018c,
title = {Implementation of full-area-deposited electron-selective TiOx layers into silicon solar cells}, author = {V Titova and J Schmidt}, doi = {10.1063/1.5061924}, year = {2018}, date = {2018-12-26}, journal = {AIP Advances}, volume = {8}, number = {12}, pages = {125023}, abstract = {We examine two different silicon solar cell designs featuring full-area electron-selective contacts based on ultrathin (2–3 nm) titanium oxide (TiOx) films deposited by atomic layer deposition. The first cell design applies a layer stack to the cell front, which is composed of an ultrathin intrinsic amorphous silicon (i-a-Si:H) layer for interface passivation, the TiOx film and an indium tin oxide (ITO) layer to provide a good lateral conductance for electrons to the metal fingers. Whereas carrier lifetime measurements on test structures promise high implied open-circuit voltages Voc up to 726 mV, the realized solar cells achieve disappointingly low Voc values <400 mV. The J-V parameters of this cell type are negatively affected by a reverse diode occurring due to the contacting of the TiOx by the high-work function ITO layer. In the second cell type, we implement a layer stack to the cell rear, which is composed of an ultrathin silicon oxide (SiOy) layer, the TiOx film and a full-area-deposited aluminum (Al) layer. Initial Voc values of these cells are relatively low (<600 mV), but improve significantly after annealing at 350°C. The best cell featuring a SiOy/TiOx/Al rear contact achieves an open-circuit voltage of 661 mV and an efficiency of 20.3%. No reverse diode is observed, which is attributed to the lower work function of the Al compared to ITO in the first cell design. From internal quantum efficiency measurements, we extract a rear surface recombination velocity Srear of (52±20) cm/s for our best cell, which is well compatible with efficiencies exceeding 23%.}, keywords = {atomic layer deposition, Electrical properties and parameters, Internal quantum efficiency, passivation, Solar Cells, Transition metal oxides, Work functions}, pubstate = {published}, tppubtype = {article} } We examine two different silicon solar cell designs featuring full-area electron-selective contacts based on ultrathin (2–3 nm) titanium oxide (TiOx) films deposited by atomic layer deposition. The first cell design applies a layer stack to the cell front, which is composed of an ultrathin intrinsic amorphous silicon (i-a-Si:H) layer for interface passivation, the TiOx film and an indium tin oxide (ITO) layer to provide a good lateral conductance for electrons to the metal fingers. Whereas carrier lifetime measurements on test structures promise high implied open-circuit voltages Voc up to 726 mV, the realized solar cells achieve disappointingly low Voc values <400 mV. The J-V parameters of this cell type are negatively affected by a reverse diode occurring due to the contacting of the TiOx by the high-work function ITO layer. In the second cell type, we implement a layer stack to the cell rear, which is composed of an ultrathin silicon oxide (SiOy) layer, the TiOx film and a full-area-deposited aluminum (Al) layer. Initial Voc values of these cells are relatively low (<600 mV), but improve significantly after annealing at 350°C. The best cell featuring a SiOy/TiOx/Al rear contact achieves an open-circuit voltage of 661 mV and an efficiency of 20.3%. No reverse diode is observed, which is attributed to the lower work function of the Al compared to ITO in the first cell design. From internal quantum efficiency measurements, we extract a rear surface recombination velocity Srear of (52±20) cm/s for our best cell, which is well compatible with efficiencies exceeding 23%.
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J. Schmidt, R. Peibst, and R. Brendel Surface passivation of crystalline silicon solar cells: Present and future Artikel Solar Energy Materials and Solar Cells 187 , 39-54, (2018), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: Carrier-selective contacts, silicon solar cells, surface passivation @article{Schmidt2018b,
title = {Surface passivation of crystalline silicon solar cells: Present and future}, author = {J Schmidt and R Peibst and R Brendel}, doi = {10.1016/j.solmat.2018.06.047}, issn = {0927-0248}, year = {2018}, date = {2018-12-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {187}, pages = {39-54}, abstract = {In the first part of this paper, we review the developments which led to the present state-of-the-art in the surface passivation of today's industrially predominant dopant-diffused crystalline silicon (c-Si) solar cells, based on dielectric layers such as silicon oxide, silicon nitride, aluminum oxide and stacks thereof. In the second part of this review, we focus on the future developments in the field of c-Si solar cells based on carrier-selective passivation layers. Whereas the dielectric layers are insulating and are hence applied only for passivating the non-contacted areas of the silicon surface, the carrier-selective passivation layers are intended to provide an effective passivation of non-contacted as well as contacted areas of a c-Si solar cell, thereby increasing the efficiency potential of c-Si solar cells significantly. Due to the fact that the carrier-selective layers are implemented in a contact, besides the good passivation properties for minorities, these layers must also provide a good majority carrier transport, i.e. they have to provide a low contact resistance. Both properties, i.e. suppression of minority-carrier recombination as well as good majority-carrier transport, define the selectivity of the carrier-selective contact, which is an important figure of merit for the assessment and comparison of different types of carrier-selective contacts. One very promising type of carrier-selective passivation layer is based on heavily doped polycrystalline silicon layers deposited on a thin silicon oxide layer, the latter providing the excellent passivation while enabling efficient majority-carrier transport via pin-holes and/or tunneling. Moreover, we discuss metal oxides and conductive polymers, which have only recently been applied to c-Si photovoltaics, but seem to have a promising potential as low-cost selective contact materials. We finally compare combinations of the various options of carrier-selective layers concerning their combined selectivities and efficiency potentials.}, keywords = {Carrier-selective contacts, silicon solar cells, surface passivation}, pubstate = {published}, tppubtype = {article} } In the first part of this paper, we review the developments which led to the present state-of-the-art in the surface passivation of today's industrially predominant dopant-diffused crystalline silicon (c-Si) solar cells, based on dielectric layers such as silicon oxide, silicon nitride, aluminum oxide and stacks thereof. In the second part of this review, we focus on the future developments in the field of c-Si solar cells based on carrier-selective passivation layers. Whereas the dielectric layers are insulating and are hence applied only for passivating the non-contacted areas of the silicon surface, the carrier-selective passivation layers are intended to provide an effective passivation of non-contacted as well as contacted areas of a c-Si solar cell, thereby increasing the efficiency potential of c-Si solar cells significantly. Due to the fact that the carrier-selective layers are implemented in a contact, besides the good passivation properties for minorities, these layers must also provide a good majority carrier transport, i.e. they have to provide a low contact resistance. Both properties, i.e. suppression of minority-carrier recombination as well as good majority-carrier transport, define the selectivity of the carrier-selective contact, which is an important figure of merit for the assessment and comparison of different types of carrier-selective contacts. One very promising type of carrier-selective passivation layer is based on heavily doped polycrystalline silicon layers deposited on a thin silicon oxide layer, the latter providing the excellent passivation while enabling efficient majority-carrier transport via pin-holes and/or tunneling. Moreover, we discuss metal oxides and conductive polymers, which have only recently been applied to c-Si photovoltaics, but seem to have a promising potential as low-cost selective contact materials. We finally compare combinations of the various options of carrier-selective layers concerning their combined selectivities and efficiency potentials.
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T. Dullweber, and J. Schmidt Surface passivation of industrial PERC solar cells Buchkapitel J. John (Hrsg.): Surface Passivation of Industrial Crystalline Silicon Solar Cells, Kapitel 8, 95-116, Institution of Engineering and Technology, (2018), ISBN: 978-1-78561-246-6. BibTeX | Schlagwörter: passivation @inbook{Dullweber2018b,
title = {Surface passivation of industrial PERC solar cells}, author = {T Dullweber and J Schmidt}, editor = {J John}, isbn = {978-1-78561-246-6}, year = {2018}, date = {2018-11-30}, booktitle = {Surface Passivation of Industrial Crystalline Silicon Solar Cells}, pages = {95-116}, publisher = {Institution of Engineering and Technology}, chapter = {8}, keywords = {passivation}, pubstate = {published}, tppubtype = {inbook} } |
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F. Kiefer, N. Wehmeier, T. Brendemühl, L. Mettner, F. Haase, M. Holthausen, C. Daeschlein, O. Wunnicke, C. Mader, and S. Kajari-Schröder Inkjet Printing as a New Method for the Preparation of POLO Contacts Vortrag Boston, MA, USA, 28.11.2018, (2018 MRS Fall Meeting & Exhibit). Abstract | BibTeX | Schlagwörter: POLO @misc{Kiefer2018,
title = {Inkjet Printing as a New Method for the Preparation of POLO Contacts}, author = {F Kiefer and N Wehmeier and T Brendemühl and L Mettner and F Haase and M Holthausen and C Daeschlein and O Wunnicke and C Mader and S Kajari-Schröder }, year = {2018}, date = {2018-11-28}, address = {Boston, MA, USA}, abstract = {The increase of Si solar cell efficiencies in the last years have been mainly driven by passivating contacts, either with amorphous Si (heterostructure with intrinsic thin layer, HIT) or silicon oxide (poly-Si on oxide, POLO; tunnel oxide passivating contact, TopCon) as an interface layer [1-3]. Interdigitated back-contact (IBC) solar cells have demonstrated the highest efficiencies of more than 26 % [4,5], as they combine a high voltage resulting from the passivating contacts and a higher current compared to front-contacted solar cells due to the absence of metal shading. A drawback shared by all presented techniques for the deposition of POLO contacts so far is that they cover the full area of one or both sides of the wafer [6]. During the process of an IBC Si solar cell, a structuring of the deposited poly-Si layer is necessary. To overcome these hurdles, Evonik developed an inkjet printable, doped precursor (Evonik’s liquid silicon) which can be used for the direct generation of structured amorphous and polycrystalline Si layers [7,8]. As direct printing on silicon oxide layers used for POLO junctions is possible, this is a novel, unique possibility to prepare in-situ doped and in-situ structured poly-Si layers with only three process steps: Printing of the liquid Si ink onto the wafer under inert atmosphere with an inkjet printer – conversion of the liquid Si into amorphous Si on a hotplate – annealing of the layer stack in a tube furnace with break-up of the silicon oxide and conversion of the amorphous Si into poly-Si. The shape of the printed Si layer can be designed freely, the minimum structure size of the printed POLO contact is limited only by the drop size of the inkjet process. In this work, we present the preparation and properties of phosphorous-doped inkjet-printed POLO layers. The electrical characterization of the layers includes measurements of the recombination current densities J0 via photoconductance decay and the contact resistances between aluminum and the printed Si layer and between poly-Si and substrate via transfer length method. We print the ink on one side of the wafer in quadratic fields with an area of 4 x 4 cm2, which is a suitable size for the measurements. The rear side of the wafer is passivated with a silicon nitride passivation layer. We investigate the influence of two process parameters on the electrical properties of the POLO contacts: the thickness of the printed liquid Si layer and the thermal budget of the annealing process. For several poly-Si layer thicknesses and annealing temperatures between 900°C and 1000°C, we achieve J0 of the first P-doped inkjet-printed POLO contacts of < 20 fA/cm2 with a minimum value of 14 fA/cm2. }, note = {2018 MRS Fall Meeting & Exhibit}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } The increase of Si solar cell efficiencies in the last years have been mainly driven by passivating contacts, either with amorphous Si (heterostructure with intrinsic thin layer, HIT) or silicon oxide (poly-Si on oxide, POLO; tunnel oxide passivating contact, TopCon) as an interface layer [1-3]. Interdigitated back-contact (IBC) solar cells have demonstrated the highest efficiencies of more than 26 % [4,5], as they combine a high voltage resulting from the passivating contacts and a higher current compared to front-contacted solar cells due to the absence of metal shading. A drawback shared by all presented techniques for the deposition of POLO contacts so far is that they cover the full area of one or both sides of the wafer [6]. During the process of an IBC Si solar cell, a structuring of the deposited poly-Si layer is necessary. To overcome these hurdles, Evonik developed an inkjet printable, doped precursor (Evonik’s liquid silicon) which can be used for the direct generation of structured amorphous and polycrystalline Si layers [7,8]. As direct printing on silicon oxide layers used for POLO junctions is possible, this is a novel, unique possibility to prepare in-situ doped and in-situ structured poly-Si layers with only three process steps: Printing of the liquid Si ink onto the wafer under inert atmosphere with an inkjet printer – conversion of the liquid Si into amorphous Si on a hotplate – annealing of the layer stack in a tube furnace with break-up of the silicon oxide and conversion of the amorphous Si into poly-Si. The shape of the printed Si layer can be designed freely, the minimum structure size of the printed POLO contact is limited only by the drop size of the inkjet process. In this work, we present the preparation and properties of phosphorous-doped inkjet-printed POLO layers. The electrical characterization of the layers includes measurements of the recombination current densities J0 via photoconductance decay and the contact resistances between aluminum and the printed Si layer and between poly-Si and substrate via transfer length method. We print the ink on one side of the wafer in quadratic fields with an area of 4 x 4 cm2, which is a suitable size for the measurements. The rear side of the wafer is passivated with a silicon nitride passivation layer. We investigate the influence of two process parameters on the electrical properties of the POLO contacts: the thickness of the printed liquid Si layer and the thermal budget of the annealing process. For several poly-Si layer thicknesses and annealing temperatures between 900°C and 1000°C, we achieve J0 of the first P-doped inkjet-printed POLO contacts of < 20 fA/cm2 with a minimum value of 14 fA/cm2.
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R. Peibst, N. Folchert, F. Haase, C. Klamt, Y. Larionova, J. Krügener, A. Merkle, B. Min, M. Rienaecker, U. Römer, S. Schäfer, D. Tetzlaff, T. Wietler, and R. Brendel In-Depth Study of poly-Si / Oxide / c -Si Junctions and p+ poly-Si / n+ poly-Si Tunneling Junctions f or Applications in Si Single Junction and Si- Based Tandem Cells Vortrag Boston, MA, USA, 26.11.2018, (2018 MRS Fall Meeting & Exhibit). Abstract | BibTeX | Schlagwörter: POLO @misc{Peibst2018d,
title = {In-Depth Study of poly-Si / Oxide / c -Si Junctions and p+ poly-Si / n+ poly-Si Tunneling Junctions f or Applications in Si Single Junction and Si- Based Tandem Cells}, author = {R Peibst and N Folchert and F Haase and C Klamt and Y Larionova and J Krügener and A Merkle and B Min and M Rienaecker and U Römer and S Schäfer and D Tetzlaff and T Wietler and R Brendel}, year = {2018}, date = {2018-11-26}, address = {Boston, MA, USA}, abstract = {Passivating contacts based on a stack of polycrystalline (poly-) Si on a thin interfacial oxide (POLO) are attracting enormous research interest in crystalline (c-) Si photovoltaics. Its excellent passivation quality with emitter saturation current densities below 1 fA/cm2, in combination with junction resistances in the sub-mΩcm2 regime, result in a high carrier extraction selectivity S10 with an efficiency potential of an otherwise ideal Si single junction cell beyond 28 %. Three contributions of our group to this interesting research field will be reported: First, theoretical investigations of the current transport mechanism through these POLO junctions suggest a dominant contribution of pinhole-mediated current. These pinholes are experimentally verified post-priori with an excellent agreement between predicted and measured pinhole areal density. The temperature dependency of the junction resistance can be well described with our pinhole model. Second, we demonstrate the efficiency potential of the POLO-junctions on cell level. We so far achieved a record efficiency value for p-type Si material of 26.1%. On this back-junction back-contacted cell, the p+ type doped and n+ type doped poly-Si fingers are separated by a region of intrinsic poly-Si. Third, we combine an electron colleting n+ POLO junction on a p-type Si cell with a p+ type poly-Si layer to form a low-resistive tunneling junction as an interface of bottom and top cell for Si based tandem applications. The carrier lifetimes in the poly-Si of 42-54 ps, as experimentally determined by time-resolved photoluminescence, are used as input parameters for numerical Sentaurus simulations of our p+ poly-Si / n+ poly-Si tunneling junctions. These simulations reveal the importance of nonlocal band-to-band and especially trap-assisted tunneling for a low junction resistivity. Experimentally, a contact resistance of 7.4 mΩcm2 for the entire (Al) / p+ poly-Si / n+ poly-Si / SiOx / c-Si stack is determined, which is sufficiently low for a full area contact between bottom and top cell. }, note = {2018 MRS Fall Meeting & Exhibit}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } Passivating contacts based on a stack of polycrystalline (poly-) Si on a thin interfacial oxide (POLO) are attracting enormous research interest in crystalline (c-) Si photovoltaics. Its excellent passivation quality with emitter saturation current densities below 1 fA/cm2, in combination with junction resistances in the sub-mΩcm2 regime, result in a high carrier extraction selectivity S10 with an efficiency potential of an otherwise ideal Si single junction cell beyond 28 %. Three contributions of our group to this interesting research field will be reported: First, theoretical investigations of the current transport mechanism through these POLO junctions suggest a dominant contribution of pinhole-mediated current. These pinholes are experimentally verified post-priori with an excellent agreement between predicted and measured pinhole areal density. The temperature dependency of the junction resistance can be well described with our pinhole model. Second, we demonstrate the efficiency potential of the POLO-junctions on cell level. We so far achieved a record efficiency value for p-type Si material of 26.1%. On this back-junction back-contacted cell, the p+ type doped and n+ type doped poly-Si fingers are separated by a region of intrinsic poly-Si. Third, we combine an electron colleting n+ POLO junction on a p-type Si cell with a p+ type poly-Si layer to form a low-resistive tunneling junction as an interface of bottom and top cell for Si based tandem applications. The carrier lifetimes in the poly-Si of 42-54 ps, as experimentally determined by time-resolved photoluminescence, are used as input parameters for numerical Sentaurus simulations of our p+ poly-Si / n+ poly-Si tunneling junctions. These simulations reveal the importance of nonlocal band-to-band and especially trap-assisted tunneling for a low junction resistivity. Experimentally, a contact resistance of 7.4 mΩcm2 for the entire (Al) / p+ poly-Si / n+ poly-Si / SiOx / c-Si stack is determined, which is sufficiently low for a full area contact between bottom and top cell.
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B. A. Veith-Wolf, S. Schäfer, R. Brendel, and J. Schmidt Solar Energy Materials and Solar Cells 186 , 194-199, (2018), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: Aluminum oxide, Auger recombination, charge carrier lifetime, Intrinsic lifetime, silicon, surface passivation @article{Veith-Wolf2018b,
title = {Reassessment of intrinsic lifetime limit in n-type crystalline silicon and implication on maximum solar cell efficiency}, author = {B A Veith-Wolf and S Schäfer and R Brendel and J Schmidt}, doi = {10.1016/j.solmat.2018.06.029}, issn = {0927-0248}, year = {2018}, date = {2018-11-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {186}, pages = {194-199}, abstract = {Unusually high carrier lifetimes are measured by photoconductance decay on n-type Czochralski-grown silicon wafers of different doping concentrations, passivated using plasma-assisted atomic-layer-deposited aluminum oxide (Al2O3) on both wafer surfaces. The measured effective lifetimes significantly exceed the intrinsic lifetime limit previously reported in the literature. Several prerequisites have to be fulfilled to allow the measurement of such high lifetimes on Al2O3-passivated n-type silicon wafers: (i) large-area wafers are required to minimize the impact of edge recombination via the Al2O3-charge-induced inversion layer, (ii) an exceptionally homogeneous Al2O3 surface passivation is required, and (iii) very thick silicon wafers are needed. Based on our lifetime measurements on n-type silicon wafers of different doping concentrations, we introduce a new parameterization of the intrinsic lifetime for n-type crystalline silicon. This new parameterization has implications concerning the maximum reachable efficiency of n-type silicon solar cells, which is larger than assumed before.}, keywords = {Aluminum oxide, Auger recombination, charge carrier lifetime, Intrinsic lifetime, silicon, surface passivation}, pubstate = {published}, tppubtype = {article} } Unusually high carrier lifetimes are measured by photoconductance decay on n-type Czochralski-grown silicon wafers of different doping concentrations, passivated using plasma-assisted atomic-layer-deposited aluminum oxide (Al2O3) on both wafer surfaces. The measured effective lifetimes significantly exceed the intrinsic lifetime limit previously reported in the literature. Several prerequisites have to be fulfilled to allow the measurement of such high lifetimes on Al2O3-passivated n-type silicon wafers: (i) large-area wafers are required to minimize the impact of edge recombination via the Al2O3-charge-induced inversion layer, (ii) an exceptionally homogeneous Al2O3 surface passivation is required, and (iii) very thick silicon wafers are needed. Based on our lifetime measurements on n-type silicon wafers of different doping concentrations, we introduce a new parameterization of the intrinsic lifetime for n-type crystalline silicon. This new parameterization has implications concerning the maximum reachable efficiency of n-type silicon solar cells, which is larger than assumed before.
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F. Haase, C. Hollemann, S. Schäfer, A. Merkle, M. Rienäcker, J. Krügener, R. Brendel, and R. Peibst Solar Energy Materials and Solar Cells 186 , 184-193, (2018), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: Back-contact solar cell, Laser, passivating contacts, POLO @article{Haase2018c,
title = {Laser contact openings for local poly-Si-metal contacts enabling 26.1%-efficient POLO-IBC solar cells}, author = {F Haase and C Hollemann and S Schäfer and A Merkle and M Rienäcker and J Krügener and R Brendel and R Peibst}, doi = {10.1016/j.solmat.2018.06.020}, issn = {0927-0248}, year = {2018}, date = {2018-11-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {186}, pages = {184-193}, abstract = {We demonstrate damage-free laser contact openings in silicon oxide layers on polycrystalline silicon on oxide (POLO) passivating contacts. A pulsed UV-laser evaporates the upper part of the polycrystalline silicon layer, lifting off the silicon oxide layer on top. On n-type POLO (and p-type POLO, respectively) samples a saturation current density of 2 fA cm−2 (6 fA cm−2) and an implied open-circuit voltage of 733 mV (727 mV) are achieved with a laser contact opening area fraction of 12.3% (8.7%). The application of this ablation process in an interdigitated back contact solar cell leads to an independently confirmed power conversion efficiency of 26.1%. The excellent contact quality of the laser contact openings is proven by the low series resistance of 0.1 Ω cm2 on the solar cell with a contact area of only 3%.}, keywords = {Back-contact solar cell, Laser, passivating contacts, POLO}, pubstate = {published}, tppubtype = {article} } We demonstrate damage-free laser contact openings in silicon oxide layers on polycrystalline silicon on oxide (POLO) passivating contacts. A pulsed UV-laser evaporates the upper part of the polycrystalline silicon layer, lifting off the silicon oxide layer on top. On n-type POLO (and p-type POLO, respectively) samples a saturation current density of 2 fA cm−2 (6 fA cm−2) and an implied open-circuit voltage of 733 mV (727 mV) are achieved with a laser contact opening area fraction of 12.3% (8.7%). The application of this ablation process in an interdigitated back contact solar cell leads to an independently confirmed power conversion efficiency of 26.1%. The excellent contact quality of the laser contact openings is proven by the low series resistance of 0.1 Ω cm2 on the solar cell with a contact area of only 3%.
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M. Köntges, H. Schulte-Huxel, S. Blankemeyer, M. R. Vogt, H. Holst, and R. Reineke-Koch Measuring the light recovery factor of backsheets in photovoltaic modules Artikel Solar Energy Materials and Solar Cells 186 , 175-183, (2018), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: Backsheet, light harvesting, Light Trapping, Module efficiency, PV Module @article{Köntges2018b,
title = {Measuring the light recovery factor of backsheets in photovoltaic modules}, author = {M Köntges and H Schulte-Huxel and S Blankemeyer and M R Vogt and H Holst and R Reineke-Koch}, doi = {10.1016/j.solmat.2018.06.028}, issn = {0927-0248}, year = {2018}, date = {2018-11-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {186}, pages = {175-183}, abstract = {We measure the short circuit current improvement of various commercial backsheets for passivated emitter and rear solar cells (PERC) in photovoltaic (PV) modules. We quantify this improvement by a light recovery factor k defined as the share of the light reflected by the backsheet around the cell in a PV module laminate, which is converted into electrical current by the solar cells in the module relative to a reference rear surface. The presented measurement method allows measuring the light recovery factor as function of the incident light beam angle, which are important for the calculation of the yield analysis in the field. Simulations of the recovery factor with the optical ray tracing program DIADALOS are performed in order to support the interpretation of the results. For measuring the absolute light recovery probability of a backsheet one should use a reference backsheet with an absorbance of close to 100% to avoid systematic reflection errors especially for high incident light beam angles > 50°. The ranking of various recovery factors are compared to the ranking measured by reflectance measurements defined in standard IEC 62788-2 Ed.1 for backsheets. The standard shows a substantial deviation between the ranking of recovery factor and the reflectance which can be corrected by using an adapted definition for the reflectance measurement method.}, keywords = {Backsheet, light harvesting, Light Trapping, Module efficiency, PV Module}, pubstate = {published}, tppubtype = {article} } We measure the short circuit current improvement of various commercial backsheets for passivated emitter and rear solar cells (PERC) in photovoltaic (PV) modules. We quantify this improvement by a light recovery factor k defined as the share of the light reflected by the backsheet around the cell in a PV module laminate, which is converted into electrical current by the solar cells in the module relative to a reference rear surface. The presented measurement method allows measuring the light recovery factor as function of the incident light beam angle, which are important for the calculation of the yield analysis in the field. Simulations of the recovery factor with the optical ray tracing program DIADALOS are performed in order to support the interpretation of the results. For measuring the absolute light recovery probability of a backsheet one should use a reference backsheet with an absorbance of close to 100% to avoid systematic reflection errors especially for high incident light beam angles > 50°. The ranking of various recovery factors are compared to the ranking measured by reflectance measurements defined in standard IEC 62788-2 Ed.1 for backsheets. The standard shows a substantial deviation between the ranking of recovery factor and the reflectance which can be corrected by using an adapted definition for the reflectance measurement method.
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M. Schnabel, M. Rienäcker, E. L. Warren, J. F. Geisz, R. Peibst, P. Stradins, and A. C. Tamboli Equivalent Performance in Three-Terminal and Four-Terminal Tandem Solar Cells Artikel IEEE Journal of Photovoltaics 8 (6), 1584-1589, (2018), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Absorption, Computer architecture, Current measurement, Density measurement, III-V semiconductor materials, Microprocessors, Photovoltaic cells, Power system measurements, silicon @article{Schnabel2018b,
title = {Equivalent Performance in Three-Terminal and Four-Terminal Tandem Solar Cells}, author = {M Schnabel and M Rienäcker and E L Warren and J F Geisz and R Peibst and P Stradins and A C Tamboli}, doi = {10.1109/JPHOTOV.2018.2865175}, issn = {2156-3381}, year = {2018}, date = {2018-11-01}, journal = {IEEE Journal of Photovoltaics}, volume = {8}, number = {6}, pages = {1584-1589}, abstract = {Tandem or multijunction solar cells are a promising method to circumvent the efficiency limit of single-junction solar cells, but there is ongoing debate over how best to interconnect the subcells in a tandem cell. In addition to four-terminal and two-terminal tandem cell architectures, a new three-terminal tandem cell architecture has recently been demonstrated, which features a standard two-terminal (front-back) circuit as well as an interdigitated back contact (IBC) circuit connected to the bottom cell. It has no middle contacts, and thus, maintains some of the simplicity of a two-terminal tandem. In this study, we measure four-terminal GaInP//Si and GaInP/GaAs//Si tandem cells in four-terminal and three-terminal configurations by connecting wires to mimic a three-terminal architecture. We demonstrate that both modes allow the same efficiencies exceeding 30% to be attained. Furthermore, we show that the IBC circuit not only collects excess power from the bottom cell, but that it can inject power into the bottom cell if it is current limiting the front-back circuit, enabling four-terminal performance in monolithic structures, regardless of which cell delivers less current.}, keywords = {Absorption, Computer architecture, Current measurement, Density measurement, III-V semiconductor materials, Microprocessors, Photovoltaic cells, Power system measurements, silicon}, pubstate = {published}, tppubtype = {article} } Tandem or multijunction solar cells are a promising method to circumvent the efficiency limit of single-junction solar cells, but there is ongoing debate over how best to interconnect the subcells in a tandem cell. In addition to four-terminal and two-terminal tandem cell architectures, a new three-terminal tandem cell architecture has recently been demonstrated, which features a standard two-terminal (front-back) circuit as well as an interdigitated back contact (IBC) circuit connected to the bottom cell. It has no middle contacts, and thus, maintains some of the simplicity of a two-terminal tandem. In this study, we measure four-terminal GaInP//Si and GaInP/GaAs//Si tandem cells in four-terminal and three-terminal configurations by connecting wires to mimic a three-terminal architecture. We demonstrate that both modes allow the same efficiencies exceeding 30% to be attained. Furthermore, we show that the IBC circuit not only collects excess power from the bottom cell, but that it can inject power into the bottom cell if it is current limiting the front-back circuit, enabling four-terminal performance in monolithic structures, regardless of which cell delivers less current.
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F. Haase, J. Käsewieter, S. R. Nabavi, E. Jansen, R. Rolfes, and M. Köntges IEEE Journal of Photovoltaics 8 (6), 1510-1524, (2018), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Crack, mechanical loading, photovoltaic (PV) module, Silicon solar cell @article{Haase2018c,
title = {Fracture Probability, Crack Patterns, and Crack Widths of Multicrystalline Silicon Solar Cells in PV Modules During Mechanical Loading}, author = {F Haase and J Käsewieter and S R Nabavi and E Jansen and R Rolfes and M Köntges}, doi = {10.1109/JPHOTOV.2018.2871338}, issn = {2156-3381}, year = {2018}, date = {2018-11-01}, journal = {IEEE Journal of Photovoltaics}, volume = {8}, number = {6}, pages = {1510-1524}, abstract = {We experimentally analyze the position and opening behavior of cracks in multicrystalline silicon solar cells laminated in standard-sized frameless modules during mechanical loading in a 4-line-bending setup. The results of the experiment are reproduced by simulations for a standard module. These simulations open the opportunity to simulate also complex load situations. Cell interconnect ribbons have big influence to which critically extended module can be bended until a crack appears. Modules with cell interconnect ribbons that are parallel to the bending axis can be bended four times less until cell cracking than modules with cell interconnect ribbons oriented perpendicular to the bending axis and two times less compared with a module without cell interconnect ribbons. Small edge cracks parallel to the bending axis and cross cracks at the busbar decrease the critical bending in the module by a factor of four compared to small edge cracks perpendicular to the bending axis and crack-free cells. The presence of the backsheet decreases the crack width during mechanical loading by 30% compared to a module without a backsheet. In the standard module, the crack width of a single crack is 3.4 μm at loads comparable to the IEC 61215 5400 Pa test.}, keywords = {Crack, mechanical loading, photovoltaic (PV) module, Silicon solar cell}, pubstate = {published}, tppubtype = {article} } We experimentally analyze the position and opening behavior of cracks in multicrystalline silicon solar cells laminated in standard-sized frameless modules during mechanical loading in a 4-line-bending setup. The results of the experiment are reproduced by simulations for a standard module. These simulations open the opportunity to simulate also complex load situations. Cell interconnect ribbons have big influence to which critically extended module can be bended until a crack appears. Modules with cell interconnect ribbons that are parallel to the bending axis can be bended four times less until cell cracking than modules with cell interconnect ribbons oriented perpendicular to the bending axis and two times less compared with a module without cell interconnect ribbons. Small edge cracks parallel to the bending axis and cross cracks at the busbar decrease the critical bending in the module by a factor of four compared to small edge cracks perpendicular to the bending axis and crack-free cells. The presence of the backsheet decreases the crack width during mechanical loading by 30% compared to a module without a backsheet. In the standard module, the crack width of a single crack is 3.4 μm at loads comparable to the IEC 61215 5400 Pa test.
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I. Romijn, G. Janssen, T. Dullweber, B. van Aken, N. Eisenberg, L. Kreinin, M. Despeisse, V. Mihailetchi, J. Lossen, W. Jooss, and R. Kopecek Bifacial cells Buchkapitel R. Kopecek, and J. Libal (Hrsg.): Bifacial Photovoltaics: Technology, applications and economics, Kapitel 2, Institution of Engineering and Technology, (2018), ISBN: 978-1-78561-274-9. Links | BibTeX | Schlagwörter: Bifacial, Characterization, common cell architectures, history, n-type bifacial solar cells, p-type bifacial solar cells, partial metallization, PV modules, review, solar cell physics @inbook{Romijn2018,
title = {Bifacial cells}, author = {I Romijn and G Janssen and T Dullweber and B van Aken and N Eisenberg and L Kreinin and M Despeisse and V Mihailetchi and J Lossen and W Jooss and R Kopecek}, editor = {R Kopecek and J Libal}, doi = {10.1049/PBPO107E_ch2}, isbn = {978-1-78561-274-9}, year = {2018}, date = {2018-11-01}, booktitle = {Bifacial Photovoltaics: Technology, applications and economics}, publisher = {Institution of Engineering and Technology}, chapter = {2}, keywords = {Bifacial, Characterization, common cell architectures, history, n-type bifacial solar cells, p-type bifacial solar cells, partial metallization, PV modules, review, solar cell physics}, pubstate = {published}, tppubtype = {inbook} } |
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I. Kröger, D. Friedrich, S. Winter, E. Salis, H. Müllejans, D. Pavanello, J. Hohl-Ebinger, K. Bothe, D. Hinken, S. Dittmann, G. Friesen, M. Bliss, T. Betts, R. Gottschalg, L. Rimmelspacher, J. Stang, W. Herrmann, and J. Dubard Results of the round robin calibration of reference solar cells within the PhotoClass project Artikel Int. J. Metrol. Qual. Eng. 9 , 8, (2018). Abstract | Links | BibTeX | Schlagwörter: calibration, reference solar cell, Round Robin, standard test conditions @article{Kröger2018,
title = {Results of the round robin calibration of reference solar cells within the PhotoClass project}, author = {I Kröger and D Friedrich and S Winter and E Salis and H Müllejans and D Pavanello and J Hohl-Ebinger and K Bothe and D Hinken and S Dittmann and G Friesen and M Bliss and T Betts and R Gottschalg and L Rimmelspacher and J Stang and W Herrmann and J Dubard}, doi = {10.1051/ijmqe/2018006}, year = {2018}, date = {2018-10-17}, journal = {Int. J. Metrol. Qual. Eng.}, volume = {9}, pages = {8}, abstract = {An intercomparison of terrestrial photovoltaic (PV) calibrations was performed among a number of European calibration and testing laboratories that participated in the European Metrology Research Program (EMRP) project “PhotoClass”. The purpose of this intercomparison was to evaluate the comparability of calibration and testing services within the stated uncertainties of the individual laboratories. The calibration objects were two world photovoltaic scale (WPVS)-type reference solar cells, one made from crystalline silicon and one made from GaAs. The calibration value (CV) was the short-circuit current under standard test conditions (ISTC). In conclusion, it was found that the CVs are all consistent within the stated uncertainties. This result strengthens the reliance in the calibration chain and in the PV calibration infrastructure in Europe.}, keywords = {calibration, reference solar cell, Round Robin, standard test conditions}, pubstate = {published}, tppubtype = {article} } An intercomparison of terrestrial photovoltaic (PV) calibrations was performed among a number of European calibration and testing laboratories that participated in the European Metrology Research Program (EMRP) project “PhotoClass”. The purpose of this intercomparison was to evaluate the comparability of calibration and testing services within the stated uncertainties of the individual laboratories. The calibration objects were two world photovoltaic scale (WPVS)-type reference solar cells, one made from crystalline silicon and one made from GaAs. The calibration value (CV) was the short-circuit current under standard test conditions (ISTC). In conclusion, it was found that the CVs are all consistent within the stated uncertainties. This result strengthens the reliance in the calibration chain and in the PV calibration infrastructure in Europe.
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A. Morlier, M. Siebert, and M. Köntges Basics of UV fluorescence Vortrag Emmerthal, Germany, 12.10.2018, (Workshop on UV Fluorescence Measurement for Damage Assessment of PV Modules). Links | BibTeX | Schlagwörter: UV fluorescence @misc{Morlier2018c,
title = {Basics of UV fluorescence}, author = {A Morlier and M Siebert and M Köntges}, url = {https://isfh.de/publikationen/isfh-workshops-proceedings/uv-fluorescence-workshop/}, year = {2018}, date = {2018-10-12}, booktitle = {Workshop on UV Fluorescence Measurement for Damage Assessment of PV Modules}, address = {Emmerthal, Germany}, note = {Workshop on UV Fluorescence Measurement for Damage Assessment of PV Modules}, keywords = {UV fluorescence}, pubstate = {published}, tppubtype = {presentation} } |
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M. Siebert, A. Morlier, and M. Köntges Temperature effect on UV fluorescence Vortrag Emmerthal, Germany, 12.10.2018, (Workshop on UV Fluorescence Measurement for Damage Assessment of PV Modules). Links | BibTeX | Schlagwörter: UV fluorescence @misc{Siebert2018,
title = {Temperature effect on UV fluorescence}, author = {M Siebert and A Morlier and M Köntges}, url = {https://isfh.de/publikationen/isfh-workshops-proceedings/uv-fluorescence-workshop/}, year = {2018}, date = {2018-10-12}, address = {Emmerthal, Germany}, note = {Workshop on UV Fluorescence Measurement for Damage Assessment of PV Modules}, keywords = {UV fluorescence}, pubstate = {published}, tppubtype = {presentation} } |
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N. Folchert, M. Rienäcker, A. A. Yeo, B. Min, R. Peibst, and R. Brendel Temperature-dependent contact resistance of carrier selective Poly-Si on oxide junctions Artikel Solar Energy Materials and Solar Cells 185 , 425-430, (2018), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: Contact resistance, passivating contacts, Pinhole transport, POLO, Poly-Si, selective contacts, Transfer-length-method, Tunneling @article{Folchert2018b,
title = {Temperature-dependent contact resistance of carrier selective Poly-Si on oxide junctions}, author = {N Folchert and M Rienäcker and A A Yeo and B Min and R Peibst and R Brendel}, doi = {10.1016/j.solmat.2018.05.046}, issn = {0927-0248}, year = {2018}, date = {2018-10-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {185}, pages = {425-430}, abstract = {Abstract Carrier selective junctions using a poly-silicon/ silicon oxide stack on crystalline silicon feature low recombination currents \{J0\} whilst allowing for low contact resistivity ρ C . We describe the limiting current transport mechanism as a combination of homogeneous tunneling through the interfacial silicon oxide layer and transport through pinholes where the interfacial silicon oxide layer is locally disrupted. We present an experimental method and its theoretical basis to discriminate between homogenous tunneling and local pinhole transport mechanisms on n + /n or p + /p junctions by measuring the temperature-dependent contact resistance. Theory predicts opposing trends for the temperature dependencies of tunneling and pinhole transport. This allows identifying the dominant transport path. For the contact resistance of two differently prepared poly-Si/ silicon oxide/ c-Si junctions we either find clear pinhole-type or clear tunneling-type temperature dependence. Pinhole transport contributes more than 94 % to the total current for the sample with a 2.1 nm-thick interfacial silicon oxide that we anneal at a temperature of 1050 °C to achieve highest selectivity. In contrast pinhole transport contributes less than 35 % to the total current for the sample with a 1.7 nm-thick silicon oxide that we annealed at only 700 °C in order to avoid pinholes.}, keywords = {Contact resistance, passivating contacts, Pinhole transport, POLO, Poly-Si, selective contacts, Transfer-length-method, Tunneling}, pubstate = {published}, tppubtype = {article} } Abstract Carrier selective junctions using a poly-silicon/ silicon oxide stack on crystalline silicon feature low recombination currents {J0} whilst allowing for low contact resistivity ρ C . We describe the limiting current transport mechanism as a combination of homogeneous tunneling through the interfacial silicon oxide layer and transport through pinholes where the interfacial silicon oxide layer is locally disrupted. We present an experimental method and its theoretical basis to discriminate between homogenous tunneling and local pinhole transport mechanisms on n + /n or p + /p junctions by measuring the temperature-dependent contact resistance. Theory predicts opposing trends for the temperature dependencies of tunneling and pinhole transport. This allows identifying the dominant transport path. For the contact resistance of two differently prepared poly-Si/ silicon oxide/ c-Si junctions we either find clear pinhole-type or clear tunneling-type temperature dependence. Pinhole transport contributes more than 94 % to the total current for the sample with a 2.1 nm-thick interfacial silicon oxide that we anneal at a temperature of 1050 °C to achieve highest selectivity. In contrast pinhole transport contributes less than 35 % to the total current for the sample with a 1.7 nm-thick silicon oxide that we annealed at only 700 °C in order to avoid pinholes.
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L. Helmich, D. C. Walter, D. Bredemeier, R. Falster, V. V. Voronkov, and J. Schmidt In-situ characterization of electron-assisted regeneration of Cz-Si solar cells Artikel Solar Energy Materials and Solar Cells 185 , 283-286, (2018), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: boron-oxygen defect, Czochralski-grown silicon, LID, regeneration, solar cell @article{Helmich2018b,
title = {In-situ characterization of electron-assisted regeneration of Cz-Si solar cells}, author = {L Helmich and D C Walter and D Bredemeier and R Falster and V V Voronkov and J Schmidt}, doi = {10.1016/j.solmat.2018.05.023}, issn = {0927-0248}, year = {2018}, date = {2018-10-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {185}, pages = {283-286}, abstract = {Abstract We examine the regeneration kinetics of passivated emitter and rear solar cells (PERCs) fabricated on boron-doped p-type Czochralski-grown silicon wafers in darkness by electron injection via application of a forward bias voltage at elevated temperature (140 °C) in order to discriminate between electronic and photonic effects. Based on these dark regeneration experiments, we address the existing inconsistency regarding the measured linear dependence of the regeneration rate constant on the excess carrier density. Using the method of dark regeneration by current injection into the solar cell, we are able to measure the total recombination current of the solar cell at the actual regeneration temperature under applied voltage, i.e., at the physically relevant regeneration conditions. The direct comparison of the regeneration rate constant as a function of electronically injected carrier concentration in the dark and the regeneration rate constant during illumination clearly shows that the regeneration is a purely electronically stimulated effect and that photons are not directly involved.}, keywords = {boron-oxygen defect, Czochralski-grown silicon, LID, regeneration, solar cell}, pubstate = {published}, tppubtype = {article} } Abstract We examine the regeneration kinetics of passivated emitter and rear solar cells (PERCs) fabricated on boron-doped p-type Czochralski-grown silicon wafers in darkness by electron injection via application of a forward bias voltage at elevated temperature (140 °C) in order to discriminate between electronic and photonic effects. Based on these dark regeneration experiments, we address the existing inconsistency regarding the measured linear dependence of the regeneration rate constant on the excess carrier density. Using the method of dark regeneration by current injection into the solar cell, we are able to measure the total recombination current of the solar cell at the actual regeneration temperature under applied voltage, i.e., at the physically relevant regeneration conditions. The direct comparison of the regeneration rate constant as a function of electronically injected carrier concentration in the dark and the regeneration rate constant during illumination clearly shows that the regeneration is a purely electronically stimulated effect and that photons are not directly involved.
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C. Klamt, M. Rienäcker, F. Haase, N. Folchert, R. Brendel, R. Peibst, V. Krausse, and J. Krügener Intrinsic Poly-Crystalline Silicon Region in between the p+ and n+ POLO Contacts of an 26.1%-Efficient IBC Solar Cell Vortrag Brussels, Belgium, 26.09.2018, (35th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Schlagwörter: POLO @misc{Klamt2018,
title = { Intrinsic Poly-Crystalline Silicon Region in between the p+ and n+ POLO Contacts of an 26.1%-Efficient IBC Solar Cell}, author = {C Klamt and M Rienäcker and F Haase and N Folchert and R Brendel and R Peibst and V Krausse and J Krügener}, editor = {WIP}, year = {2018}, date = {2018-09-26}, booktitle = {Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition}, address = {Brussels, Belgium}, abstract = {We investigate the impact of an intrinsic poly-crystalline silicon (i poly-Si) region between p+-type poly-Si and n+- type poly-Si regions in interdigitated back contacted solar cells with poly Si on oxide (POLO) passivating contacts. The purpose of these i poly-Si regions is to avoid a lateral pn poly-Si junction between the BSF and emitter fingers, which would mediate a high recombination current. Regarding this aspect, large i poly-Si region widths are preferable. On the other hand, we observe on full-area lifetime test structures a poor passivation of the crystalline Si absorber by the intrinsic poly-Si, corresponding to saturation current density of 309 fA/cm2. Regarding this aspect, small i poly-Si region widths are preferable. In order to find an optimum between these counteracting requirements, we perform a systematic investigation on poly-Si pin diode test structures with varying i poly-Si region widths from dgap = 0 to 380 μm. We indeed observe a strong decrease of the pin diode recombination current density J with increasing i region width, especially in the range between 30 and 40 μm where J changes over four orders of magnitude. Already for an i region width of 20 μm, the recombination current density of the pin diode is one order of magnitude smaller than the total recombination current density of our cells and is therefore not limiting the device performance any more. We consequently apply an i poly-Si width of 30 μm to a POLO interdigitated back contacted (IBC) solar cell and achieve an independently confirmed energy conversion efficiency of 26.1% [2]. Puzzlingly, the area-weighted J0 value of the 30 μm small i region (41.2 fA/cm2) is not consistent with the total J01 value measured on our cell (21 fA/cm2). Obviously, the passivation of the crystalline absorber by the intrinsic poly-Si areas embedded in the pin diodes is much better than on full-area lifetime test structures. Our hypothesis explaining this observation is that during the high-temperature POLOjunction formation step a lateral diffusion of the p+-type and n+-type dopants into the initially intrinsic region takes place. We confirm experimentally that this significantly reduces the actual width of the intrinsic poly-Si region.}, note = {35th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } We investigate the impact of an intrinsic poly-crystalline silicon (i poly-Si) region between p+-type poly-Si and n+- type poly-Si regions in interdigitated back contacted solar cells with poly Si on oxide (POLO) passivating contacts. The purpose of these i poly-Si regions is to avoid a lateral pn poly-Si junction between the BSF and emitter fingers, which would mediate a high recombination current. Regarding this aspect, large i poly-Si region widths are preferable. On the other hand, we observe on full-area lifetime test structures a poor passivation of the crystalline Si absorber by the intrinsic poly-Si, corresponding to saturation current density of 309 fA/cm2. Regarding this aspect, small i poly-Si region widths are preferable. In order to find an optimum between these counteracting requirements, we perform a systematic investigation on poly-Si pin diode test structures with varying i poly-Si region widths from dgap = 0 to 380 μm. We indeed observe a strong decrease of the pin diode recombination current density J with increasing i region width, especially in the range between 30 and 40 μm where J changes over four orders of magnitude. Already for an i region width of 20 μm, the recombination current density of the pin diode is one order of magnitude smaller than the total recombination current density of our cells and is therefore not limiting the device performance any more. We consequently apply an i poly-Si width of 30 μm to a POLO interdigitated back contacted (IBC) solar cell and achieve an independently confirmed energy conversion efficiency of 26.1% [2]. Puzzlingly, the area-weighted J0 value of the 30 μm small i region (41.2 fA/cm2) is not consistent with the total J01 value measured on our cell (21 fA/cm2). Obviously, the passivation of the crystalline absorber by the intrinsic poly-Si areas embedded in the pin diodes is much better than on full-area lifetime test structures. Our hypothesis explaining this observation is that during the high-temperature POLOjunction formation step a lateral diffusion of the p+-type and n+-type dopants into the initially intrinsic region takes place. We confirm experimentally that this significantly reduces the actual width of the intrinsic poly-Si region.
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V. Titova, and J. Schmidt Implementation of full-area-deposited electron-selective TiOx layers into silicon solar cells Vortrag Brussels, Belgium, 26.09.2018, (35th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Schlagwörter: TiOx @misc{Titova2018b,
title = {Implementation of full-area-deposited electron-selective TiOx layers into silicon solar cells}, author = {V Titova and J Schmidt}, year = {2018}, date = {2018-09-26}, address = {Brussels, Belgium}, abstract = {We present results of crystalline silicon solar cells with an electron-selective contact provided by ultrathin titanium oxide (TiOx) films deposited by atomic layer deposition (ALD). We combine a SiOy/TiOx/Al electron-selective rear contact and a boron-diffused emitter passivated by an Al2O3/SiNx stack at the cell front on an n-type Cz-Si wafer. An open-circuit voltage of 661 mV is achieved for a solar cell with a 3 nm thick TiOx layer. For thinner TiOx layers the passivation quality is reduced, however, the solar cells still show open-circuit voltage exceeding 650 mV. An effective surface passivation of the cell rear is an important prerequisite for obtaining high efficiencies. In a first cell run, we demonstrate the feasibility of this concept, however, the actual cell efficiency of 20.3% is not limited by the TiOx layer selectivity, but by a reduced short-circuit current density Jsc and an increased series resistance Rs. By varying the metallization grid design on the front side, a series resistance of only 0.3 Ωcm2 was achieved, which directly correlates with a significant improvement in fill factor to 81.2%, clearly demonstrating that the ultrathin TiOx layer allows a good transport of majority carriers (electrons) and an effective blocking of minority carriers.}, note = {35th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {TiOx}, pubstate = {published}, tppubtype = {presentation} } We present results of crystalline silicon solar cells with an electron-selective contact provided by ultrathin titanium oxide (TiOx) films deposited by atomic layer deposition (ALD). We combine a SiOy/TiOx/Al electron-selective rear contact and a boron-diffused emitter passivated by an Al2O3/SiNx stack at the cell front on an n-type Cz-Si wafer. An open-circuit voltage of 661 mV is achieved for a solar cell with a 3 nm thick TiOx layer. For thinner TiOx layers the passivation quality is reduced, however, the solar cells still show open-circuit voltage exceeding 650 mV. An effective surface passivation of the cell rear is an important prerequisite for obtaining high efficiencies. In a first cell run, we demonstrate the feasibility of this concept, however, the actual cell efficiency of 20.3% is not limited by the TiOx layer selectivity, but by a reduced short-circuit current density Jsc and an increased series resistance Rs. By varying the metallization grid design on the front side, a series resistance of only 0.3 Ωcm2 was achieved, which directly correlates with a significant improvement in fill factor to 81.2%, clearly demonstrating that the ultrathin TiOx layer allows a good transport of majority carriers (electrons) and an effective blocking of minority carriers.
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A. Merkle, B. Min, R. Brendel, R. Peibst, S. Seren, H. Knauss, R. Nissler, J. Steffens, and B. Terheiden Atmospheric Pressure Chemical Vapor Deposition of in-Situ Doped Amorphous Silicon Layers for Passivating Contacts Inproceedings WIP (Hrsg.): Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition, 785-791, Brussels, Belgium, (2018). Abstract | Links | BibTeX | Schlagwörter: Amorphous Silicon (a-Si), APCVD, Carrier Selectivity, passivating contact, polycrystalline, Silicon (Si) Solar Cells @inproceedings{Merkle2018,
title = {Atmospheric Pressure Chemical Vapor Deposition of in-Situ Doped Amorphous Silicon Layers for Passivating Contacts}, author = {A Merkle and B Min and R Brendel and R Peibst and S Seren and H Knauss and R Nissler and J Steffens and B Terheiden}, editor = {WIP}, doi = {10.4229/35thEUPVSEC20182018-2DV.3.49}, year = {2018}, date = {2018-09-24}, booktitle = {Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition}, journal = {Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {785-791}, address = {Brussels, Belgium}, abstract = {Atmospheric Pressure Chemical Vapor Deposition (APCVD) is so far used for the deposition of doped and undoped oxides. We upgrade an industrial in-line APCVD tool from Schmid Thermal Systems and develop potential cost-effective APCVD processes for deposition of intrinsic and in-situ-doped amorphous silicon (a-Si) layers. In this work we report for the first time on in-situ phosphorus-doped n+-type and boron-doped p+-type APCVD silicon layers. For n+-type and p+-type polysilicon on oxide (POLO) junctions based on these layers we demonstrate saturation current densities J0 < 6 fA/cm², implied open circuit voltages iVoc of 721 mV and 730 mV respectively, and simultaneously low junction resistivity c of 18 mΩcm². These properties enable the implementation of these layers as carrier-selective passivating contacts in solar cells. First industrial proof-of-concept solar cells using boron-doped p+- type APCVD layers are presented. We show that the p+-type APCVD POLO junction formation is possible by firing only and present an industrial feasible cell process for its drop-in implementation in current passivated emitter and rear cell (PERC) process flow. }, keywords = {Amorphous Silicon (a-Si), APCVD, Carrier Selectivity, passivating contact, polycrystalline, Silicon (Si) Solar Cells}, pubstate = {published}, tppubtype = {inproceedings} } Atmospheric Pressure Chemical Vapor Deposition (APCVD) is so far used for the deposition of doped and undoped oxides. We upgrade an industrial in-line APCVD tool from Schmid Thermal Systems and develop potential cost-effective APCVD processes for deposition of intrinsic and in-situ-doped amorphous silicon (a-Si) layers. In this work we report for the first time on in-situ phosphorus-doped n+-type and boron-doped p+-type APCVD silicon layers. For n+-type and p+-type polysilicon on oxide (POLO) junctions based on these layers we demonstrate saturation current densities J0 < 6 fA/cm², implied open circuit voltages iVoc of 721 mV and 730 mV respectively, and simultaneously low junction resistivity c of 18 mΩcm². These properties enable the implementation of these layers as carrier-selective passivating contacts in solar cells. First industrial proof-of-concept solar cells using boron-doped p+- type APCVD layers are presented. We show that the p+-type APCVD POLO junction formation is possible by firing only and present an industrial feasible cell process for its drop-in implementation in current passivated emitter and rear cell (PERC) process flow.
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C. N. Kruse, K. Bothe, B. Lim, T. Dullweber, and R. Brendel WIP (Hrsg.): Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition, 249-253, Brussels, Belgium, (2018). Abstract | Links | BibTeX | Schlagwörter: SEGA @inproceedings{Kruse2018b,
title = {Synergistic Efficiency Gain Analyses for the Photovoltaic Community: An Easy to Use SEGA Simulation Tool for Silicon Solar Cells}, author = {C N Kruse and K Bothe and B Lim and T Dullweber and R Brendel}, editor = {WIP}, doi = {10.4229/35thEUPVSEC20182018-2AO.4.3}, year = {2018}, date = {2018-09-24}, booktitle = {Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {249-253}, address = {Brussels, Belgium}, abstract = {A synergistic efficiency gain analysis (SEGA) determines the efficiency gain to be expected when idealizing a certain cell property. Moreover, it provides valuable information about synergistic effects due to the coupling of loss mechanisms, e.g. various recombination losses. Here we introduce an easy to use simulation tool to the PV community for performing a SEGA for PERC, PERC+, PERT, and IBC silicon solar cells. The simulation tool comes with a graphical user interface. This SEGA-GUI creates the required set of input files after entering all experimental parameters, e. g. the sheet resistance and recombination current of an emitter. The SEGA-GUI then performs the simulations by running Quokka 2 and analyzes the results. Programming knowledge is not required. The SEGA-GUI is designed to help the user in finding options for efficiency improvements. In this work we analyze our 22.1%-efficient PERC+ solar cell. The SEGA-GUI can be downloaded for free from the ISFH website.}, keywords = {SEGA}, pubstate = {published}, tppubtype = {inproceedings} } A synergistic efficiency gain analysis (SEGA) determines the efficiency gain to be expected when idealizing a certain cell property. Moreover, it provides valuable information about synergistic effects due to the coupling of loss mechanisms, e.g. various recombination losses. Here we introduce an easy to use simulation tool to the PV community for performing a SEGA for PERC, PERC+, PERT, and IBC silicon solar cells. The simulation tool comes with a graphical user interface. This SEGA-GUI creates the required set of input files after entering all experimental parameters, e. g. the sheet resistance and recombination current of an emitter. The SEGA-GUI then performs the simulations by running Quokka 2 and analyzes the results. Programming knowledge is not required. The SEGA-GUI is designed to help the user in finding options for efficiency improvements. In this work we analyze our 22.1%-efficient PERC+ solar cell. The SEGA-GUI can be downloaded for free from the ISFH website.
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R. Brendel, C. Kruse, A. Merkle, and R. Peibst Screening Selective Contact Material Combinations for Novel Crystalline Si Cell Structures Inproceedings WIP (Hrsg.): Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition, 39-46, Brussels, Belgium, (2018). Abstract | Links | BibTeX | Schlagwörter: Carrier Selective Contacts, laser processing, loss analysis, poly Si, selective contact, selectivity, Silicon Solar Cell(s) @inproceedings{Brendel2018,
title = {Screening Selective Contact Material Combinations for Novel Crystalline Si Cell Structures}, author = {R Brendel and C Kruse and A Merkle and R Peibst}, editor = {WIP}, doi = {10.4229/35thEUPVSEC20182018-1AO.2.6}, year = {2018}, date = {2018-09-24}, booktitle = {Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {39-46}, address = {Brussels, Belgium}, abstract = {High efficiency crystalline Si solar cells require contacts with high carrier selectivity. This is ensured for contacts having low recombination currents as well as low contact resistances. A large variety of material systems for electron- and hole-selective contacts were measured in the literature. We screen a subset of electron- and hole-selective contacts to find promising combinations in terms of efficiency potential on the one hand and in terms of practical processes on the other hand. We use modelling of ideal Si cells with non-ideal experimental contact properties to determine the maximum efficiency and the optimized areal contact fractions for many contact combinations. Cells using a-Si and/or poly-Si contacts have the highest contact-limited efficiencies. Such cells are, however, quite different from today’s PERC technology. We therefore also look for contact combinations that have one contact type equal to the current PERC technology and identify cell structures that combine a poly-Si(n) contact with a screen-printed Al-doped contacts (PAL cells) as an attractive upgrade for the PERC technology. We also report on experimental work on building blocks for various types of PAL cells.}, keywords = {Carrier Selective Contacts, laser processing, loss analysis, poly Si, selective contact, selectivity, Silicon Solar Cell(s)}, pubstate = {published}, tppubtype = {inproceedings} } High efficiency crystalline Si solar cells require contacts with high carrier selectivity. This is ensured for contacts having low recombination currents as well as low contact resistances. A large variety of material systems for electron- and hole-selective contacts were measured in the literature. We screen a subset of electron- and hole-selective contacts to find promising combinations in terms of efficiency potential on the one hand and in terms of practical processes on the other hand. We use modelling of ideal Si cells with non-ideal experimental contact properties to determine the maximum efficiency and the optimized areal contact fractions for many contact combinations. Cells using a-Si and/or poly-Si contacts have the highest contact-limited efficiencies. Such cells are, however, quite different from today’s PERC technology. We therefore also look for contact combinations that have one contact type equal to the current PERC technology and identify cell structures that combine a poly-Si(n) contact with a screen-printed Al-doped contacts (PAL cells) as an attractive upgrade for the PERC technology. We also report on experimental work on building blocks for various types of PAL cells.
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