21.
C Hollemann; F Haase; S Schäfer; J Krügener; R Brendel; R Peibst
26.1%-efficient POLO-IBC cells: Quantification of electrical and optical loss mechanisms Artikel
In: Progress in Photovoltaics: Research and Applications, Bd. 27, Nr. 11, S. 950-958, 2019.
@article{Hollemann2019,
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 = {2019-11-01},
journal = {Progress in Photovoltaics: Research and Applications},
volume = {27},
number = {11},
pages = {950-958},
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 = {},
pubstate = {published},
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%).
22.
M Winter; S Bordihn; R Peibst; J Schmidt
Degradation and Regeneration of n+-Poly-Si on Oxide Surface Passivation under Illumination and Dark Annealing on p-Type Cz-Si Vortrag
Marseille, France, 11.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition).
@misc{Winter2019cb,
title = {Degradation and Regeneration of n+-Poly-Si on Oxide Surface Passivation under Illumination and Dark Annealing on p-Type Cz-Si},
author = {M Winter and S Bordihn and R Peibst and J Schmidt},
year = {2019},
date = {2019-09-11},
address = {Marseille, France},
abstract = {Degradation and regeneration of recombination parameters can occur in the bulk and at the surfaces of silicon solar cells. While bulk-related degradation effects have been studied quite intensively in recent years, there are only a few studies dealing with the degradation and regeneration of surface passivation, e.g. [1]. This study focuses on the time-resolved analysis of the recombination of 1.7 cm boron-doped p-type Cz-Si wafers, where the surfaces were passivated by n+ poly-Si on oxide layers exposed to a Rapid Thermal Annealing (RTA) step in a conventional firing furnace. Figure 1-a shows the evolution of the effective carrier lifetime eff during illumination with a halogen lamp at 1 sun (100 mW/cm2) at 185 °C at different injection densities n. The initial decrease (at t < 10-2 h) in eff is attributed to the activation of the boron-oxygen (BO) defect, which is subsequently permanently deactivated (until t = 0.1 h). Afterwards, a second, more pronounced degradation in eff occurs, which is completed after 30 h. In contrast to the initial BO-related degradation/regeneration (which is not observable for the high injection densities), the second degradation is obervable over the entire examined injection range. Our experiments show that a degradation in the surface passivation quality of the poly-Si on oxide layer can be made responsible for the second degradation effect. As can be seen in Figure 1-b, the saturation current density J0 increases by a factor of ~5 during the second degradation. Interestingly, as with the BO defect, also the surface passivation fully regenerates for a longer treatment and improves finally even beyond the initial state.},
note = {36th European Photovoltaic Solar Energy Conference and Exhibition},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
Degradation and regeneration of recombination parameters can occur in the bulk and at the surfaces of silicon solar cells. While bulk-related degradation effects have been studied quite intensively in recent years, there are only a few studies dealing with the degradation and regeneration of surface passivation, e.g. [1]. This study focuses on the time-resolved analysis of the recombination of 1.7 cm boron-doped p-type Cz-Si wafers, where the surfaces were passivated by n+ poly-Si on oxide layers exposed to a Rapid Thermal Annealing (RTA) step in a conventional firing furnace. Figure 1-a shows the evolution of the effective carrier lifetime eff during illumination with a halogen lamp at 1 sun (100 mW/cm2) at 185 °C at different injection densities n. The initial decrease (at t < 10-2 h) in eff is attributed to the activation of the boron-oxygen (BO) defect, which is subsequently permanently deactivated (until t = 0.1 h). Afterwards, a second, more pronounced degradation in eff occurs, which is completed after 30 h. In contrast to the initial BO-related degradation/regeneration (which is not observable for the high injection densities), the second degradation is obervable over the entire examined injection range. Our experiments show that a degradation in the surface passivation quality of the poly-Si on oxide layer can be made responsible for the second degradation effect. As can be seen in Figure 1-b, the saturation current density J0 increases by a factor of ~5 during the second degradation. Interestingly, as with the BO defect, also the surface passivation fully regenerates for a longer treatment and improves finally even beyond the initial state.
23.
R Peibst; C Kruse; S Schäfer; V Mertens; T Dullweber; R Brendel
For none, one or two polarities – how do POLO junctions fit best into industrial Si solar cells? Vortrag
Marseille, France, 10.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition).
@misc{Peibst2019c,
title = {For none, one or two polarities – how do POLO junctions fit best into industrial Si solar cells?},
author = {R Peibst and C Kruse and S Schäfer and V Mertens and T Dullweber and R Brendel},
year = {2019},
date = {2019-09-10},
address = {Marseille, France},
abstract = {The implementation of passivating contacts into industrial solar cells is an important subject of ongoing world-wide research. The evolutionary improvement of the PERC technology is a fast moving target for alternative approaches and thus any increase in process complexity has to be counterbalanced by a significant gain in efficiency. However, the difference in the efficiency potential (as compared to the projection for PERC) is moderate for most alternative cell concepts such as those with passivating contacts. This is in particular true if passivating contacts are applied only for one polarity. One possibility to address the “leaky bucket problem” on double-side contacted structures without the usage of a TCO is applying poly-Si on both polarities while the front side is structured (Boss). Here we introduce a back-junction Boss structure and an elegant process flow to realize this structure using Low Pressure Chemical Vapor Deposition (LPCVD). The process makes a strength out of the original weakness of LPCVD being a double-sided deposition. It also allows for an integration of bypass diodes within the cell. The successful experimental demonstration of the most critical process steps is reported. Cell results will be reported at the conference. We also report a systematic device simulation study, showing that the Boss structure has a significantly higher efficiency potential than projected with an evolutionary improvement of the PERC structure, as well as that for “PERC-like” structures with POLO junctions for either exclusively electron or hole collection. We also simulate a “PERT-like” structure with n+-type POLO on the rear (TOPCon, monoPoly, PERPoly, …) for comparison. At the conference, we intend to present our own works in the broad context of the work of other groups in this active research field.},
note = {36th European Photovoltaic Solar Energy Conference and Exhibition},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
The implementation of passivating contacts into industrial solar cells is an important subject of ongoing world-wide research. The evolutionary improvement of the PERC technology is a fast moving target for alternative approaches and thus any increase in process complexity has to be counterbalanced by a significant gain in efficiency. However, the difference in the efficiency potential (as compared to the projection for PERC) is moderate for most alternative cell concepts such as those with passivating contacts. This is in particular true if passivating contacts are applied only for one polarity. One possibility to address the “leaky bucket problem” on double-side contacted structures without the usage of a TCO is applying poly-Si on both polarities while the front side is structured (Boss). Here we introduce a back-junction Boss structure and an elegant process flow to realize this structure using Low Pressure Chemical Vapor Deposition (LPCVD). The process makes a strength out of the original weakness of LPCVD being a double-sided deposition. It also allows for an integration of bypass diodes within the cell. The successful experimental demonstration of the most critical process steps is reported. Cell results will be reported at the conference. We also report a systematic device simulation study, showing that the Boss structure has a significantly higher efficiency potential than projected with an evolutionary improvement of the PERC structure, as well as that for “PERC-like” structures with POLO junctions for either exclusively electron or hole collection. We also simulate a “PERT-like” structure with n+-type POLO on the rear (TOPCon, monoPoly, PERPoly, …) for comparison. At the conference, we intend to present our own works in the broad context of the work of other groups in this active research field.
24.
F Haase; C Hollemann; S Schaefer; J Kruegener; R Brendel; R Peibst
Transferring the record p-type Si POLO-IBC cell technology towards an industrial level Vortrag
Chicago, IL, USA, 20.06.2019, (46th IEEE Photovoltaic Specialist Conference (PVSC)).
@misc{Haase2019,
title = {Transferring the record p-type Si POLO-IBC cell technology towards an industrial level},
author = {F Haase and C Hollemann and S Schaefer and J Kruegener and R Brendel and R Peibst},
year = {2019},
date = {2019-06-20},
address = {Chicago, IL, USA},
abstract = {First, we evaluate the efficiency potential of our technology on p-type (B) Cz wafers using the lab-type process. We present a p-type Cz Si solar cell with an implied pseudo efficiency of 25.2 % measured before metallization. We had to reduce the thermal budget and to address the following implications: The two doped poly-Si on oxide (POLO) passivating contacts at the rear side are separated by a region of initially intrinsic (i) poly-Si. The latter is at least partially doped by lateral in-diffusion of dopants during junction formation. With increasing width of the (i) poly-Si region, the recombination at the p(i)n diode in the poly-Si decreases whereas the recombination at the (i) poly-Si/c-Si surface increases due to the bad passivation quality of the intrinsic poly-Si. As a second step, we suggest a process sequence for reducing the complexity down to that of a conventional PERC cell. This approach utilizes the Al‑BSF - a major strength of the existing p-PERC cells - and eliminates its weakness - that is the efficiency limiting emitter recombination at the front contacts - by using a POLO passivating contact. The process uses the same tools as a p-PERC cell and only adds one tool for poly-Si deposition. Our finite element simulations shows, that such a solar cell can reach an efficiency of 24.7 %},
note = {46th IEEE Photovoltaic Specialist Conference (PVSC)},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
First, we evaluate the efficiency potential of our technology on p-type (B) Cz wafers using the lab-type process. We present a p-type Cz Si solar cell with an implied pseudo efficiency of 25.2 % measured before metallization. We had to reduce the thermal budget and to address the following implications: The two doped poly-Si on oxide (POLO) passivating contacts at the rear side are separated by a region of initially intrinsic (i) poly-Si. The latter is at least partially doped by lateral in-diffusion of dopants during junction formation. With increasing width of the (i) poly-Si region, the recombination at the p(i)n diode in the poly-Si decreases whereas the recombination at the (i) poly-Si/c-Si surface increases due to the bad passivation quality of the intrinsic poly-Si. As a second step, we suggest a process sequence for reducing the complexity down to that of a conventional PERC cell. This approach utilizes the Al‑BSF - a major strength of the existing p-PERC cells - and eliminates its weakness - that is the efficiency limiting emitter recombination at the front contacts - by using a POLO passivating contact. The process uses the same tools as a p-PERC cell and only adds one tool for poly-Si deposition. Our finite element simulations shows, that such a solar cell can reach an efficiency of 24.7 %
25.
C Hollemann
>26% POLO-IBC-Solarzellen Vortrag
Falkau, Germany, 25.02.2019, (SiliconFOREST 2019).
@misc{Hollemann2019b,
title = {>26% POLO-IBC-Solarzellen},
author = {C Hollemann},
year = {2019},
date = {2019-02-25},
address = {Falkau, Germany},
note = {SiliconFOREST 2019},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
26.
F Kiefer; N Wehmeier; T Brendemühl; L Mettner; F Haase; M Holthausen; C Daeschlein; O Wunnicke; C Mader; 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).
@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 = {},
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.
27.
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; 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).
@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 = {},
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.
28.
F Haase; C Hollemann; S Schäfer; A Merkle; M Rienäcker; J Krügener; R Brendel; R Peibst
In: Solar Energy Materials and Solar Cells, Bd. 186, S. 184-193, 2018, ISSN: 0927-0248.
@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 = {},
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%.
29.
N Folchert; M Rienäcker; A A Yeo; B Min; R Peibst; R Brendel
Temperature-dependent contact resistance of carrier selective Poly-Si on oxide junctions Artikel
In: Solar Energy Materials and Solar Cells, Bd. 185, S. 425-430, 2018, ISSN: 0927-0248.
@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 = {},
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.
30.
C Klamt; M Rienäcker; F Haase; N Folchert; R Brendel; R Peibst; V Krausse; 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).
@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 = {},
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.
31.
J Krügener; F Haase; M Rienäcker; R Brendel; H J Osten; R Peibst
In: Solar Energy Materials and Solar Cells, Bd. 173, S. 85-91, 2017, ISSN: 0927-0248, (Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics).
@article{Krügener2017b,
title = {Improvement of the SRH bulk lifetime upon formation of n-type POLO junctions for 25% efficient Si solar cells},
author = {J Krügener and F Haase and M Rienäcker and R Brendel and H J Osten and R Peibst},
doi = {10.1016/j.solmat.2017.05.055},
issn = {0927-0248},
year = {2017},
date = {2017-12-01},
journal = {Solar Energy Materials and Solar Cells},
volume = {173},
pages = {85-91},
abstract = {Carrier-selective contact schemes, like polysilicon on oxide (POLO), provide low contact resistivities while preserving an excellent passivation quality. These junctions offer an important additional feature compared to a-Si/c-Si heterojunctions. We find that the formation of n-type POLO junctions lead to a huge increase of the Shockley-Read-Hall (SRH) lifetime of the substrate, a prerequisite for highly efficient solar cells. The SRH lifetime improvement can be observed for both bulk polarities and for a variety of bulk resistivities. Thus we suggest that the highly doped POLO junction getters impurities that have more or less symmetric SRH capture cross sections. We are able to achieve SRH lifetimes of > 50 ms. By applying POLO junctions to interdigitated back contact cells, we achieve cells with an efficiency of 25%.},
note = {Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Carrier-selective contact schemes, like polysilicon on oxide (POLO), provide low contact resistivities while preserving an excellent passivation quality. These junctions offer an important additional feature compared to a-Si/c-Si heterojunctions. We find that the formation of n-type POLO junctions lead to a huge increase of the Shockley-Read-Hall (SRH) lifetime of the substrate, a prerequisite for highly efficient solar cells. The SRH lifetime improvement can be observed for both bulk polarities and for a variety of bulk resistivities. Thus we suggest that the highly doped POLO junction getters impurities that have more or less symmetric SRH capture cross sections. We are able to achieve SRH lifetimes of > 50 ms. By applying POLO junctions to interdigitated back contact cells, we achieve cells with an efficiency of 25%.
32.
F Haase; F Kiefer; S Schäfer; C Kruse; J Krügener; R Brendel; R Peibst
In: Japanese Journal of Applied Physics, Bd. 56, S. 08MB15, 2017.
@article{Haase2017,
title = {Interdigitated back contact solar cells with polycrystalline silicon on oxide passivating contacts for both polarities},
author = {F Haase and F Kiefer and S Schäfer and C Kruse and J Krügener and R Brendel and R Peibst},
doi = {10.7567/JJAP.56.08MB15},
year = {2017},
date = {2017-07-07},
journal = {Japanese Journal of Applied Physics},
volume = {56},
pages = {08MB15},
abstract = {We demonstrate an independently confirmed 25.0%-efficient interdigitated back contact silicon solar cell with passivating polycrystalline silicon (poly-Si) on oxide (POLO) contacts that enable a high open circuit voltage of 723 mV. We use n-type POLO contacts with a measured saturation current density of J_0n = 4 fA cm−2 and p-type POLO contacts with J_0p = 10 fA cm−2. The textured front side and the gaps between the POLO contacts on the rear are passivated by aluminum oxide (AlOx ) with J_0AlOx = 6 fA cm−2 as measured after deposition. We analyze the recombination characteristics of our solar cells at different process steps using spatially resolved injection-dependent carrier lifetimes measured by infrared lifetime mapping. The implied pseudo-efficiency of the unmasked cell, i.e., cell and perimeter region are illuminated during measurement, is 26.2% before contact opening, 26.0% after contact opening and 25.7% for the finished cell. This reduction is due to an increase in the saturation current density of the AlO x passivation during chemical etching of the contact openings and of the rear side metallization. The difference between the implied pseudo-efficiency and the actual efficiency of 25.0% as determined by designated-area light current–voltage (I–V) measurements is due to series resistance and diffusion of excess carriers into the non-illuminated perimeter region.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We demonstrate an independently confirmed 25.0%-efficient interdigitated back contact silicon solar cell with passivating polycrystalline silicon (poly-Si) on oxide (POLO) contacts that enable a high open circuit voltage of 723 mV. We use n-type POLO contacts with a measured saturation current density of J_0n = 4 fA cm−2 and p-type POLO contacts with J_0p = 10 fA cm−2. The textured front side and the gaps between the POLO contacts on the rear are passivated by aluminum oxide (AlOx ) with J_0AlOx = 6 fA cm−2 as measured after deposition. We analyze the recombination characteristics of our solar cells at different process steps using spatially resolved injection-dependent carrier lifetimes measured by infrared lifetime mapping. The implied pseudo-efficiency of the unmasked cell, i.e., cell and perimeter region are illuminated during measurement, is 26.2% before contact opening, 26.0% after contact opening and 25.7% for the finished cell. This reduction is due to an increase in the saturation current density of the AlO x passivation during chemical etching of the contact openings and of the rear side metallization. The difference between the implied pseudo-efficiency and the actual efficiency of 25.0% as determined by designated-area light current–voltage (I–V) measurements is due to series resistance and diffusion of excess carriers into the non-illuminated perimeter region.
33.
M Rienäcker; A Merkle; U Römer; H Kohlenberg; J Krügener; R Brendel; R Peibst
In: Energy Procedia, Bd. 92, S. 412-418, 2016, ISSN: 1876-6102, (Proceedings of the 6th International Conference on Crystalline Silicon Photovoltaics (SiliconPV 2016)).
@article{Rienäcker2016c,
title = {Recombination Behavior of Photolithography-free Back Junction Back Contact Solar Cells with Carrier-selective Polysilicon on Oxide Junctions for Both Polarities},
author = {M Rienäcker and A Merkle and U Römer and H Kohlenberg and J Krügener and R Brendel and R Peibst},
doi = {10.1016/j.egypro.2016.07.121},
issn = {1876-6102},
year = {2016},
date = {2016-08-01},
journal = {Energy Procedia},
volume = {92},
pages = {412-418},
abstract = {We report on ion-implanted, inkjet patterned back junction back contact silicon solar cells with POLysilicon on Oxide (POLO) junctions for both polarities – n+ doped BSF and p+ doped emitter. The recombination behavior is investigated at two different processing stages: before and after trench separation of p+ and n+ regions within polysilicon (poly-Si). Before trench separation, we find a systematic dependence of the recombination behavior on the BSF index, i.e. the p+n+-junction meander length in the poly-Si. Obviously, recombination at the p+n+-junction in the poly-Si limits the implied open circuit voltage Voc,impl. at one sun illumination and the implied pseudo fill factor pFFimpl. to 695 mV and 80%, respectively. After trench isolation, however, Voc,impl (pFFimpl.) values increase up to 730 mV (85.5%), corresponding to a pseudo-efficiency of 26.2% for an assumed short circuit current density Jsc of 42 mA/cm2. We demonstrate a photolithography-free back junction back contacted solar cell with p-type and n-type POLO junctions with an in-house measured champion efficiency of 23.9% on a designated area of 3.97 cm2. This efficiency is mainly limited by the imperfect passivation in the undoped trench regions and at the undoped front side.},
note = {Proceedings of the 6th International Conference on Crystalline Silicon Photovoltaics (SiliconPV 2016)},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report on ion-implanted, inkjet patterned back junction back contact silicon solar cells with POLysilicon on Oxide (POLO) junctions for both polarities – n+ doped BSF and p+ doped emitter. The recombination behavior is investigated at two different processing stages: before and after trench separation of p+ and n+ regions within polysilicon (poly-Si). Before trench separation, we find a systematic dependence of the recombination behavior on the BSF index, i.e. the p+n+-junction meander length in the poly-Si. Obviously, recombination at the p+n+-junction in the poly-Si limits the implied open circuit voltage Voc,impl. at one sun illumination and the implied pseudo fill factor pFFimpl. to 695 mV and 80%, respectively. After trench isolation, however, Voc,impl (pFFimpl.) values increase up to 730 mV (85.5%), corresponding to a pseudo-efficiency of 26.2% for an assumed short circuit current density Jsc of 42 mA/cm2. We demonstrate a photolithography-free back junction back contacted solar cell with p-type and n-type POLO junctions with an in-house measured champion efficiency of 23.9% on a designated area of 3.97 cm2. This efficiency is mainly limited by the imperfect passivation in the undoped trench regions and at the undoped front side.