Publications
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K. VanSant, E. Warren, M. Rienäcker, H. Schulte-Huxel, R. Peibst, J. Geisz, P. Stradins, and A. Tamboli Performance Comparison of III-V//Si Tandem Solar Cells in the Three-Terminal Configuration Presentation/Poster Boston, USA, 04.12.2019, (2019 MRS Fall Meeting & Exhibit). Abstract | BibTeX | Tags: Tandem @misc{VanSant2019b,
title = {Performance Comparison of III-V//Si Tandem Solar Cells in the Three-Terminal Configuration}, author = {K VanSant and E Warren and M Rienäcker and H Schulte-Huxel and R Peibst and J Geisz and P Stradins and A Tamboli}, year = {2019}, date = {2019-12-04}, address = {Boston, USA}, abstract = {Multi-junction solar cells are a key pathway towards achieving higher photovoltaic efficiencies.The theoretical efficiency limit of a single-junction (1J) Si solar cell is 29.6%1, whereas efficiencies >32% have already been achieved for 1J III-V top cells stacked on Si bottom cells in both the two terminal (2T) and four terminal (4T) configurations.2,3 We will present a third path towards achieving efficiencies >32% with mechanically-stacked III-V-on-Si (III-V//Si) tandem solar cells using a three terminal (3T) configuration. The typical tandem device architectures either connect the sub-cells in series in a 2T configuration, or operate the stacked sub-cells independently, which requires four terminals (4T). Both configurations, however, have considerable drawbacks. The 2T configuration requires that the sub-cells are current matched to operate efficiently and so this narrowly constrains the choice of the sub-cell materials. The 4T configuration does not require sub-cell current matching but this design prohibits the possibility of monolithic growth and necessitates the inclusion of gridlines or a lateral conduction layer at the back of the top cell which reduces the transmission of light to the bottom cell.4The 3T configuration is a hybrid approach devised to address the constraints of the other two. The additional contact associated with the interdigitated back contact (IBC) Si bottom cell enables extraction or injection of current which circumvents the need for current matching between the sub-cells. The 3T design does not require an intermediate grid and is potentially compatible with both mechanical stacking, if a transparent conductive adhesive (TCA) is used, or monolithic growth. Moreover, simulations predict that 3T tandem cells could achieve efficiencies over 32%, comparable to record 4T tandem cell efficiencies.3,4We have fabricated and measured 3T mechanically-stacked III-V-on-Si (III-V//Si) tandem solar cells and will present an overview of how a 3T tandem solar cell operates. We will compare the JV and QE characteristics of a GaInP//Si tandem cell to a GaAs//Si tandem cell and analyze how the performance between these two 3T tandem solar cells differ, depending on which sub-cell is current limiting. }, note = {2019 MRS Fall Meeting & Exhibit}, keywords = {Tandem}, pubstate = {published}, tppubtype = {presentation} } Multi-junction solar cells are a key pathway towards achieving higher photovoltaic efficiencies.The theoretical efficiency limit of a single-junction (1J) Si solar cell is 29.6%1, whereas efficiencies >32% have already been achieved for 1J III-V top cells stacked on Si bottom cells in both the two terminal (2T) and four terminal (4T) configurations.2,3 We will present a third path towards achieving efficiencies >32% with mechanically-stacked III-V-on-Si (III-V//Si) tandem solar cells using a three terminal (3T) configuration. The typical tandem device architectures either connect the sub-cells in series in a 2T configuration, or operate the stacked sub-cells independently, which requires four terminals (4T). Both configurations, however, have considerable drawbacks. The 2T configuration requires that the sub-cells are current matched to operate efficiently and so this narrowly constrains the choice of the sub-cell materials. The 4T configuration does not require sub-cell current matching but this design prohibits the possibility of monolithic growth and necessitates the inclusion of gridlines or a lateral conduction layer at the back of the top cell which reduces the transmission of light to the bottom cell.4The 3T configuration is a hybrid approach devised to address the constraints of the other two. The additional contact associated with the interdigitated back contact (IBC) Si bottom cell enables extraction or injection of current which circumvents the need for current matching between the sub-cells. The 3T design does not require an intermediate grid and is potentially compatible with both mechanical stacking, if a transparent conductive adhesive (TCA) is used, or monolithic growth. Moreover, simulations predict that 3T tandem cells could achieve efficiencies over 32%, comparable to record 4T tandem cell efficiencies.3,4We have fabricated and measured 3T mechanically-stacked III-V-on-Si (III-V//Si) tandem solar cells and will present an overview of how a 3T tandem solar cell operates. We will compare the JV and QE characteristics of a GaInP//Si tandem cell to a GaAs//Si tandem cell and analyze how the performance between these two 3T tandem solar cells differ, depending on which sub-cell is current limiting.
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R. Whitehead, K. VanSant, M. Rienäcker, H. Schulte-Huxel, R. Peibst, J. Geisz, and A. Tamboli Optimizing the top cell absorbing layer thickness in 4T GaAs on Si tandem solar cells Presentation/Poster Boston, USA, 03.12.2019, (2019 MRS Fall Meeting & Exhibit). Abstract | BibTeX | Tags: Tandem @misc{Whitehead2019,
title = {Optimizing the top cell absorbing layer thickness in 4T GaAs on Si tandem solar cells}, author = {R Whitehead and K VanSant and M Rienäcker and H Schulte-Huxel and R Peibst and J Geisz and A Tamboli}, year = {2019}, date = {2019-12-03}, address = {Boston, USA}, abstract = {One method to improve silicon solar cell efficiency is to stack a silicon cell beneath a wide-bandgap top cell. To improve the overall tandem cell efficiency from that of silicon alone, the top cell material should have a higher spectral efficiency than silicon for the wavelengths of light within the top cell’s bandgap. GaAs is currently the material with the highest recorded cell efficiency for a single junction cell, at 29.1% efficiency. GaAs also has a theoretical and realized spectral efficiency higher than that of silicon between the wavelengths of 360-860 nm. Our team was able to exploit these GaAs attributes to obtain a record efficiency of 32.8% for a mechanically-stacked rear heterojunction (RHJ) GaAs-on-Si (GaAs//Si) tandem cell designed to operate in the 4-terminal (4T) (i.e. optically coupled but electrically independent) configuration. The purpose of this study is to further optimize the GaAs emitter layer thickness to maximize the efficiency of the 4T GaAs//Si tandem cells. Our record 4T GaAs//Si tandem solar cell was achieved using a 2 μm GaAs emitter layer but subsequent optical modeling of the 4T GaAs//Si tandem solar cells suggests that a slightly thicker emitter could potentially lead to even better top cell efficiencies. In addition, NREL began a collaboration with ISFH that provides high-efficiency interdigitated back contact (IBC) solar cells that could further improve the tandem cell efficiencies, when used as the Si bottom cell in the 4T GaAs//Si cell. Our un-certified current-voltage (I-V) results show an efficiency increase of 0.43% (absolute) by increasing the emitter thickness from 2.0 μm to 2.8 μm. The tandem cells are currently pending cell certification but the results for the GaAs//Si tandem cell with an emitter thickness of 2.8 μm is expected to be >32% and could potentially exceed the existing record efficiency. We will present the results of modeling the GaAs emitter thickness using modified Hovel equations that estimates the Jsc, based upon light absorption and carrier recombination. We will compare these modeled predictions to the NREL-certified I-V and external quantum efficiency (EQE) results obtained from 4T GaAs//Si tandem cells fabricated with absorber layer thicknesses varying from 1.5 to 3.5 μm. We will also compare the performance of our 4T GaAs//Si tandem cells to the record 4T GaAs//Si tandem cell efficiency of 32.8%.}, note = {2019 MRS Fall Meeting & Exhibit}, keywords = {Tandem}, pubstate = {published}, tppubtype = {presentation} } One method to improve silicon solar cell efficiency is to stack a silicon cell beneath a wide-bandgap top cell. To improve the overall tandem cell efficiency from that of silicon alone, the top cell material should have a higher spectral efficiency than silicon for the wavelengths of light within the top cell’s bandgap. GaAs is currently the material with the highest recorded cell efficiency for a single junction cell, at 29.1% efficiency. GaAs also has a theoretical and realized spectral efficiency higher than that of silicon between the wavelengths of 360-860 nm. Our team was able to exploit these GaAs attributes to obtain a record efficiency of 32.8% for a mechanically-stacked rear heterojunction (RHJ) GaAs-on-Si (GaAs//Si) tandem cell designed to operate in the 4-terminal (4T) (i.e. optically coupled but electrically independent) configuration. The purpose of this study is to further optimize the GaAs emitter layer thickness to maximize the efficiency of the 4T GaAs//Si tandem cells. Our record 4T GaAs//Si tandem solar cell was achieved using a 2 μm GaAs emitter layer but subsequent optical modeling of the 4T GaAs//Si tandem solar cells suggests that a slightly thicker emitter could potentially lead to even better top cell efficiencies. In addition, NREL began a collaboration with ISFH that provides high-efficiency interdigitated back contact (IBC) solar cells that could further improve the tandem cell efficiencies, when used as the Si bottom cell in the 4T GaAs//Si cell. Our un-certified current-voltage (I-V) results show an efficiency increase of 0.43% (absolute) by increasing the emitter thickness from 2.0 μm to 2.8 μm. The tandem cells are currently pending cell certification but the results for the GaAs//Si tandem cell with an emitter thickness of 2.8 μm is expected to be >32% and could potentially exceed the existing record efficiency. We will present the results of modeling the GaAs emitter thickness using modified Hovel equations that estimates the Jsc, based upon light absorption and carrier recombination. We will compare these modeled predictions to the NREL-certified I-V and external quantum efficiency (EQE) results obtained from 4T GaAs//Si tandem cells fabricated with absorber layer thicknesses varying from 1.5 to 3.5 μm. We will also compare the performance of our 4T GaAs//Si tandem cells to the record 4T GaAs//Si tandem cell efficiency of 32.8%.
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S. Kajari-Schroder, C. Gemmel, J. Hensen, J. Strey, and R. Brendel High-Quality Kerfless Wafers from the Porous Silicon Layer Transfer Process Presentation/Poster Boston, USA, 02.12.2019, (2019 MRS Fall Meeting & Exhibit). Abstract | BibTeX | Tags: kerfless @misc{Kajari-Schroder2019b,
title = {High-Quality Kerfless Wafers from the Porous Silicon Layer Transfer Process}, author = {S Kajari-Schroder and C Gemmel and J Hensen and J Strey and R Brendel}, year = {2019}, date = {2019-12-02}, address = {Boston, USA}, abstract = {Silicon wafers constitute a significant cost factor in solar cell and module manufacturing. The porous silicon (PSI) layer transfer process is a kerfless wafering technique that allows for a drastically reduced material and energy consumption per wafer and thus has great potential to reduce the wafer cost. In this process, a thick, highly p-doped substrate is electrochemically porosified, reorganized at high temperature and used as a growth substrate for silicon epitaxy. The epitaxial layer can subsequently be lifted off and the substrate wafer is reused. Key requirements for the realization of this potential in PV industry are, amongst others, a high lift-off yield of the epitaxial wafers from the porosified growth substrate, a robust process sequence, and a high electronic quality at the level of wire-cut Cz wafers. Furthermore, the kerfless wafers should be readily usable in standard solar cell manufacturing equipment, providing drop-in replacement wafers for PV industry. Here, we summarize the recent progress demonstrating several of these key aspects: first, we show that the PSI process is robust with respect to a moderate variation of processing parameters. In high-volume production, it is desirable to use e.g. a typical range of growth substrate resistivities and to use an electrolyte for the porosification process for an extended time. Both conditions would lead to a varying porosity of the growth substrate. We simulate this by a controlled variation of etching parameters, which also results in a variation of porosities in the growth substrate. We find a) that the lifetime of the PSI wafers is independent of the growth substrate separation layer porosities and b) that a reasonable process window in terms of the etching current density can be found. Second, we discuss the statistical evaluation of a large set of epitaxial runs with respect to the process yield: we are able to achieve lift-off of 59 out of 62 PSI wafers, which demonstrates a lift-off yield of the PSI process within our rigorously defined process window of at least 88 % with an error probability of 5 %. Finally, we show that high minority carrier lifetimes of up to 4.3 ms on n-type PSI wafers are achievable right after the epitaxy process, and that these lifetimes can be increased either by phosphorous diffusion gettering or by gettering with a n-type polysilicon on oxide (POLO) junction to up to 8 ms. With this, the PSI wafers are on par with standard PV wafers regarding the electronic quality.}, note = {2019 MRS Fall Meeting & Exhibit}, keywords = {kerfless}, pubstate = {published}, tppubtype = {presentation} } Silicon wafers constitute a significant cost factor in solar cell and module manufacturing. The porous silicon (PSI) layer transfer process is a kerfless wafering technique that allows for a drastically reduced material and energy consumption per wafer and thus has great potential to reduce the wafer cost. In this process, a thick, highly p-doped substrate is electrochemically porosified, reorganized at high temperature and used as a growth substrate for silicon epitaxy. The epitaxial layer can subsequently be lifted off and the substrate wafer is reused. Key requirements for the realization of this potential in PV industry are, amongst others, a high lift-off yield of the epitaxial wafers from the porosified growth substrate, a robust process sequence, and a high electronic quality at the level of wire-cut Cz wafers. Furthermore, the kerfless wafers should be readily usable in standard solar cell manufacturing equipment, providing drop-in replacement wafers for PV industry. Here, we summarize the recent progress demonstrating several of these key aspects: first, we show that the PSI process is robust with respect to a moderate variation of processing parameters. In high-volume production, it is desirable to use e.g. a typical range of growth substrate resistivities and to use an electrolyte for the porosification process for an extended time. Both conditions would lead to a varying porosity of the growth substrate. We simulate this by a controlled variation of etching parameters, which also results in a variation of porosities in the growth substrate. We find a) that the lifetime of the PSI wafers is independent of the growth substrate separation layer porosities and b) that a reasonable process window in terms of the etching current density can be found. Second, we discuss the statistical evaluation of a large set of epitaxial runs with respect to the process yield: we are able to achieve lift-off of 59 out of 62 PSI wafers, which demonstrates a lift-off yield of the PSI process within our rigorously defined process window of at least 88 % with an error probability of 5 %. Finally, we show that high minority carrier lifetimes of up to 4.3 ms on n-type PSI wafers are achievable right after the epitaxy process, and that these lifetimes can be increased either by phosphorous diffusion gettering or by gettering with a n-type polysilicon on oxide (POLO) junction to up to 8 ms. With this, the PSI wafers are on par with standard PV wafers regarding the electronic quality.
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D. Hinken, I. Kröger, S. Winter, R. Brendel, and K. Bothe Determining the spectral responsivity of solar cells under standard test conditions Journal Article Measurement Science and Technology 30 (12), 125008, (2019). Abstract | Links | BibTeX | Tags: @article{Hinken2019,
title = {Determining the spectral responsivity of solar cells under standard test conditions}, author = {D Hinken and I Kröger and S Winter and R Brendel and K Bothe}, doi = {10.1088/1361-6501/ab34ef}, year = {2019}, date = {2019-12-01}, journal = {Measurement Science and Technology}, volume = {30}, number = {12}, pages = {125008}, publisher = {IOP Publishing}, abstract = {The spectral responsivity of solar cells is widely used for cell analysis or calibration purposes. According to the IEC60904-8:2014 standard, the reference method for the determination of is the complete differential spectral responsivity approach. For this approach, the differential spectral responsivity is measured as a function of wavelength and bias irradiance. To obtain the spectral responsivity related to standard test conditions the IEC60904-8:2014 standard recommends to integrate via bias current for each wavelength. We show that this integration is wrong. It lacks analytical derivation and provides faulty curves for non-linear solar cells. We prove analytically and by means of simulations that the correct way of calculation is either the integration of via the bias irradiance or the integration of via the bias current , with being the AMx-weighted (e.g. AM1.5G or AM1.5D) differential responsivity. A simulation of the differential spectral responsivity of a strongly non-linear solar cell demonstrates deviations of up to 30% for (the wrong) integration of via at some wavelengths, corresponding to a deviation in the short-circuit current of up to 3.0%.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The spectral responsivity of solar cells is widely used for cell analysis or calibration purposes. According to the IEC60904-8:2014 standard, the reference method for the determination of is the complete differential spectral responsivity approach. For this approach, the differential spectral responsivity is measured as a function of wavelength and bias irradiance. To obtain the spectral responsivity related to standard test conditions the IEC60904-8:2014 standard recommends to integrate via bias current for each wavelength. We show that this integration is wrong. It lacks analytical derivation and provides faulty curves for non-linear solar cells. We prove analytically and by means of simulations that the correct way of calculation is either the integration of via the bias irradiance or the integration of via the bias current , with being the AMx-weighted (e.g. AM1.5G or AM1.5D) differential responsivity. A simulation of the differential spectral responsivity of a strongly non-linear solar cell demonstrates deviations of up to 30% for (the wrong) integration of via at some wavelengths, corresponding to a deviation in the short-circuit current of up to 3.0%.
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R. Reineke-Koch Überhitzungsschutz für Solarkollektoren – neue Lösungswege Presentation/Poster Bern, Switzerland, 29.11.2019. BibTeX | Tags: Kollektoren @misc{Reineke-Koch2019,
title = {Überhitzungsschutz für Solarkollektoren – neue Lösungswege}, author = {R Reineke-Koch}, year = {2019}, date = {2019-11-29}, address = {Bern, Switzerland}, keywords = {Kollektoren}, pubstate = {published}, tppubtype = {presentation} } |
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F. Weiland, M. Kirchner, V. Rensinghoff, F. Giovannetti, O. Kastner, D. Ridder, Y. Tekinbas, and H. Hachul Performance assessment of solar thermally activated steel sandwich panels with mineral wool core for industrial and commercial buildings Journal Article Journal of Physics: Conference Series 1343 , 012098, (2019). Abstract | Links | BibTeX | Tags: @article{Weiland2019b,
title = {Performance assessment of solar thermally activated steel sandwich panels with mineral wool core for industrial and commercial buildings}, author = {F Weiland and M Kirchner and V Rensinghoff and F Giovannetti and O Kastner and D Ridder and Y Tekinbas and H Hachul}, doi = {10.1088/1742-6596/1343/1/012098}, year = {2019}, date = {2019-11-20}, journal = {Journal of Physics: Conference Series}, volume = {1343}, pages = {012098}, publisher = {IOP Publishing}, abstract = {Steel sandwich panels are well established, cost effective components for the construction of structural and functional envelopes in buildings. They offer not only design flexibility but also great potential for active solar energy use. This contribution investigates the performance of solar thermal active panels with mineral wool core featuring heat exchangers comprising different designs and materials by means of FEM simulations. The simulation model is validated against measurements of fabricated test specimen. Specific results are reported for a large-sized test specimen with a grey finishing (RAL 7043) where the conversion factor η0 ranges between 0.46 and 0.56. The results imply that higher figures of 0.73 and higher are theoretically achievable with a more efficient use of the panel area and improved manufacturing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Steel sandwich panels are well established, cost effective components for the construction of structural and functional envelopes in buildings. They offer not only design flexibility but also great potential for active solar energy use. This contribution investigates the performance of solar thermal active panels with mineral wool core featuring heat exchangers comprising different designs and materials by means of FEM simulations. The simulation model is validated against measurements of fabricated test specimen. Specific results are reported for a large-sized test specimen with a grey finishing (RAL 7043) where the conversion factor η0 ranges between 0.46 and 0.56. The results imply that higher figures of 0.73 and higher are theoretically achievable with a more efficient use of the panel area and improved manufacturing.
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R. Peibst, C. Kruse, S. Schäfer, V. Mertens, S. Bordihn, T. Dullweber, F. Haase, C. Hollemann, B. Lim, B. Min, R. Niepelt, H. Schulte-Huxel, and R. Brendel For none, one, or two polarities—How do POLO junctions fit best into industrial Si solar cells? Journal Article Forthcoming Progress in Photovoltaics: Research and Applications Forthcoming. Abstract | Links | BibTeX | Tags: efficiency potential, passivating contacts, POLO, Poly-Si, solar cell development @article{Peibst2019f,
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 S Bordihn and T Dullweber and F Haase and C Hollemann and B Lim and B Min and R Niepelt and H Schulte-Huxel and R Brendel}, doi = {10.1002/pip.3201}, year = {2019}, date = {2019-11-05}, journal = {Progress in Photovoltaics: Research and Applications}, abstract = {Abstract We present a systematic study on the benefit of the implementation of poly-Si on oxide (POLO) or related junctions into p-type industrial Si solar cells as compared with the benchmark of Passivated Emitter and Rear Cell (PERC). We assess three aspects: (a) the simulated efficiency potential of representative structures with POLO junctions for none (=PERC+), one, and for two polarities; (b) possible lean process flows for their fabrication; and (c) experimental results on major building blocks. Synergistic efficiency gain analysis reveals that the exclusive suppression of the contact recombination for one polarity by POLO only yields moderate efficiency improvements between 0.23%abs and 0.41%abs as compared with PERC+ because of the remaining recombination paths. This problem is solved in a structure that includes POLO junctions for both polarities (POLO2), for whose realization we propose a lean process flow, and for which we experimentally demonstrate the most important building blocks. However, two experimental challenges—alignment tolerances and screen-print metallization of p+ poly-Si—are unsolved so far and reduced the efficiency of the “real” POLO2 cell as compared with an idealized scenario. As an intermediate step, we therefore work on a POLO IBC cell with POLO junctions for one polarity. It avoids the abovementioned challenges of the POLO2 structure, can be realized within a lean process flow, and has an efficiency benefit of 1.59%abs as compared with PERC—because not only contact recombination is suppressed but also the entire phosphorus emitter is replaced by an n+ POLO junction.}, keywords = {efficiency potential, passivating contacts, POLO, Poly-Si, solar cell development}, pubstate = {forthcoming}, tppubtype = {article} } Abstract We present a systematic study on the benefit of the implementation of poly-Si on oxide (POLO) or related junctions into p-type industrial Si solar cells as compared with the benchmark of Passivated Emitter and Rear Cell (PERC). We assess three aspects: (a) the simulated efficiency potential of representative structures with POLO junctions for none (=PERC+), one, and for two polarities; (b) possible lean process flows for their fabrication; and (c) experimental results on major building blocks. Synergistic efficiency gain analysis reveals that the exclusive suppression of the contact recombination for one polarity by POLO only yields moderate efficiency improvements between 0.23%abs and 0.41%abs as compared with PERC+ because of the remaining recombination paths. This problem is solved in a structure that includes POLO junctions for both polarities (POLO2), for whose realization we propose a lean process flow, and for which we experimentally demonstrate the most important building blocks. However, two experimental challenges—alignment tolerances and screen-print metallization of p+ poly-Si—are unsolved so far and reduced the efficiency of the “real” POLO2 cell as compared with an idealized scenario. As an intermediate step, we therefore work on a POLO IBC cell with POLO junctions for one polarity. It avoids the abovementioned challenges of the POLO2 structure, can be realized within a lean process flow, and has an efficiency benefit of 1.59%abs as compared with PERC—because not only contact recombination is suppressed but also the entire phosphorus emitter is replaced by an n+ POLO junction.
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M. Schnabel, H. Schulte-Huxel, M. Rienäcker, E. L. Warren, P. F. Ndione, B. Nemeth, T. R. Klein, M. F. A. M. van Hest, J. F. Geisz, R. Peibst, P. Stradins, and A. C. Tamboli Three-terminal III–V/Si tandem solar cells enabled by a transparent conductive adhesive Journal Article Forthcoming Sustainable Energy Fuels -, Forthcoming. Abstract | Links | BibTeX | Tags: @article{Schnabel2019,
title = {Three-terminal III–V/Si tandem solar cells enabled by a transparent conductive adhesive}, author = {M Schnabel and H Schulte-Huxel and M Rienäcker and E L Warren and P F Ndione and B Nemeth and T R Klein and M F A M van Hest and J F Geisz and R Peibst and P Stradins and A C Tamboli}, doi = {10.1039/C9SE00893D}, year = {2019}, date = {2019-11-04}, journal = {Sustainable Energy Fuels}, pages = {-}, publisher = {The Royal Society of Chemistry}, abstract = {Tandem or multijunction solar cells are able to convert sunlight to electricity with greater efficiency than single junction solar cells by splitting the solar spectrum across sub-cells with different bandgaps. With the efficiencies of many common single-junction solar cell materials leveling off near their theoretical efficiency limits, there is renewed interest in applying this approach. However, there is ongoing debate as to the best approach for interconnecting sub-cells in series, or whether it is preferable to operate them independently. In this paper, we provide the first experimental demonstration of a tandem cell architecture with three terminals: one on top of the tandem cell, and two beneath it, in interdigitated back contact configuration. The two cells are interconnected with a transparent conductive adhesive, which is compatible with rough surfaces and exhibits negligible series resistance. Combining GaInP and Si sub-cells in this manner allows us to achieve a GaInP/Si tandem cell with a two-terminal efficiency of 26.4 ± 1.0%. We then show that utilizing all three terminals results in an efficiency boost of 0.9 ± 0.2%, to an efficiency of 27.3 ± 1.0%, and discuss the operation of the cell and its two interacting circuits.}, keywords = {}, pubstate = {forthcoming}, tppubtype = {article} } Tandem or multijunction solar cells are able to convert sunlight to electricity with greater efficiency than single junction solar cells by splitting the solar spectrum across sub-cells with different bandgaps. With the efficiencies of many common single-junction solar cell materials leveling off near their theoretical efficiency limits, there is renewed interest in applying this approach. However, there is ongoing debate as to the best approach for interconnecting sub-cells in series, or whether it is preferable to operate them independently. In this paper, we provide the first experimental demonstration of a tandem cell architecture with three terminals: one on top of the tandem cell, and two beneath it, in interdigitated back contact configuration. The two cells are interconnected with a transparent conductive adhesive, which is compatible with rough surfaces and exhibits negligible series resistance. Combining GaInP and Si sub-cells in this manner allows us to achieve a GaInP/Si tandem cell with a two-terminal efficiency of 26.4 ± 1.0%. We then show that utilizing all three terminals results in an efficiency boost of 0.9 ± 0.2%, to an efficiency of 27.3 ± 1.0%, and discuss the operation of the cell and its two interacting circuits.
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F. Giovannetti Experimental Investigations on Photovoltaic-Thermal Arrays Designed for the Use as Heat Pump Source Presentation/Poster Santiago, Chile, 04.11.2019, (ISES Solar World Congress and IEA Solar Heating and Cooling (SHC) Conference). @misc{Giovannetti2019c,
title = {Experimental Investigations on Photovoltaic-Thermal Arrays Designed for the Use as Heat Pump Source}, author = {F Giovannetti}, year = {2019}, date = {2019-11-04}, address = {Santiago, Chile}, note = {ISES Solar World Congress and IEA Solar Heating and Cooling (SHC) Conference}, keywords = {PVT}, pubstate = {published}, tppubtype = {presentation} } |
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F. Giovannetti Improved flat plate collector with heat pipes for overheating prevention in solar thermal systems Presentation/Poster Santiago, Chile, 04.11.2019, (ISES Solar World Congress and IEA Solar Heating and Cooling (SHC) Conference). BibTeX | Tags: Solar thermal @misc{Giovannetti2019d,
title = {Improved flat plate collector with heat pipes for overheating prevention in solar thermal systems}, author = {F Giovannetti}, year = {2019}, date = {2019-11-04}, address = {Santiago, Chile}, note = {ISES Solar World Congress and IEA Solar Heating and Cooling (SHC) Conference}, keywords = {Solar thermal}, pubstate = {published}, tppubtype = {presentation} } |
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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 Journal Article Progress in Photovoltaics: Research and Applications 27 (11), 950-958, (2019). Abstract | Links | BibTeX | Tags: efficiency potential, IBC solar cells, lifetime monitoring, passivating contacts, POLO @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 = {efficiency potential, IBC solar cells, lifetime monitoring, passivating contacts, POLO}, 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%).
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C. Gemmel, J. Hensen, S. Kajari-Schröder, and R. Brendel Detachment yield statistics for kerfless wafering using the porous silicon process Journal Article Solar Energy Materials and Solar Cells 202 , 110061, (2019), ISSN: 0927-0248. Abstract | Links | BibTeX | Tags: Detachment probability, Porous silicon process, Statistical evaluation, Yield @article{Gemmel2019c,
title = {Detachment yield statistics for kerfless wafering using the porous silicon process}, author = {C Gemmel and J Hensen and S Kajari-Schröder and R Brendel}, doi = {10.1016/j.solmat.2019.110061}, issn = {0927-0248}, year = {2019}, date = {2019-11-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {202}, pages = {110061}, abstract = {The porous silicon (PSI) process is a wafering method to fabricate high quality kerfless crystalline Si wafers by epitaxial wafer growth on porous Si and subsequent detachment from a reusable substrate wafer. The process yield is a key parameter for the economic viability of the PSI process. We experimentally demonstrate the detachment of 59 out of 62 PSI wafers with a size of 10 × 10 cm2, and separation layer etch current densities of 105–120 mA/cm2 for electrochemically etching the porous Si, and for substrate wafers with a resistivity of 15.7–16.9 mΩcm. We discuss the statistics of how to deduce a detachment probability from this. From our experiments, we determine a detachment yield of at least 88% with an error probability of 5%. The demonstration of a 99% detachment yield with an error probability of 5% would require at least 300 successfully detached wafers with no failed detachment. Samples have a minority carrier density ranging from 1 to 1.7 ms before any external gettering, which demonstrates the high electric quality of the PSI wafers.}, keywords = {Detachment probability, Porous silicon process, Statistical evaluation, Yield}, pubstate = {published}, tppubtype = {article} } The porous silicon (PSI) process is a wafering method to fabricate high quality kerfless crystalline Si wafers by epitaxial wafer growth on porous Si and subsequent detachment from a reusable substrate wafer. The process yield is a key parameter for the economic viability of the PSI process. We experimentally demonstrate the detachment of 59 out of 62 PSI wafers with a size of 10 × 10 cm2, and separation layer etch current densities of 105–120 mA/cm2 for electrochemically etching the porous Si, and for substrate wafers with a resistivity of 15.7–16.9 mΩcm. We discuss the statistics of how to deduce a detachment probability from this. From our experiments, we determine a detachment yield of at least 88% with an error probability of 5%. The demonstration of a 99% detachment yield with an error probability of 5% would require at least 300 successfully detached wafers with no failed detachment. Samples have a minority carrier density ranging from 1 to 1.7 ms before any external gettering, which demonstrates the high electric quality of the PSI wafers.
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L. Helmich, D. C. Walter, and J. Schmidt Direct Examination of the Deactivation of the Boron–Oxygen Center in Cz-Si Solar Cells Under Regeneration Conditions via Electroluminescence Journal Article IEEE Journal of Photovoltaics 9 (6), 1472-1476, (2019), ISSN: 2156-3381. Abstract | Links | BibTeX | Tags: boron–oxygen defect, carrier injection, Czochralski-grown silicon, electroluminescence (EL), light-induced degradation (LID), passivated emitter and rear cells (PERCs), regeneration @article{Helmich2019b,
title = {Direct Examination of the Deactivation of the Boron–Oxygen Center in Cz-Si Solar Cells Under Regeneration Conditions via Electroluminescence}, author = {L Helmich and D C Walter and J Schmidt}, doi = {10.1109/JPHOTOV.2019.2926855}, issn = {2156-3381}, year = {2019}, date = {2019-11-01}, journal = {IEEE Journal of Photovoltaics}, volume = {9}, number = {6}, pages = {1472-1476}, abstract = {We examine the regeneration kinetics of the boron–oxygen defect in boron-doped p-type Czochralski-grown silicon (Cz-Si) solar cells as a function of the excess carrier concentration Δn at the regeneration conditions, i.e., at elevated temperature (140 °C). To perform the regeneration, we apply different forward-bias voltages (V$_rm appl$) to solar cells in darkness and measure directly the emitted electroluminescence (EL) signal at different time steps during the regeneration of the cell. Measuring the EL signal emitted by the solar cell during regeneration, we are able to directly determine Δn during regeneration for each applied voltage. In addition to the EL signal, we measure the electric current flowing through the solar cell during the regeneration process. This current is proportional to the overall recombination rate in the cell and, hence, reflects the changing bulk recombination during the regeneration process. From the measured time-dependent cell current, we determine the deactivation rate constant R$_rm de$ of the boron–oxygen defect. Our experimental results unambiguously show that R$_rm de$ increases proportionally with Δn during the regeneration process.}, keywords = {boron–oxygen defect, carrier injection, Czochralski-grown silicon, electroluminescence (EL), light-induced degradation (LID), passivated emitter and rear cells (PERCs), regeneration}, pubstate = {published}, tppubtype = {article} } We examine the regeneration kinetics of the boron–oxygen defect in boron-doped p-type Czochralski-grown silicon (Cz-Si) solar cells as a function of the excess carrier concentration Δn at the regeneration conditions, i.e., at elevated temperature (140 °C). To perform the regeneration, we apply different forward-bias voltages (V$_rm appl$) to solar cells in darkness and measure directly the emitted electroluminescence (EL) signal at different time steps during the regeneration of the cell. Measuring the EL signal emitted by the solar cell during regeneration, we are able to directly determine Δn during regeneration for each applied voltage. In addition to the EL signal, we measure the electric current flowing through the solar cell during the regeneration process. This current is proportional to the overall recombination rate in the cell and, hence, reflects the changing bulk recombination during the regeneration process. From the measured time-dependent cell current, we determine the deactivation rate constant R$_rm de$ of the boron–oxygen defect. Our experimental results unambiguously show that R$_rm de$ increases proportionally with Δn during the regeneration process.
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J. Schmidt, D. Bredemeier, and D. C. Walter On the Defect Physics Behind Light and Elevated Temperature-Induced Degradation (LeTID) of Multicrystalline Silicon Solar Cells Journal Article IEEE Journal of Photovoltaics 9 (6), 1497-1503, (2019). Abstract | Links | BibTeX | Tags: defects, Degradation, Hydrogen, metallic impurity, multicrystalline silicon (mc-Si), silicon, Solar Cells @article{Schmidt2019d,
title = {On the Defect Physics Behind Light and Elevated Temperature-Induced Degradation (LeTID) of Multicrystalline Silicon Solar Cells}, author = {J Schmidt and D Bredemeier and D C Walter}, doi = {10.1109/JPHOTOV.2019.2937223}, year = {2019}, date = {2019-11-01}, journal = {IEEE Journal of Photovoltaics}, volume = {9}, number = {6}, pages = {1497-1503}, abstract = {State-of-the-art solar cells with passivated surfaces fabricated on block-cast multicrystalline silicon (mc-Si) wafers show a pronounced degradation in efficiency under illumination at elevated temperature, as it typically occurs during operation in a solar module. This effect, frequently named `Light and elevated Temperature-Induced Degradation' (LeTID), has been attributed to the activation of a specific, hitherto unrevealed bulk defect in mc-Si. Recent experimental results of several labs have indicated that hydrogen is somehow involved in the responsible defect physics, without however providing any direct evidence so far. In this article, we present experimental data unambiguously showing a direct positive correlation of the extent of LeTID with the hydrogen content introduced into the silicon bulk during firing of the silicon wafers coated with hydrogen-rich silicon nitride (SiN$_rm x$:H) layers. Additional experiments including the pronounced impact of phosphorus gettering on the LeTID extent and the dependence of the degradation and regeneration on the wafer thickness support the involvement of a second species, with most indications pointing towards a metallic impurity. Several approaches of completely avoiding the instability in mc-Si solar cells are derived from the presented defect model, including 1) tuning of the SiN$_rm x$:H layer properties to minimize the in-diffusion of hydrogen into the wafer and 2) the thinning of the mc-Si wafer, improving the getterability of the metal impurity component toward the surfaces.}, keywords = {defects, Degradation, Hydrogen, metallic impurity, multicrystalline silicon (mc-Si), silicon, Solar Cells}, pubstate = {published}, tppubtype = {article} } State-of-the-art solar cells with passivated surfaces fabricated on block-cast multicrystalline silicon (mc-Si) wafers show a pronounced degradation in efficiency under illumination at elevated temperature, as it typically occurs during operation in a solar module. This effect, frequently named `Light and elevated Temperature-Induced Degradation' (LeTID), has been attributed to the activation of a specific, hitherto unrevealed bulk defect in mc-Si. Recent experimental results of several labs have indicated that hydrogen is somehow involved in the responsible defect physics, without however providing any direct evidence so far. In this article, we present experimental data unambiguously showing a direct positive correlation of the extent of LeTID with the hydrogen content introduced into the silicon bulk during firing of the silicon wafers coated with hydrogen-rich silicon nitride (SiN$_rm x$:H) layers. Additional experiments including the pronounced impact of phosphorus gettering on the LeTID extent and the dependence of the degradation and regeneration on the wafer thickness support the involvement of a second species, with most indications pointing towards a metallic impurity. Several approaches of completely avoiding the instability in mc-Si solar cells are derived from the presented defect model, including 1) tuning of the SiN$_rm x$:H layer properties to minimize the in-diffusion of hydrogen into the wafer and 2) the thinning of the mc-Si wafer, improving the getterability of the metal impurity component toward the surfaces.
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Y. Louvet, S. Fischer, S. Furbo, F. Giovannetti, S. Helbig, M. Köhl, D. Mugnier, D. Philippen, F. Veynandt, and K. Vajen Economic comparison of reference solar thermal systems for households in five European countries Journal Article Solar Energy 193 , 85 - 94, (2019), ISSN: 0038-092X. Abstract | Links | BibTeX | Tags: Energy economics, Solar thermal energy in Europe @article{Louvet2019b,
title = {Economic comparison of reference solar thermal systems for households in five European countries}, author = {Y Louvet and S Fischer and S Furbo and F Giovannetti and S Helbig and M Köhl and D Mugnier and D Philippen and F Veynandt and K Vajen}, doi = {10.1016/j.solener.2019.09.019}, issn = {0038-092X}, year = {2019}, date = {2019-11-01}, journal = {Solar Energy}, volume = {193}, pages = {85 - 94}, abstract = {This study presents a methodology developed in the framework of Task54 of the Solar Heating and Cooling (SHC) Program of the International Energy Agency (IEA) to calculate the heat cost per kWh final energy of solar thermal systems. Based on the concept of levelized cost of energy, three indicators are introduced depicting the heat cost of the solar part of the heating system only (LCoHsol,fin), the conventional part (LCoHconv,fin) or the overall solar assisted heating system (LCoHov,fin). The LCoHov,fin enables a comparison with other heating systems using different technologies. Applied to eleven residential systems in five European countries, the results show that the heat cost differs widely, depending on countries and system types. The solar heating system raises the heat cost of the overall solar assisted heating system compared to a reference system without solar assistance (subsidies are not considered) in most studied cases, but some solar domestic hot water systems and solar heating systems for multi-family houses are close to parity under current economic conditions and the assumptions considered in the paper. This work also highlights the importance of calculating the heat cost with a standardized methodology to enable a comparison between different systems.}, keywords = {Energy economics, Solar thermal energy in Europe}, pubstate = {published}, tppubtype = {article} } This study presents a methodology developed in the framework of Task54 of the Solar Heating and Cooling (SHC) Program of the International Energy Agency (IEA) to calculate the heat cost per kWh final energy of solar thermal systems. Based on the concept of levelized cost of energy, three indicators are introduced depicting the heat cost of the solar part of the heating system only (LCoHsol,fin), the conventional part (LCoHconv,fin) or the overall solar assisted heating system (LCoHov,fin). The LCoHov,fin enables a comparison with other heating systems using different technologies. Applied to eleven residential systems in five European countries, the results show that the heat cost differs widely, depending on countries and system types. The solar heating system raises the heat cost of the overall solar assisted heating system compared to a reference system without solar assistance (subsidies are not considered) in most studied cases, but some solar domestic hot water systems and solar heating systems for multi-family houses are close to parity under current economic conditions and the assumptions considered in the paper. This work also highlights the importance of calculating the heat cost with a standardized methodology to enable a comparison between different systems.
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A. Čampa, F. Smole, N. Folchert, T. Wietler, B. Min, R. Brendel, and M. Topič Detailed Analysis and Understanding of the Transport Mechanism of Poly-Si-Based Carrier Selective Junctions Journal Article IEEE Journal of Photovoltaics 9 (6), 1575-1582, (2019). Abstract | Links | BibTeX | Tags: Carrier-selective junctions, numerical simulations, pinholes, polysilicon on oxide, Tunneling @article{Čampa2019,
title = {Detailed Analysis and Understanding of the Transport Mechanism of Poly-Si-Based Carrier Selective Junctions}, author = {A Čampa and F Smole and N Folchert and T Wietler and B Min and R Brendel and M Topič}, doi = {10.1109/JPHOTOV.2019.2943610}, year = {2019}, date = {2019-11-01}, journal = {IEEE Journal of Photovoltaics}, volume = {9}, number = {6}, pages = {1575-1582}, abstract = {We investigate the transport mechanism of poly-Si-based carrier-selective junctions using the two-dimensional numerical semiconductor device simulations. The detailed transport model considers the charge carrier transport through the pinholes as well as tunneling through a very thin silicon oxide simultaneously. For the verification of the simulation model, the complete temperature dependent transfer length method is modeled and its results are verified with measurements of two different samples. By means of rigorous simulations, the influence of different pinhole geometrical and material parameters on junction resistivity are investigated and explained in detail. From the presented results, the fundamental understanding needed for optimizing the poly-Si-based carrier selective junction in respect to the main design parameters such as doping level in poly-Si, annealing time, silicon oxide thickness, and pinhole density is given. The detailed analysis shows the pinhole channel plays the most crucial role in the design of poly-Si-based carrier-selective junctions if the silicon oxide layer thickness is larger than 2 nm.}, keywords = {Carrier-selective junctions, numerical simulations, pinholes, polysilicon on oxide, Tunneling}, pubstate = {published}, tppubtype = {article} } We investigate the transport mechanism of poly-Si-based carrier-selective junctions using the two-dimensional numerical semiconductor device simulations. The detailed transport model considers the charge carrier transport through the pinholes as well as tunneling through a very thin silicon oxide simultaneously. For the verification of the simulation model, the complete temperature dependent transfer length method is modeled and its results are verified with measurements of two different samples. By means of rigorous simulations, the influence of different pinhole geometrical and material parameters on junction resistivity are investigated and explained in detail. From the presented results, the fundamental understanding needed for optimizing the poly-Si-based carrier selective junction in respect to the main design parameters such as doping level in poly-Si, annealing time, silicon oxide thickness, and pinhole density is given. The detailed analysis shows the pinhole channel plays the most crucial role in the design of poly-Si-based carrier-selective junctions if the silicon oxide layer thickness is larger than 2 nm.
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S. Bordihn, B. Min, R. Peibst, and R. Brendel Modelling of Passivation and Resistance of n-Type poly-Si Layers by Trained Artificial Neural Networks Inproceedings WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 176-179, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: Artificial Neural Network, Modelling / Modeling, Polycrystalline Silicon (Si), surface passivation @inproceedings{Bordihn2019b,
title = {Modelling of Passivation and Resistance of n-Type poly-Si Layers by Trained Artificial Neural Networks}, author = {S Bordihn and B Min and R Peibst and R Brendel}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-2BO.3.1}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {176-179}, address = {Marseille, France}, abstract = {This paper studies the passivation quality and sheet resistance of n-type poly-Si on oxide (POLO) layers that we prepare at various post-deposition annealing temperatures. The n-type poly-Si layers are 50 nm-thin and grown on textured and planar Cz Si substrates. The samples are annealed from 880 °C to 1000 °C to transform the amorphous Si to poly-crystalline Si. The surface passivation quality is evaluated after the aforementioned anneal step, after an additional hydrogenation step (induced by Al2O3 capping layers and subsequent low temperature anneal), and after firing at 840 °C peak temperature. The optimal surface passivation quality is found for annealing at 960 °C and hydrogenation, resulting in iVoc-values of 710 mV. The hydrogenation step improves the iVoc by ~20 mV depending on the post-deposition annealing temperature. We find that surface passivation and sheet resistance of the poly-Si layers increased with increasing anneal temperature up to 960 °C and starts to decline above 980 °C. This trend is found to correlate with the amount of in-diffused dopants that depends also on the annealing temperature. We show that artificial neural network based model can serve as a fast tool for predicting layer properties that depend on multiple process parameters. The quality of the modelling is the same as that using the Design of Experiment method. }, keywords = {Artificial Neural Network, Modelling / Modeling, Polycrystalline Silicon (Si), surface passivation}, pubstate = {published}, tppubtype = {inproceedings} } This paper studies the passivation quality and sheet resistance of n-type poly-Si on oxide (POLO) layers that we prepare at various post-deposition annealing temperatures. The n-type poly-Si layers are 50 nm-thin and grown on textured and planar Cz Si substrates. The samples are annealed from 880 °C to 1000 °C to transform the amorphous Si to poly-crystalline Si. The surface passivation quality is evaluated after the aforementioned anneal step, after an additional hydrogenation step (induced by Al2O3 capping layers and subsequent low temperature anneal), and after firing at 840 °C peak temperature. The optimal surface passivation quality is found for annealing at 960 °C and hydrogenation, resulting in iVoc-values of 710 mV. The hydrogenation step improves the iVoc by ~20 mV depending on the post-deposition annealing temperature. We find that surface passivation and sheet resistance of the poly-Si layers increased with increasing anneal temperature up to 960 °C and starts to decline above 980 °C. This trend is found to correlate with the amount of in-diffused dopants that depends also on the annealing temperature. We show that artificial neural network based model can serve as a fast tool for predicting layer properties that depend on multiple process parameters. The quality of the modelling is the same as that using the Design of Experiment method.
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M. R. Vogt, R. Witteck, T. Gewohn, H. Schulte-Huxel, C. Schinke, M. Köntges, K. Bothe, and R. Brendel WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 795-800, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: Antireflection Coating, module integration, Optical losses, PV Module, ray tracing, Simulation @inproceedings{Vogt2019c,
title = {Boosting PV Module Efficiency Beyond the Efficiency of Its Solar Cells – A Raytracing Study with Daidalos Now Available to the Scientific Community}, author = {M R Vogt and R Witteck and T Gewohn and H Schulte-Huxel and C Schinke and M Köntges and K Bothe and R Brendel}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-4BO.11.3}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {795-800}, address = {Marseille, France}, abstract = {Today, the PV module energy conversion efficiency is below the efficiency of the cells prior to module integration. Using optical ray tracing simulations, we show how to increase module efficiencies beyond the efficiency of the solar cells. To achieve this we follow two basic principles: First, we minimize optical losses of the module components by minimizing the absorption in the glass and the encapsulation as well as by introducing multilayer glass ARC coatings that reduce the surface reflection. Second, we exploit the internal reflection at the glass-air interface by using light guiding structures in the cell gaps and as cell connects. This improves the light trapping by reducing the cell front side reflection losses. In our specific example presented in this work, the optimization leads to a module efficiency of 20.9%, which is a 0.1%abs above that of the non-encapsulated cells with an efficiency of 20.8%. }, keywords = {Antireflection Coating, module integration, Optical losses, PV Module, ray tracing, Simulation}, pubstate = {published}, tppubtype = {inproceedings} } Today, the PV module energy conversion efficiency is below the efficiency of the cells prior to module integration. Using optical ray tracing simulations, we show how to increase module efficiencies beyond the efficiency of the solar cells. To achieve this we follow two basic principles: First, we minimize optical losses of the module components by minimizing the absorption in the glass and the encapsulation as well as by introducing multilayer glass ARC coatings that reduce the surface reflection. Second, we exploit the internal reflection at the glass-air interface by using light guiding structures in the cell gaps and as cell connects. This improves the light trapping by reducing the cell front side reflection losses. In our specific example presented in this work, the optimization leads to a module efficiency of 20.9%, which is a 0.1%abs above that of the non-encapsulated cells with an efficiency of 20.8%.
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Y. Larionova, H. Schulte-Huxel, B. Min, S. Hartmann, M. Turcu, T. Kluge, H. Mehlich, R. Brendel, and R. Peibst Screen Printed Double-Side Contacted POLO-Cells with Ultra-Thin Poly-Si Layers and Different Transparent Conductive Oxides Inproceedings WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 172-175, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: passivating contact, Polycrystalline Silicon (Si), silicon solar cells, Transparent Conducting Oxides (TCO) @inproceedings{Larionova2019b,
title = {Screen Printed Double-Side Contacted POLO-Cells with Ultra-Thin Poly-Si Layers and Different Transparent Conductive Oxides}, author = {Y Larionova and H Schulte-Huxel and B Min and S Hartmann and M Turcu and T Kluge and H Mehlich and R Brendel and R Peibst}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-2BO.2.6}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {172-175}, address = {Marseille, France}, abstract = {In this work we demonstrate various measures to improve the efficiency of large-area screen-printed double-side contacted POLO-cells with different transparent conductive oxides (TCO). We experimentally increase the short-circuit current density Jsc up to 0.6 mA/cm2 by reducing the thickness of poly-Si from 25 nm to 10 nm due to the reduction of the parasitic absorption in the poly-Si layer at the textured cell front side. An implemented hydrogenation step with AlxOy and post-deposition anneal of TCO enable remarkably high implied open-circuit voltage Voc,impl values on n-type cell precursors after the sputtering process. All cell precursors show Voc,impl of up to 740 mV independent of the poly-Si thickness. We find an improvement of the open-circuit voltage Voc of the final cells of up to 728 mV, a cell efficiency of up to 22.3% with indium tin oxide, and a cell efficiency of 21.6% with an aluminum-doped zinc oxide on top or the n+-type POLO layer. }, keywords = {passivating contact, Polycrystalline Silicon (Si), silicon solar cells, Transparent Conducting Oxides (TCO)}, pubstate = {published}, tppubtype = {inproceedings} } In this work we demonstrate various measures to improve the efficiency of large-area screen-printed double-side contacted POLO-cells with different transparent conductive oxides (TCO). We experimentally increase the short-circuit current density Jsc up to 0.6 mA/cm2 by reducing the thickness of poly-Si from 25 nm to 10 nm due to the reduction of the parasitic absorption in the poly-Si layer at the textured cell front side. An implemented hydrogenation step with AlxOy and post-deposition anneal of TCO enable remarkably high implied open-circuit voltage Voc,impl values on n-type cell precursors after the sputtering process. All cell precursors show Voc,impl of up to 740 mV independent of the poly-Si thickness. We find an improvement of the open-circuit voltage Voc of the final cells of up to 728 mV, a cell efficiency of up to 22.3% with indium tin oxide, and a cell efficiency of 21.6% with an aluminum-doped zinc oxide on top or the n+-type POLO layer.
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A. Lachowicz, G. Christmann, A. Descoeudres, B. Min, S. Bordihn, R. Peibst, S. Nicolay, and C. Ballif Metallization Grid on Azo by Electrodeposition of Copper Inproceedings WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 677-678, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: Aluminum Zin Oxide, CIGS, Copper Plating, Solar Cells @inproceedings{Lachowicz2019,
title = {Metallization Grid on Azo by Electrodeposition of Copper}, author = {A Lachowicz and G Christmann and A Descoeudres and B Min and S Bordihn and R Peibst and S Nicolay and C Ballif}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-3BV.1.28}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {677-678}, address = {Marseille, France}, abstract = {Aluminum zinc oxide is chemically very sensitive and wet processing solutions have to be carefully chosen. We present a process sequence for electrodeposition of copper on solar cells, originally developed for heterojunction cells with indium thin oxide and modified for solar cells with aluminum zinc oxide. The process comprises a sputtered seed layer and patterning by hotmelt inkjet printing. High efficiency above 24.7% and excellent reliability have been demonstrated on heterojunction cells with ITO, good fill factor achieved on c-Si cells with poly-Si carrier selective contacts with AZO and the process has been demonstrated on industrial CIGS substrates. }, keywords = {Aluminum Zin Oxide, CIGS, Copper Plating, Solar Cells}, pubstate = {published}, tppubtype = {inproceedings} } Aluminum zinc oxide is chemically very sensitive and wet processing solutions have to be carefully chosen. We present a process sequence for electrodeposition of copper on solar cells, originally developed for heterojunction cells with indium thin oxide and modified for solar cells with aluminum zinc oxide. The process comprises a sputtered seed layer and patterning by hotmelt inkjet printing. High efficiency above 24.7% and excellent reliability have been demonstrated on heterojunction cells with ITO, good fill factor achieved on c-Si cells with poly-Si carrier selective contacts with AZO and the process has been demonstrated on industrial CIGS substrates.
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D. C. Walter, L. Helmich, T. Pernau, O. Romer, and J. Schmidt Comparing Cz-Si PERC Solar Cells from Various Manufacturers Regarding BO-Related Light-Induced Degradation and Regeneration Inproceedings WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 464-467, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: Czochralski (Cz), LID, solar cell @inproceedings{Walter2019cb,
title = {Comparing Cz-Si PERC Solar Cells from Various Manufacturers Regarding BO-Related Light-Induced Degradation and Regeneration}, author = {D C Walter and L Helmich and T Pernau and O Romer and J Schmidt}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-2CV.2.101}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {464-467}, address = {Marseille, France}, abstract = {Within this study, we investigate the impact of boron-oxygen (BO)-related defect centers on the performance of passivated emitter and rear solar cells (PERCs), made of boron-doped Czochralski-grown silicon, taken from mass production lines of seven different manufacturers. Before light-induced degradation (LID), the efficiencies of the PERC cells vary between 18.5% and 20.4%. In all cases, the conversion efficiency decreases upon illumination, however, the degradation extent varies considerably between the different manufacturers ranging from 0.3 to 1.6%abs. A lab-type regeneration treatment at 185°C and 1.5 suns halogen-lamp light intensity is able to reach the same efficiency values as before LID after complete regeneration for all but one cell group, considering the measurement uncertainties. Importantly, our measurements show that after full regeneration the open-circuit voltage of the cells is stable upon prolonged illumination at room temperature, independent of the applied regeneration treatment, which we performed either under lab conditions or in the c.REG regeneration furnace from centrotherm. This underlines the successful deactivation of the BO defect. Finally, on PERC cells of a single manufacturer, we study the dependence of regeneration rate constant Rde on the applied illumination intensity during regeneration. We observe that at high intensities, the regeneration rate constant seems to saturate. Hence, we conclude that very high light intensities (above ~5 suns) are not necessary or beneficial to achieve a fast regeneration. }, keywords = {Czochralski (Cz), LID, solar cell}, pubstate = {published}, tppubtype = {inproceedings} } Within this study, we investigate the impact of boron-oxygen (BO)-related defect centers on the performance of passivated emitter and rear solar cells (PERCs), made of boron-doped Czochralski-grown silicon, taken from mass production lines of seven different manufacturers. Before light-induced degradation (LID), the efficiencies of the PERC cells vary between 18.5% and 20.4%. In all cases, the conversion efficiency decreases upon illumination, however, the degradation extent varies considerably between the different manufacturers ranging from 0.3 to 1.6%abs. A lab-type regeneration treatment at 185°C and 1.5 suns halogen-lamp light intensity is able to reach the same efficiency values as before LID after complete regeneration for all but one cell group, considering the measurement uncertainties. Importantly, our measurements show that after full regeneration the open-circuit voltage of the cells is stable upon prolonged illumination at room temperature, independent of the applied regeneration treatment, which we performed either under lab conditions or in the c.REG regeneration furnace from centrotherm. This underlines the successful deactivation of the BO defect. Finally, on PERC cells of a single manufacturer, we study the dependence of regeneration rate constant Rde on the applied illumination intensity during regeneration. We observe that at high intensities, the regeneration rate constant seems to saturate. Hence, we conclude that very high light intensities (above ~5 suns) are not necessary or beneficial to achieve a fast regeneration.
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M-U. Halbich, R. Sauer-Stieglitz, W. Lövenich, and J. Schmidt Improving Organic-Silicon Heterojunction Solar Cells through the Admixture of Sorbitol to PEDOT:PSS Inproceedings WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 214-218, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: PEDOT:PSS @inproceedings{Halbich2019c,
title = {Improving Organic-Silicon Heterojunction Solar Cells through the Admixture of Sorbitol to PEDOT:PSS}, author = {M-U Halbich and R Sauer-Stieglitz and W Lövenich and J Schmidt}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-2CO.9.6}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {214-218}, address = {Marseille, France}, abstract = {We examine the impact of Sorbitol admixture on the hole conductive polymer PEDOT:PSS[poly(3,4ethylenedioxythiophene):poly(styrenesulfonate)] in combination with a variation of the annealing duration. As demonstrated in a previous publication, the admixture of Sorbitol to the PEDOT:PSS dispersion is improving the transparency of the organic layer and is also improving the surface passivation. On the other hand, the contact resistance on the silicon surface tends to increase by admixture of Sorbitol. In this study, we fabricate solar cells where the PEDOT:PSS layer is used as a hole-selective contact at the cell rear (so-called ‘BackPEDOT’ solar cells). The electron-selective front is conventionally processed by means of phosphorus diffusion. The passivation of the silicon surface with PEDOT:PSS:Sorbitol shows an improvement in the passivation quality and the solar cells show an increasing open-circuit voltage Voc by increasing the annealing duration from the previously routinely applied 10 min to 60 min. The short-circuit current density Jsc of the fabricated solar cells remains unchanged for all investigated annealing durations. Importantly, the series resistance Rs (and hence the contact resistance) of the fabricated BackPEDOT solar cells show a minimum for annealing durations between 45 and 90 min. As a consequence, increasing the annealing duration led to an increased maximum energy conversion efficiency of 20.6% at one sun.}, keywords = {PEDOT:PSS}, pubstate = {published}, tppubtype = {inproceedings} } We examine the impact of Sorbitol admixture on the hole conductive polymer PEDOT:PSS[poly(3,4ethylenedioxythiophene):poly(styrenesulfonate)] in combination with a variation of the annealing duration. As demonstrated in a previous publication, the admixture of Sorbitol to the PEDOT:PSS dispersion is improving the transparency of the organic layer and is also improving the surface passivation. On the other hand, the contact resistance on the silicon surface tends to increase by admixture of Sorbitol. In this study, we fabricate solar cells where the PEDOT:PSS layer is used as a hole-selective contact at the cell rear (so-called ‘BackPEDOT’ solar cells). The electron-selective front is conventionally processed by means of phosphorus diffusion. The passivation of the silicon surface with PEDOT:PSS:Sorbitol shows an improvement in the passivation quality and the solar cells show an increasing open-circuit voltage Voc by increasing the annealing duration from the previously routinely applied 10 min to 60 min. The short-circuit current density Jsc of the fabricated solar cells remains unchanged for all investigated annealing durations. Importantly, the series resistance Rs (and hence the contact resistance) of the fabricated BackPEDOT solar cells show a minimum for annealing durations between 45 and 90 min. As a consequence, increasing the annealing duration led to an increased maximum energy conversion efficiency of 20.6% at one sun.
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D. Bredemeier, D. C. Walter, R. Heller, and J. Schmidt Impact of Silicon Nitride Film Properties on Hydrogen In-Diffusion into Crystalline Silicon Inproceedings WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 112-115, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: diffusion, Hydrogen, Rapid thermal annealing, silicon nitride @inproceedings{Bredemeier2019d,
title = {Impact of Silicon Nitride Film Properties on Hydrogen In-Diffusion into Crystalline Silicon}, author = {D Bredemeier and D C Walter and R Heller and J Schmidt}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-2AO.4.4}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {112-115}, address = {Marseille, France}, abstract = {Hydrogen-rich silicon nitride films deposited on top of crystalline silicon wafers are a common source of hydrogen within solar cell production. Upon rapid thermal annealing (RTA), hydrogen bonds within the silicon nitride films dissociate and the hydrogen diffuses both into the environment as well as into the silicon bulk. Within this study, we investigate the impact of silicon nitride material properties on the amount of hydrogen introduced into the silicon bulk during RTA treatment. The measurements clearly show that the atomic density of the silicon nitride film has a pronounced impact on the hydrogen in-diffusion. Importantly, we find that the total hydrogen loss during RTA within the silicon nitride films is not correlated with the actual amount of hydrogen introduced into the silicon bulk.}, keywords = {diffusion, Hydrogen, Rapid thermal annealing, silicon nitride}, pubstate = {published}, tppubtype = {inproceedings} } Hydrogen-rich silicon nitride films deposited on top of crystalline silicon wafers are a common source of hydrogen within solar cell production. Upon rapid thermal annealing (RTA), hydrogen bonds within the silicon nitride films dissociate and the hydrogen diffuses both into the environment as well as into the silicon bulk. Within this study, we investigate the impact of silicon nitride material properties on the amount of hydrogen introduced into the silicon bulk during RTA treatment. The measurements clearly show that the atomic density of the silicon nitride film has a pronounced impact on the hydrogen in-diffusion. Importantly, we find that the total hydrogen loss during RTA within the silicon nitride films is not correlated with the actual amount of hydrogen introduced into the silicon bulk.
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J. Ulbikas, V. Ulbikaite, J. Denafas, R. Witteck, M. Köntges, M. Topic, F. Frontini, P. Bonomo, E. Saretta, P. Macé, P. J. Bolt, A. G. Ulyashin, T. Haarberg, W. Palitzsch, B. Terheiden, I. Weiss, Fuentes. A. Cano, and J. L. Domínguez-García Super PV Project – Innovative and High-Quality PV Systems to Regain Leadership of European PV Businesses on the World Market Inproceedings WIP (Ed.): Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition, 1972-1976, Marseille, France, (2019), ISBN: 3-936338-60-4. Abstract | Links | BibTeX | Tags: Economic Analysis, LCA, LCOE, PV Markets, Solar PV @inproceedings{Ulbikas2019b,
title = {Super PV Project – Innovative and High-Quality PV Systems to Regain Leadership of European PV Businesses on the World Market}, author = {J Ulbikas and V Ulbikaite and J Denafas and R Witteck and M Köntges and M Topic and F Frontini and P Bonomo and E Saretta and P Macé and P J Bolt and A G Ulyashin and T Haarberg and W Palitzsch and B Terheiden and I Weiss and A Fuentes Cano and J L Domínguez-García}, editor = {WIP}, doi = {10.4229/EUPVSEC20192019-7DV.2.1}, isbn = {3-936338-60-4}, year = {2019}, date = {2019-10-23}, booktitle = {Proceedings of the 36th European Photovoltaic Solar Energy Conference and Exhibition}, pages = {1972-1976}, address = {Marseille, France}, abstract = {PV deployment growth is an unmatched success story in the energy sector over recent years. However, European PV manufacturers are facing a decline in production due to competition from third countries. The fragmentation of the value chain is believed to be one of the major factors for this decrease in the competitiveness. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. It pursues a significant LCOE reduction for innovative PV systems based on a hybrid combination of technological innovations and data management solutions along the PV value chain. Responding to the need of evaluating proposed innovations in terms of economic feasibility and market trends, a dedicated task force, an Exploitation Team, was introduced at the beginning of the project as a main instrument for overseeing achievement of KPI’s and beyond, in the ever-changing landscape of the PV sector. }, keywords = {Economic Analysis, LCA, LCOE, PV Markets, Solar PV}, pubstate = {published}, tppubtype = {inproceedings} } PV deployment growth is an unmatched success story in the energy sector over recent years. However, European PV manufacturers are facing a decline in production due to competition from third countries. The fragmentation of the value chain is believed to be one of the major factors for this decrease in the competitiveness. SUPER PV is a collaborative European-funded project initiated in 2018 by 26 partners in reaction to this trend. It pursues a significant LCOE reduction for innovative PV systems based on a hybrid combination of technological innovations and data management solutions along the PV value chain. Responding to the need of evaluating proposed innovations in terms of economic feasibility and market trends, a dedicated task force, an Exploitation Team, was introduced at the beginning of the project as a main instrument for overseeing achievement of KPI’s and beyond, in the ever-changing landscape of the PV sector.
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H. Wirth, M. Vehse, B. Rau, R. Peibst, A. Colsmann, A. Stephan, and P. Lechner Integrierte Photovoltaik Presentation/Poster Berlin, Germany, 23.10.2019, (FVEE-Jahrestagung 2019 "Energy Research for Future"). @misc{Wirth2019,
title = {Integrierte Photovoltaik}, author = {H Wirth and M Vehse and B Rau and R Peibst and A Colsmann and A Stephan and P Lechner}, year = {2019}, date = {2019-10-23}, address = {Berlin, Germany}, note = {FVEE-Jahrestagung 2019 "Energy Research for Future"}, keywords = {FVEE}, pubstate = {published}, tppubtype = {presentation} } |