Veröffentlichungen
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E. L. Warren, M. G. Deceglie, M. Rienacker, R. Peibst, A. C. Tamboli, and P. Stradins Maximizing tandem solar cell power extraction using a three-terminal design Artikel Sustainable Energy Fuels 2 (6), 1141-1147 (2018). Abstract | Links | BibTeX | Schlagwörter: Tandem @article{Warren2018,
title = {Maximizing tandem solar cell power extraction using a three-terminal design}, author = {E L Warren and M G Deceglie and M Rienacker and R Peibst and A C Tamboli and P Stradins}, doi = {10.1039/C8SE00133B}, year = {2018}, date = {2018-06-01}, journal = {Sustainable Energy Fuels}, volume = {2}, number = {6}, pages = {1141-1147}, publisher = {The Royal Society of Chemistry}, abstract = {Tandem or multijunction solar cells can greatly increase the efficiency of solar energy conversion by absorbing different energies of the incident solar illumination in semiconductors with different band-gaps, which can operate more efficiently than a single absorber. Many different designs of tandem cells based on high efficiency top cells and Si bottom cells have been proposed, and there is ongoing debate as to whether the sub-cells should be wired in series (to create a tandem device with two terminals) or operated independently (four terminals). An alternative cell configuration that combines some of the strengths of both is a three-terminal device consisting of a top cell optically in series with a modified interdigitated back contact (IBC) Si cell featuring a conductive top contact. Such a configuration can enable improved energy yield while only requiring external wiring on the front and back of the solar cell stack. In this paper, we investigate the operation of three terminal tandems in detail using technology computer aided design (TCAD) device physics simulations. Using III-V top cells as an example case, we show how the addition of a third terminal can deliver comparable power output to a four terminal device, and substantially more power than a two-terminal device, while also enabling power injection and extraction between the two sub-circuits under a variety of spectral conditions.}, keywords = {Tandem}, pubstate = {published}, tppubtype = {article} } Tandem or multijunction solar cells can greatly increase the efficiency of solar energy conversion by absorbing different energies of the incident solar illumination in semiconductors with different band-gaps, which can operate more efficiently than a single absorber. Many different designs of tandem cells based on high efficiency top cells and Si bottom cells have been proposed, and there is ongoing debate as to whether the sub-cells should be wired in series (to create a tandem device with two terminals) or operated independently (four terminals). An alternative cell configuration that combines some of the strengths of both is a three-terminal device consisting of a top cell optically in series with a modified interdigitated back contact (IBC) Si cell featuring a conductive top contact. Such a configuration can enable improved energy yield while only requiring external wiring on the front and back of the solar cell stack. In this paper, we investigate the operation of three terminal tandems in detail using technology computer aided design (TCAD) device physics simulations. Using III-V top cells as an example case, we show how the addition of a third terminal can deliver comparable power output to a four terminal device, and substantially more power than a two-terminal device, while also enabling power injection and extraction between the two sub-circuits under a variety of spectral conditions.
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F. Haase, B. Lim, A. Merkle, T. Dullweber, R. Brendel, C. Günther, M. H. Holthausen, C. Mader, O. Wunnicke, and R. Peibst Printable liquid silicon for local doping of solar cells Artikel Solar Energy Materials and Solar Cells 179 , 129-135 (2018), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: Back-contact solar cell, Local doping, Out diffused emitters, Printable silicon @article{Haase2017b,
title = {Printable liquid silicon for local doping of solar cells}, author = {F Haase and B Lim and A Merkle and T Dullweber and R Brendel and C Günther and M H Holthausen and C Mader and O Wunnicke and R Peibst}, doi = {10.1016/j.solmat.2017.11.003}, issn = {0927-0248}, year = {2018}, date = {2018-06-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {179}, pages = {129-135}, abstract = {We demonstrate the application of a liquid-processed doped silicon precursor as a doping source for the fabrication of interdigitated back contact solar cells. We integrate phosphorus- as well as boron-doped liquid silicon in our n-type interdigitated back contact cell process based on laser-structuring. The cell with the phosphorus back surface field from liquid silicon has an efficiency of 20.9% and the cell with the boron emitter from liquid silicon has an efficiency of 21.9%. We measure saturation current densities of 34fAcm−2 on phosphorus-doped layers with a sheet resistance of 108Ω/sq and 18fAcm−2 on boron-doped layers with a sheet resistance of 140Ω/sq using passivated test samples.}, keywords = {Back-contact solar cell, Local doping, Out diffused emitters, Printable silicon}, pubstate = {published}, tppubtype = {article} } We demonstrate the application of a liquid-processed doped silicon precursor as a doping source for the fabrication of interdigitated back contact solar cells. We integrate phosphorus- as well as boron-doped liquid silicon in our n-type interdigitated back contact cell process based on laser-structuring. The cell with the phosphorus back surface field from liquid silicon has an efficiency of 20.9% and the cell with the boron emitter from liquid silicon has an efficiency of 21.9%. We measure saturation current densities of 34fAcm−2 on phosphorus-doped layers with a sheet resistance of 108Ω/sq and 18fAcm−2 on boron-doped layers with a sheet resistance of 140Ω/sq using passivated test samples.
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R. Peibst, Y. Larionova, S. Reiter, T. F. Wietler, N. Orlowski, S. Schäfer, B. Min, M. Stratmann, D. Tetzlaff, J. Krügener, U. Höhne, J. D. Kähler, H. Mehlich, S. Frigge, and R. Brendel IEEE Journal of Photovoltaics 8 (3), 719-725 (2018), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Carrier Selective Contacts, passivation, Polycrystalline silicon, Silicon solar cell, transparent conductive oxide, Zinc oxide @article{Peibst2018,
title = {Building Blocks for Industrial, Screen-Printed Double-Side Contacted POLO Cells With Highly Transparent ZnO:Al Layers}, author = {R Peibst and Y Larionova and S Reiter and T F Wietler and N Orlowski and S Schäfer and B Min and M Stratmann and D Tetzlaff and J Krügener and U Höhne and J D Kähler and H Mehlich and S Frigge and R Brendel}, doi = {10.1109/JPHOTOV.2018.2813427}, issn = {2156-3381}, year = {2018}, date = {2018-05-01}, journal = {IEEE Journal of Photovoltaics}, volume = {8}, number = {3}, pages = {719-725}, abstract = {We report on an industrial large area, screen-printed, double-side contacted cell with polysilicon on oxide (POLO) junctions on both sides and an energy conversion efficiency of 22.3% (A = 244.15 cm 2, Voc = 714 mV, FF = 81.1%, Jsc = 38.5 mA/cm2, measured in-house). This cell shows an extraordinarily low series resistance below 0.05 Ω cm2. This confirms the low specific junction resistance observed recently for POLO junctions. The present cell suffers from 1) low short-circuit current due to parasitic absorption in the rather thick poly-Si (30 nm), as well as in the indium tin oxide, 2) deterioration of the recombination behavior upon sputter deposition of a transparent conductive oxide (TCO), and 3) shunts near the edge due to nonadapted TCO edge exclusion. We address all of these limitations experimentally. In particular, we developed a plasma-enhanced chemical vapor deposition process for ZnO:Al, which does not compromise the passivation of the POLO junctions underneath. An estimation of the efficiency potential (based on the two-diode model and the assumption that all these building blocks can be successfully combined on a cell level) shows that 25.3% can be achieved with this cell concept. We also look into potential cost advantages of the POLO junction scheme for this cell structure, such as the usage of p-type Cz-Si material and the omission of Ag fingers.}, keywords = {Carrier Selective Contacts, passivation, Polycrystalline silicon, Silicon solar cell, transparent conductive oxide, Zinc oxide}, pubstate = {published}, tppubtype = {article} } We report on an industrial large area, screen-printed, double-side contacted cell with polysilicon on oxide (POLO) junctions on both sides and an energy conversion efficiency of 22.3% (A = 244.15 cm 2, Voc = 714 mV, FF = 81.1%, Jsc = 38.5 mA/cm2, measured in-house). This cell shows an extraordinarily low series resistance below 0.05 Ω cm2. This confirms the low specific junction resistance observed recently for POLO junctions. The present cell suffers from 1) low short-circuit current due to parasitic absorption in the rather thick poly-Si (30 nm), as well as in the indium tin oxide, 2) deterioration of the recombination behavior upon sputter deposition of a transparent conductive oxide (TCO), and 3) shunts near the edge due to nonadapted TCO edge exclusion. We address all of these limitations experimentally. In particular, we developed a plasma-enhanced chemical vapor deposition process for ZnO:Al, which does not compromise the passivation of the POLO junctions underneath. An estimation of the efficiency potential (based on the two-diode model and the assumption that all these building blocks can be successfully combined on a cell level) shows that 25.3% can be achieved with this cell concept. We also look into potential cost advantages of the POLO junction scheme for this cell structure, such as the usage of p-type Cz-Si material and the omission of Ag fingers.
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C. N. Kruse, K. Bothe, and R. Brendel IEEE Journal of Photovoltaics 8 (3), 683-688 (2018), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Characterization, Metrology, performance loss, Photovoltaic cells, Si PV modeling @article{Kruse2018,
title = {Comparison of Free Energy Loss Analysis and Synergistic Efficiency Gain Analysis for PERC Solar Cells}, author = {C N Kruse and K Bothe and R Brendel}, doi = {10.1109/JPHOTOV.2018.2802779}, issn = {2156-3381}, year = {2018}, date = {2018-05-01}, journal = {IEEE Journal of Photovoltaics}, volume = {8}, number = {3}, pages = {683-688}, abstract = {The optimization of a solar cell requires a detailed knowledge of the efficiency limiting power losses. The free energy loss analysis (FELA) and the synergistic efficiency gain analysis (SEGA) both allow for studying these power losses. We compare both approaches for industrial passivated emitter and rear solar cells. The resistive losses calculated with both approaches are in good agreement with each other. In contrast, we find deviations of more than 20% for losses because of charge carrier recombination. From an analytical description of both methods, we conclude that these deviations are caused by a shift of the maximum power point voltage in an improved cell which is not considered in the FELA. The deviation of the losses critically depends on the specific loss channel investigated. In contrast with implied front-side power gains which are usually underestimated, rear-side or absorber gains can be over or underestimated by the FELA depending on the magnitude of the power loss. These differences follow from the Fermi level splitting which is affected differently by recombination currents at different locations. For an accurate determination of the efficiency improvement potential of individual recombination loss channels, we therefore recommend to perform a SEGA.}, keywords = {Characterization, Metrology, performance loss, Photovoltaic cells, Si PV modeling}, pubstate = {published}, tppubtype = {article} } The optimization of a solar cell requires a detailed knowledge of the efficiency limiting power losses. The free energy loss analysis (FELA) and the synergistic efficiency gain analysis (SEGA) both allow for studying these power losses. We compare both approaches for industrial passivated emitter and rear solar cells. The resistive losses calculated with both approaches are in good agreement with each other. In contrast, we find deviations of more than 20% for losses because of charge carrier recombination. From an analytical description of both methods, we conclude that these deviations are caused by a shift of the maximum power point voltage in an improved cell which is not considered in the FELA. The deviation of the losses critically depends on the specific loss channel investigated. In contrast with implied front-side power gains which are usually underestimated, rear-side or absorber gains can be over or underestimated by the FELA depending on the magnitude of the power loss. These differences follow from the Fermi level splitting which is affected differently by recombination currents at different locations. For an accurate determination of the efficiency improvement potential of individual recombination loss channels, we therefore recommend to perform a SEGA.
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S. Schäfer, and R. Brendel Accurate Calculation of the Absorptance Enhances Efficiency Limit of Crystalline Silicon Solar Cells With Lambertian Light Trapping Artikel Forthcoming IEEE Journal of Photovoltaics 1-3 Forthcoming, ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Efficiency limit, photon recycling, silicon, solar cell @article{Schäfer2018,
title = {Accurate Calculation of the Absorptance Enhances Efficiency Limit of Crystalline Silicon Solar Cells With Lambertian Light Trapping}, author = {S Schäfer and R Brendel}, doi = {10.1109/JPHOTOV.2018.2824024}, issn = {2156-3381}, year = {2018}, date = {2018-04-30}, journal = {IEEE Journal of Photovoltaics}, pages = {1-3}, abstract = {The widely accepted limiting efficiency for crystalline silicon solar cells with Lambertian light trapping under 1 sun was previously calculated to be 29.43% for a 110-μm-thick device by using the commonly applied weak absorption approximation for light trapping. However, the short-circuit current density increases by 0.17 mA/cm2 when modeling the optical absorptance of an ideal Lambertian light trapping scheme exactly. The resulting new 1-sun efficiency limit is 29.56% and holds for a cell that is 98.1 μm in thickness.}, keywords = {Efficiency limit, photon recycling, silicon, solar cell}, pubstate = {forthcoming}, tppubtype = {article} } The widely accepted limiting efficiency for crystalline silicon solar cells with Lambertian light trapping under 1 sun was previously calculated to be 29.43% for a 110-μm-thick device by using the commonly applied weak absorption approximation for light trapping. However, the short-circuit current density increases by 0.17 mA/cm2 when modeling the optical absorptance of an ideal Lambertian light trapping scheme exactly. The resulting new 1-sun efficiency limit is 29.56% and holds for a cell that is 98.1 μm in thickness.
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C. Gemmel, J. Hensen, L. David, S. Kajari-Schröder, and R. Brendel Kerfless epitaxial silicon wafers with 7 ms carrier lifetimes and a wide lift-off process window Artikel Japanese Journal of Applied Physics 57 (4), 041301 (2018). Abstract | Links | BibTeX | Schlagwörter: @article{Gemmel2018,
title = {Kerfless epitaxial silicon wafers with 7 ms carrier lifetimes and a wide lift-off process window}, author = {C Gemmel and J Hensen and L David and S Kajari-Schröder and R Brendel}, doi = {10.7567/JJAP.57.041301}, year = {2018}, date = {2018-04-01}, journal = {Japanese Journal of Applied Physics}, volume = {57}, number = {4}, pages = {041301}, abstract = {Silicon wafers contribute significantly to the photovoltaic module cost. Kerfless silicon wafers that grow epitaxially on porous silicon (PSI) and are subsequently detached from the growth substrate are a promising lower cost drop-in replacement for standard Czochralski (Cz) wafers. However, a wide technological processing window appears to be a challenge for this process. This holds in particularly for the etching current density of the separation layer that leads to lift-off failures if it is too large or too low. Here we present kerfless PSI wafers of high electronic quality that we fabricate on weakly reorganized porous Si with etch current densities varying in a wide process window from 110 to 150 mA/cm 2 . We are able to detach all 17 out of 17 epitaxial wafers. All wafers exhibit charge carrier lifetimes in the range of 1.9 to 4.3 ms at an injection level of 10^15 cm−3 without additional high-temperature treatment. We find even higher lifetimes in the range of 4.6 to 7.0 ms after applying phosphorous gettering. These results indicate that a weak reorganization of the porous layer can be beneficial for a large lift-off process window while still allowing for high carrier lifetimes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Silicon wafers contribute significantly to the photovoltaic module cost. Kerfless silicon wafers that grow epitaxially on porous silicon (PSI) and are subsequently detached from the growth substrate are a promising lower cost drop-in replacement for standard Czochralski (Cz) wafers. However, a wide technological processing window appears to be a challenge for this process. This holds in particularly for the etching current density of the separation layer that leads to lift-off failures if it is too large or too low. Here we present kerfless PSI wafers of high electronic quality that we fabricate on weakly reorganized porous Si with etch current densities varying in a wide process window from 110 to 150 mA/cm 2 . We are able to detach all 17 out of 17 epitaxial wafers. All wafers exhibit charge carrier lifetimes in the range of 1.9 to 4.3 ms at an injection level of 10^15 cm−3 without additional high-temperature treatment. We find even higher lifetimes in the range of 4.6 to 7.0 ms after applying phosphorous gettering. These results indicate that a weak reorganization of the porous layer can be beneficial for a large lift-off process window while still allowing for high carrier lifetimes.
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A. Pazidis, and R. Reineke-Koch Magnetron sputtered TiOx layers: Structural, electrical, optical and thermochromic aspects Artikel Thin Solid Films 649 , 43-50 (2018), ISSN: 0040-6090. Abstract | Links | BibTeX | Schlagwörter: Solar thermal collector, Thermochromic absorber, Titanium oxide @article{Pazidis2018b,
title = {Magnetron sputtered TiOx layers: Structural, electrical, optical and thermochromic aspects}, author = {A Pazidis and R Reineke-Koch}, doi = {10.1016/j.tsf.2017.12.019}, issn = {0040-6090}, year = {2018}, date = {2018-03-01}, journal = {Thin Solid Films}, volume = {649}, pages = {43-50}, abstract = {Titanium oxide layers were prepared by sputter deposition with plasma emission monitoring in the whole stoichiometry range between Ti and TiO2 without and with substrate heating to 240 °C. The layers were characterized with regard to their crystal structure and specific resistance. Optical constants were determined in the spectral range between 240 nm and 38 μm. The thermochromic behavior of a prepared Ti2O3 layer was measured and compared to calculations for bulk material.}, keywords = {Solar thermal collector, Thermochromic absorber, Titanium oxide}, pubstate = {published}, tppubtype = {article} } Titanium oxide layers were prepared by sputter deposition with plasma emission monitoring in the whole stoichiometry range between Ti and TiO2 without and with substrate heating to 240 °C. The layers were characterized with regard to their crystal structure and specific resistance. Optical constants were determined in the spectral range between 240 nm and 38 μm. The thermochromic behavior of a prepared Ti2O3 layer was measured and compared to calculations for bulk material.
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K. Bothe, D. Hinken, B. Min, and C. Schinke Accuracy of Simplifications for Spectral Responsivity Measurements of Solar Cells Artikel IEEE Journal of Photovoltaics 8 (2), 611-620 (2018), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: calibration, IEC 60904-8, solar cell, spectral mismatch, spectral responsivity @article{Bothe2018,
title = {Accuracy of Simplifications for Spectral Responsivity Measurements of Solar Cells}, author = {K Bothe and D Hinken and B Min and C Schinke}, doi = {10.1109/JPHOTOV.2018.2793758}, issn = {2156-3381}, year = {2018}, date = {2018-03-01}, journal = {IEEE Journal of Photovoltaics}, volume = {8}, number = {2}, pages = {611-620}, abstract = {The determination of the spectral responsivity is an essential part of solar cell characterization. Since solar simulators only approximate the reference spectrum, a spectral mismatch correction has to be performed. This correction procedure requires spectral responsivity data. Apart from the complete differential spectral responsivity procedure, the IEC 60904-8 standard defines four simplifications. In this paper, we provide information on the variations in the spectral responsivity curves for these simplifications. We show that for nonlinear front junction cells, deviations predominantly occur at wavelengths above 700 nm and become largest around 1000 nm. While we found a maximum deviation of 30% for the simplification with lowest requirements in bias irradiance, all other simplifications yield deviations below 10%. For a nonlinear cell measured relative to a world photovoltaic scale reference cell using a class A solar simulator, this transfers to a deviation below 0.01% in the spectral mismatch factor. If one depends on the use of a simplification, we recommend using the multicolor approach. Even though the singlecolor approach might yield lower deviations, this approach requires knowledge about the maximum in the spectral responsivity, which is not generally known in advance of the measurement. Accepting a slightly higher deviation, the white bias approach is a recommendable alternative.}, keywords = {calibration, IEC 60904-8, solar cell, spectral mismatch, spectral responsivity}, pubstate = {published}, tppubtype = {article} } The determination of the spectral responsivity is an essential part of solar cell characterization. Since solar simulators only approximate the reference spectrum, a spectral mismatch correction has to be performed. This correction procedure requires spectral responsivity data. Apart from the complete differential spectral responsivity procedure, the IEC 60904-8 standard defines four simplifications. In this paper, we provide information on the variations in the spectral responsivity curves for these simplifications. We show that for nonlinear front junction cells, deviations predominantly occur at wavelengths above 700 nm and become largest around 1000 nm. While we found a maximum deviation of 30% for the simplification with lowest requirements in bias irradiance, all other simplifications yield deviations below 10%. For a nonlinear cell measured relative to a world photovoltaic scale reference cell using a class A solar simulator, this transfers to a deviation below 0.01% in the spectral mismatch factor. If one depends on the use of a simplification, we recommend using the multicolor approach. Even though the singlecolor approach might yield lower deviations, this approach requires knowledge about the maximum in the spectral responsivity, which is not generally known in advance of the measurement. Accepting a slightly higher deviation, the white bias approach is a recommendable alternative.
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D. Zielke, R. Gogolin, M. -U. Halbich, C. Marquardt, W. Lövenich, R. Sauer, and J. Schmidt Large-Area PEDOT:PSS/c-Si Heterojunction Solar Cells With Screen-Printed Metal Contacts Artikel Solar RRL 2 (3), 1700191 (2018), ISSN: 2367-198X. Abstract | Links | BibTeX | Schlagwörter: large-areas, low-temperature pastes, PEDOT:PSS, screen-print, Solar Cells @article{Zielke2018,
title = {Large-Area PEDOT:PSS/c-Si Heterojunction Solar Cells With Screen-Printed Metal Contacts}, author = {D Zielke and R Gogolin and M -U Halbich and C Marquardt and W Lövenich and R Sauer and J Schmidt}, doi = {10.1002/solr.201700191}, issn = {2367-198X}, year = {2018}, date = {2018-03-01}, journal = {Solar RRL}, volume = {2}, number = {3}, pages = {1700191}, abstract = {A large‐area BackPEDOT solar cell with a phosphorus‐diffused emitter and a high‐temperature‐fired screen‐printed Ag grid on the front surface and PEDOT:PSS as hole‐collecting and passivating layer at the cell rear is developed. As base material, 15.6 × 15.6 cm2 pseudo‐square industrial‐type boron‐doped p‐type Czochralski‐grown silicon wafers are used. The set‐peak firing temperature (Tset) is varied from 850 to 870 °C with a total number of 32 processed solar cells. The optimum Tset of 870 °C results in a median solar cell efficiency of 19.0%. The best large‐area BackPEDOT solar cell achieves an efficiency of 20.2%. Based on external quantum efficiency measurements, a rear surface recombination velocity Srear < 70 cm s−1 is determined, a value which is on a par with today's industrial high‐efficiency solar cells. Furthermore, a low‐temperature metal paste is introduced, which is shown to be capable of metalizing the PEDOT:PSS‐covered rear surface of the solar cells without damaging the rear surface passivation. The principle feasibility of such a rear metallization scheme is demonstrated. The parasitic absorption of infrared light within the PEDOT:PSS layer is identified as the major loss mechanism in the current cells, which might be overcome in the future by adding infrared‐transparent additives to the PEDOT:PSS dispersion. }, keywords = {large-areas, low-temperature pastes, PEDOT:PSS, screen-print, Solar Cells}, pubstate = {published}, tppubtype = {article} } A large‐area BackPEDOT solar cell with a phosphorus‐diffused emitter and a high‐temperature‐fired screen‐printed Ag grid on the front surface and PEDOT:PSS as hole‐collecting and passivating layer at the cell rear is developed. As base material, 15.6 × 15.6 cm2 pseudo‐square industrial‐type boron‐doped p‐type Czochralski‐grown silicon wafers are used. The set‐peak firing temperature (Tset) is varied from 850 to 870 °C with a total number of 32 processed solar cells. The optimum Tset of 870 °C results in a median solar cell efficiency of 19.0%. The best large‐area BackPEDOT solar cell achieves an efficiency of 20.2%. Based on external quantum efficiency measurements, a rear surface recombination velocity Srear < 70 cm s−1 is determined, a value which is on a par with today's industrial high‐efficiency solar cells. Furthermore, a low‐temperature metal paste is introduced, which is shown to be capable of metalizing the PEDOT:PSS‐covered rear surface of the solar cells without damaging the rear surface passivation. The principle feasibility of such a rear metallization scheme is demonstrated. The parasitic absorption of infrared light within the PEDOT:PSS layer is identified as the major loss mechanism in the current cells, which might be overcome in the future by adding infrared‐transparent additives to the PEDOT:PSS dispersion.
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F. Haase, S. Schäfer, C. Klamt, F. Kiefer, J. Krügener, R. Brendel, and R. Peibst IEEE Journal of Photovoltaics 8 (1), 23-29 (2018), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Area measurement, charge carrier lifetime, Charge carrier lifetime analysis, Current measurement, Density measurement, Lighting, passivating contacts, perimeter recombination, Photovoltaic cells, Radiative recombination @article{Haase2018,
title = {Perimeter Recombination in 25%-Efficient IBC Solar Cells With Passivating POLO Contacts for Both Polarities}, author = {F Haase and S Schäfer and C Klamt and F Kiefer and J Krügener and R Brendel and R Peibst}, doi = {10.1109/JPHOTOV.2017.2762592}, issn = {2156-3381}, year = {2018}, date = {2018-01-01}, journal = {IEEE Journal of Photovoltaics}, volume = {8}, number = {1}, pages = {23-29}, abstract = {We introduce a method for the quantification of perimeter recombination in solar cells based on infrared lifetime measurements. We apply this method at a 25.0%-efficient interdigitated back contact (IBC) silicon solar cell with passivating contacts. The implied pseudo-efficiency determined by infrared lifetime mapping is 26.2% at an intermediate process step. The 1.2%abs loss is attributed to a process-related reduction in surface passivation quality, recombination in the perimeter area, and series resistance. The 2 × 2 cm2 -sized cell is processed on a 100 mm wafer. We determine the implied pseudo-efficiency with illuminated and with shaded perimeter area during infrared lifetime mapping. The difference between both implied pseudo-efficiencies yields the efficiency loss by perimeter recombination, which is determined to be 0.4%abs for a wafer resistivity of 1.3 Ω cm and even 0.9%abs for a wafer resistivity of 80 Ω cm.}, keywords = {Area measurement, charge carrier lifetime, Charge carrier lifetime analysis, Current measurement, Density measurement, Lighting, passivating contacts, perimeter recombination, Photovoltaic cells, Radiative recombination}, pubstate = {published}, tppubtype = {article} } We introduce a method for the quantification of perimeter recombination in solar cells based on infrared lifetime measurements. We apply this method at a 25.0%-efficient interdigitated back contact (IBC) silicon solar cell with passivating contacts. The implied pseudo-efficiency determined by infrared lifetime mapping is 26.2% at an intermediate process step. The 1.2%abs loss is attributed to a process-related reduction in surface passivation quality, recombination in the perimeter area, and series resistance. The 2 × 2 cm2 -sized cell is processed on a 100 mm wafer. We determine the implied pseudo-efficiency with illuminated and with shaded perimeter area during infrared lifetime mapping. The difference between both implied pseudo-efficiencies yields the efficiency loss by perimeter recombination, which is determined to be 0.4%abs for a wafer resistivity of 1.3 Ω cm and even 0.9%abs for a wafer resistivity of 80 Ω cm.
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D. Bredemeier, D. C. Walter, and J. Schmidt Solar RRL 2 (1), 1700159 (2018), ISSN: 2367-198X. Abstract | Links | BibTeX | Schlagwörter: Carrier lifetime, Degradation, diffusion, Multicrystalline silicon @article{Bredemeier2018,
title = {Possible Candidates for Impurities in mc-Si Wafers Responsible for Light-Induced Lifetime Degradation and Regeneration}, author = {D Bredemeier and D C Walter and J Schmidt}, doi = {10.1002/solr.201700159}, issn = {2367-198X}, year = {2018}, date = {2018-01-01}, journal = {Solar RRL}, volume = {2}, number = {1}, pages = {1700159}, abstract = {We examine the light‐induced carrier lifetime degradation and regeneration at elevated temperature in multicrystalline silicon (mc‐Si) wafers of different thicknesses. The experimental results show that the thinner the wafer the less pronounced the degradation is and the faster the regeneration takes place. We interpret this result in the framework of a recently proposed defect model, where the lifetime regeneration is attributed to the diffusion of the recombination‐active impurity to the wafer surfaces, where it is permanently trapped. Modeling the measured thickness‐dependent lifetime evolutions enables us to determine the diffusion coefficient of the impurity to be in the range (5 ± 2) × 10−11 cm2 s−1 at a temperature of 75 °C. Comparing the diffusion coefficient extracted from our measurements with data published in the literature allows us to exclude most impurities. Despite the large uncertainties in the diffusion coefficient data reported in the literature, reasonable agreement is only obtained for nickel, cobalt, and hydrogen. One important practical implication of our study is that mc‐Si wafers thinner than 120 μm do not suffer from pronounced light‐induced lifetime degradation. }, keywords = {Carrier lifetime, Degradation, diffusion, Multicrystalline silicon}, pubstate = {published}, tppubtype = {article} } We examine the light‐induced carrier lifetime degradation and regeneration at elevated temperature in multicrystalline silicon (mc‐Si) wafers of different thicknesses. The experimental results show that the thinner the wafer the less pronounced the degradation is and the faster the regeneration takes place. We interpret this result in the framework of a recently proposed defect model, where the lifetime regeneration is attributed to the diffusion of the recombination‐active impurity to the wafer surfaces, where it is permanently trapped. Modeling the measured thickness‐dependent lifetime evolutions enables us to determine the diffusion coefficient of the impurity to be in the range (5 ± 2) × 10−11 cm2 s−1 at a temperature of 75 °C. Comparing the diffusion coefficient extracted from our measurements with data published in the literature allows us to exclude most impurities. Despite the large uncertainties in the diffusion coefficient data reported in the literature, reasonable agreement is only obtained for nickel, cobalt, and hydrogen. One important practical implication of our study is that mc‐Si wafers thinner than 120 μm do not suffer from pronounced light‐induced lifetime degradation.
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B. Veith-Wolf, R. Witteck, A. Morlier, H. Schulte-Huxel, M. R. Vogt, and J. Schmidt Spectra-Dependent Stability of the Passivation Quality of Al2O3/c-Si Interfaces Artikel IEEE Journal of Photovoltaics 8 (1), 96-102 (2018), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Accelerated testing, Al2O3, Aluminum oxide, Carrier lifetime, crystalline silicon, Degradation, Long-term stability, silicon nitride (SiNx), surface passivation, ultraviolet (UV) stability @article{Veith-Wolf2018,
title = {Spectra-Dependent Stability of the Passivation Quality of Al2O3/c-Si Interfaces}, author = {B Veith-Wolf and R Witteck and A Morlier and H Schulte-Huxel and M R Vogt and J Schmidt}, doi = {10.1109/JPHOTOV.2017.2775147}, issn = {2156-3381}, year = {2018}, date = {2018-01-01}, journal = {IEEE Journal of Photovoltaics}, volume = {8}, number = {1}, pages = {96-102}, abstract = {We examine the stability of the c-Si surface passivation quality by spatial atomic-layer-deposited aluminum oxide (Al2O3), plasma-enhanced chemical vapor deposited silicon nitride (SiNx), and Al2O3/SiNx stacks under illumination with two different spectra. The Al2O3-passivated c-Si surfaces annealed at 350 °C show a weak degradation due to UV illumination, with surface recombination velocities (SRVs) of 122 cm/s after receiving a ultraviolet (UV) dose of 275 kWh/m2. Silicon samples passivated with Al2O3 layers that received a fast-firing step show an improvement due to UV illumination with a reduction of the SRVs initially from 14 to 5 cm/s for single Al2O3 layers. For the fired Al2O3 layers the negative fixed charge density increases from -6×1012 cm-2 up to -1.2×1013 cm-2 during UV illumination. We demonstrate that for the SiNx and the fired Al2O3 single layers, photons with energy greater than 3.4 eV are necessary to reduce the passivation quality. In contrast, low-temperature-annealed Al2O3 single layers and nonfired Al2O3/SiNx stacks showed a degradation already under illumination with a halogen lamp. Importantly, we observe a perfectly stable passivation on boron-diffused p+ emitter for fired Al2O3/SiNx stacks featuring a stable saturation current density of 18 fA/cm2 for a p+ sheet resistance of 90 Ω/sq.}, keywords = {Accelerated testing, Al2O3, Aluminum oxide, Carrier lifetime, crystalline silicon, Degradation, Long-term stability, silicon nitride (SiNx), surface passivation, ultraviolet (UV) stability}, pubstate = {published}, tppubtype = {article} } We examine the stability of the c-Si surface passivation quality by spatial atomic-layer-deposited aluminum oxide (Al2O3), plasma-enhanced chemical vapor deposited silicon nitride (SiNx), and Al2O3/SiNx stacks under illumination with two different spectra. The Al2O3-passivated c-Si surfaces annealed at 350 °C show a weak degradation due to UV illumination, with surface recombination velocities (SRVs) of 122 cm/s after receiving a ultraviolet (UV) dose of 275 kWh/m2. Silicon samples passivated with Al2O3 layers that received a fast-firing step show an improvement due to UV illumination with a reduction of the SRVs initially from 14 to 5 cm/s for single Al2O3 layers. For the fired Al2O3 layers the negative fixed charge density increases from -6×1012 cm-2 up to -1.2×1013 cm-2 during UV illumination. We demonstrate that for the SiNx and the fired Al2O3 single layers, photons with energy greater than 3.4 eV are necessary to reduce the passivation quality. In contrast, low-temperature-annealed Al2O3 single layers and nonfired Al2O3/SiNx stacks showed a degradation already under illumination with a halogen lamp. Importantly, we observe a perfectly stable passivation on boron-diffused p+ emitter for fired Al2O3/SiNx stacks featuring a stable saturation current density of 18 fA/cm2 for a p+ sheet resistance of 90 Ω/sq.
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D. C. Walter, R. Falster, V. V. Voronkov, and J. Schmidt On the equilibrium concentration of boron-oxygen defects in crystalline silicon Artikel Solar Energy Materials and Solar Cells 173 , 33-36 (2017), ISBN: 0927-0248, (Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics). Abstract | Links | BibTeX | Schlagwörter: boron-oxygen, Carrier lifetime, Czochralski silicon @article{Walter2017b,
title = {On the equilibrium concentration of boron-oxygen defects in crystalline silicon}, author = {D C Walter and R Falster and V V Voronkov and J Schmidt}, doi = {10.1016/j.solmat.2017.06.036}, isbn = {0927-0248}, year = {2017}, date = {2017-12-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {173}, pages = {33-36}, abstract = {We determine the equilibrium concentration of the BO defect in boron-doped Czochralski-grown silicon after prolonged (up to 150 h) annealing at relatively low temperatures between 200 and 300 °C. We show that after sample processing, the BO concentration has not necessarily reached the equilibrium state. The actually reached state depends on the detailed temperature profile of the last temperature treatment before the light-induced degradation (LID) is performed. For the investigated Cz-Si materials with base resistivities ranging between 0.5 and 2.5 Ω cm, we observe that an annealing step at 200 °C for 50 h establishes the equilibrium, independent of the base resistivity. Experiments performed at different temperatures reveal that the equilibrium defect concentration decreases with increasing annealing temperature. This observation can be understood, assuming a mobile species which is distributed between at least two different sinks. A possible defect model is discussed.}, note = {Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics}, keywords = {boron-oxygen, Carrier lifetime, Czochralski silicon}, pubstate = {published}, tppubtype = {article} } We determine the equilibrium concentration of the BO defect in boron-doped Czochralski-grown silicon after prolonged (up to 150 h) annealing at relatively low temperatures between 200 and 300 °C. We show that after sample processing, the BO concentration has not necessarily reached the equilibrium state. The actually reached state depends on the detailed temperature profile of the last temperature treatment before the light-induced degradation (LID) is performed. For the investigated Cz-Si materials with base resistivities ranging between 0.5 and 2.5 Ω cm, we observe that an annealing step at 200 °C for 50 h establishes the equilibrium, independent of the base resistivity. Experiments performed at different temperatures reveal that the equilibrium defect concentration decreases with increasing annealing temperature. This observation can be understood, assuming a mobile species which is distributed between at least two different sinks. A possible defect model is discussed.
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J. Krügener, F. Haase, M. Rienäcker, R. Brendel, H. J. Osten, and R. Peibst Solar Energy Materials and Solar Cells 173 , 85-91 (2017), ISSN: 0927-0248, (Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics). Abstract | Links | BibTeX | Schlagwörter: Carrier lifetime, Gettering, passivating contact, POLO, polysilicon, Silicon solar cell, solar cell @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 = {Carrier lifetime, Gettering, passivating contact, POLO, polysilicon, Silicon solar cell, solar cell}, 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%.
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D. Tetzlaff, J. Krügener, Y. Larionova, S. Reiter, M. Turcu, F. Haase, R. Brendel, R. Peibst, U. Höhne, J. -D. Kähler, and T. F. Wietler Solar Energy Materials and Solar Cells 173 , 106-110 (2017), ISSN: 0927-0248, (Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics). Abstract | Links | BibTeX | Schlagwörter: Carrier Selective Contacts, pinholes, polysilicon, Tetramethylammonium hydroxide (TMAH) @article{Tetzlaff2017c,
title = {A simple method for pinhole detection in carrier selective POLO-junctions for high efficiency silicon solar cells}, author = {D Tetzlaff and J Krügener and Y Larionova and S Reiter and M Turcu and F Haase and R Brendel and R Peibst and U Höhne and J -D Kähler and T F Wietler}, doi = {10.1016/j.solmat.2017.05.041}, issn = {0927-0248}, year = {2017}, date = {2017-12-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {173}, pages = {106-110}, abstract = {Polycrystalline silicon (poly-Si) layers on thin silicon oxide films have received strong research interest as they form excellent carrier selective junctions on crystalline silicon substrates after appropriate thermal processing. Recently, we presented a new method to determine the pinhole density in interfacial oxide films of poly-Si on oxide (POLO)-junctions with excellent electrical properties. The concept of magnification of nanometer-size pinholes in the interfacial oxide by selective etching of the underlying crystalline silicon is used to investigate the influence of annealing temperature on pinhole densities. Eventually, the pinholes are detected by optical microscopy and scanning electron microscopy. We present results on the pinhole density in POLO-junctions with J0 values as low as 1.4 fA/cm2. The stability of this method is demonstrated by proving that no new holes are introduced to the oxide during the etching procedure for a wide range of etching times. Finally, we show the applicability to multiple oxide types and thickness values, differently doped poly-Si layers as well as several types of wafer surface morphologies. For wet chemically grown oxides, we verified the existence of pinholes with an areal density of 2×10^7 cm−2 even already after annealing at a temperature of 750 °C (lower than the optimum annealing temperature for these junctions).}, note = {Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics}, keywords = {Carrier Selective Contacts, pinholes, polysilicon, Tetramethylammonium hydroxide (TMAH)}, pubstate = {published}, tppubtype = {article} } Polycrystalline silicon (poly-Si) layers on thin silicon oxide films have received strong research interest as they form excellent carrier selective junctions on crystalline silicon substrates after appropriate thermal processing. Recently, we presented a new method to determine the pinhole density in interfacial oxide films of poly-Si on oxide (POLO)-junctions with excellent electrical properties. The concept of magnification of nanometer-size pinholes in the interfacial oxide by selective etching of the underlying crystalline silicon is used to investigate the influence of annealing temperature on pinhole densities. Eventually, the pinholes are detected by optical microscopy and scanning electron microscopy. We present results on the pinhole density in POLO-junctions with J0 values as low as 1.4 fA/cm2. The stability of this method is demonstrated by proving that no new holes are introduced to the oxide during the etching procedure for a wide range of etching times. Finally, we show the applicability to multiple oxide types and thickness values, differently doped poly-Si layers as well as several types of wafer surface morphologies. For wet chemically grown oxides, we verified the existence of pinholes with an areal density of 2×10^7 cm−2 even already after annealing at a temperature of 750 °C (lower than the optimum annealing temperature for these junctions).
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D. Bredemeier, D. Walter, and J. Schmidt Solar Energy Materials and Solar Cells 173 , 2-5 (2017), ISSN: 0927-0248, (Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics). Abstract | Links | BibTeX | Schlagwörter: Carrier lifetime, Degradation, Multicrystalline silicon @article{Bredemeier2017b,
title = {Light-induced lifetime degradation in high-performance multicrystalline silicon: Detailed kinetics of the defect activation}, author = {D Bredemeier and D Walter and J Schmidt}, doi = {10.1016/j.solmat.2017.08.007}, issn = {0927-0248}, year = {2017}, date = {2017-12-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {173}, pages = {2-5}, abstract = {We examine the defect activation kinetics in block-cast high-performance multicrystalline silicon (HP mc-Si) under illumination at elevated temperature. Our lifetime analysis shows that the observed light-induced lifetime degradation consists of two separate stages: a fast stage followed by a slow stage. Our experiments reveal that both degradation stages can be fitted using a sum of two exponential decay functions. The resulting degradation rate constants depend both on the temperature and the light intensity applied during degradation. For the fast component, we determine an activation energy of (0.89 ± 0.04) eV from an Arrhenius plot of the degradation rate and for the slow component we determine a value of (0.94 ± 0.06) eV. The activation energies are relatively large, leading to a very pronounced dependence of the degradation rates on temperature. We also observe that both degradation rates show a linear dependence on the applied light intensity during degradation in the examined intensity range between 0.25 and 1.5 suns.}, note = {Proceedings of the 7th international conference on Crystalline Silicon Photovoltaics}, keywords = {Carrier lifetime, Degradation, Multicrystalline silicon}, pubstate = {published}, tppubtype = {article} } We examine the defect activation kinetics in block-cast high-performance multicrystalline silicon (HP mc-Si) under illumination at elevated temperature. Our lifetime analysis shows that the observed light-induced lifetime degradation consists of two separate stages: a fast stage followed by a slow stage. Our experiments reveal that both degradation stages can be fitted using a sum of two exponential decay functions. The resulting degradation rate constants depend both on the temperature and the light intensity applied during degradation. For the fast component, we determine an activation energy of (0.89 ± 0.04) eV from an Arrhenius plot of the degradation rate and for the slow component we determine a value of (0.94 ± 0.06) eV. The activation energies are relatively large, leading to a very pronounced dependence of the degradation rates on temperature. We also observe that both degradation rates show a linear dependence on the applied light intensity during degradation in the examined intensity range between 0.25 and 1.5 suns.
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T. Dullweber, H. Schulte-Huxel, S. Blankemeyer, H. Hannebauer, S. Schimanke, U. Baumann, R. Witteck, R. Peibst, M. Köntges, R. Brendel, and Y. Yao Industrial implementation of bifacial PERC+ solar cells and modules Sonstige Photovoltaics International Volume 38, (2017). Abstract | BibTeX | Schlagwörter: Solar Cells @misc{Dullweber2017c,
title = {Industrial implementation of bifacial PERC+ solar cells and modules}, author = {T Dullweber and H Schulte-Huxel and S Blankemeyer and H Hannebauer and S Schimanke and U Baumann and R Witteck and R Peibst and M Köntges and R Brendel and Y Yao}, year = {2017}, date = {2017-12-01}, abstract = {Since its first publication in 2015, the PERC+ cell concept, which is based on a passivated emitter and rear cell (PERC) design with a screen-printed Al finger grid on the rear, has been rapidly adopted by several solar cell manufacturers worldwide.}, howpublished = {Photovoltaics International Volume 38}, keywords = {Solar Cells}, pubstate = {published}, tppubtype = {misc} } Since its first publication in 2015, the PERC+ cell concept, which is based on a passivated emitter and rear cell (PERC) design with a screen-printed Al finger grid on the rear, has been rapidly adopted by several solar cell manufacturers worldwide.
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A. Morlier, M. Siebert, I. Kunze, G. Mathiak, and M. Köntges IEEE Journal of Photovoltaics 7 (6), 1710-1716 (2017), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Fluorescence, Inspection, nondestructive testing, Photovoltaic systems, reliability, solar module reliability @article{Morlier2017b,
title = {Detecting Photovoltaic Module Failures in the Field During Daytime With Ultraviolet Fluorescence Module Inspection}, author = {A Morlier and M Siebert and I Kunze and G Mathiak and M Köntges}, doi = {10.1109/JPHOTOV.2017.2756452}, issn = {2156-3381}, year = {2017}, date = {2017-11-01}, journal = {IEEE Journal of Photovoltaics}, volume = {7}, number = {6}, pages = {1710-1716}, abstract = {We present the potential of ultraviolet fluorescence imaging for the detection of function and safety failures of photovoltaic modules in the field. We apply this method to detect hotspots, mismatched cells, power-loss-inducing cracks, and we show how we use it to evaluate the crack history of a module. We present a device able to acquire fluorescence images in the field in the daytime without disconnecting the modules and with a throughput of more than 200 modules per hour for a single operator. Furthermore, we show how the technique allows for the discrimination of specific damages caused to the photovoltaic modules by sudden events such as hailstorms. We demonstrate that this method possesses an informative potential comparable to both thermography and electroluminescence together with less practical limitations.}, keywords = {Fluorescence, Inspection, nondestructive testing, Photovoltaic systems, reliability, solar module reliability}, pubstate = {published}, tppubtype = {article} } We present the potential of ultraviolet fluorescence imaging for the detection of function and safety failures of photovoltaic modules in the field. We apply this method to detect hotspots, mismatched cells, power-loss-inducing cracks, and we show how we use it to evaluate the crack history of a module. We present a device able to acquire fluorescence images in the field in the daytime without disconnecting the modules and with a throughput of more than 200 modules per hour for a single operator. Furthermore, we show how the technique allows for the discrimination of specific damages caused to the photovoltaic modules by sudden events such as hailstorms. We demonstrate that this method possesses an informative potential comparable to both thermography and electroluminescence together with less practical limitations.
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B. Min, M. Müller, H. Wagner, G. Fischer, R. Brendel, P. P. Altermatt, and H. Neuhaus A Roadmap Toward 24 % Efficient PERC Solar Cells in Industrial Mass Production Artikel IEEE Journal of Photovoltaics 7 (6), 1541-1550 (2017), ISSN: 2156-3381. Abstract | Links | BibTeX | Schlagwörter: Conductivity, Mass production, metallization, Passivated emitter and rear cell (PERC) solar cells, Photovoltaic cells, roadmap, Semiconductor device modeling, silicon, silicon solar cells @article{Min2017c,
title = {A Roadmap Toward 24 % Efficient PERC Solar Cells in Industrial Mass Production}, author = {B Min and M Müller and H Wagner and G Fischer and R Brendel and P P Altermatt and H Neuhaus}, doi = {10.1109/JPHOTOV.2017.2749007}, issn = {2156-3381}, year = {2017}, date = {2017-11-01}, journal = {IEEE Journal of Photovoltaics}, volume = {7}, number = {6}, pages = {1541-1550}, abstract = {Many manufacturers choose the passivated emitter and rear cell (PERC) approach in order to surpass the 20% cell efficiency level in mass production. In this paper, we study the efficiency potential of the PERC approach under realistic assumptions for incremental improvements of existing technologies by device simulations. Based on the most recent published experimental results, we find that the PERC structure is able to reach about 24% cell efficiency in mass production by an ongoing sequence of incremental improvements. As a guideline for future developments, we provide a method to improve cell efficiency most effectively by monitoring the current losses at the maximum power point. By means of numerical device modeling, we identify some key technologies toward 24% efficient PERC cells and provide its technology-related target requirements.}, keywords = {Conductivity, Mass production, metallization, Passivated emitter and rear cell (PERC) solar cells, Photovoltaic cells, roadmap, Semiconductor device modeling, silicon, silicon solar cells}, pubstate = {published}, tppubtype = {article} } Many manufacturers choose the passivated emitter and rear cell (PERC) approach in order to surpass the 20% cell efficiency level in mass production. In this paper, we study the efficiency potential of the PERC approach under realistic assumptions for incremental improvements of existing technologies by device simulations. Based on the most recent published experimental results, we find that the PERC structure is able to reach about 24% cell efficiency in mass production by an ongoing sequence of incremental improvements. As a guideline for future developments, we provide a method to improve cell efficiency most effectively by monitoring the current losses at the maximum power point. By means of numerical device modeling, we identify some key technologies toward 24% efficient PERC cells and provide its technology-related target requirements.
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B. A. Veith-Wolf, and J. Schmidt physica status solidi (RRL) – Rapid Research Letters 11 (11), 1700235 (2017), ISSN: 1862-6270, (1700235). Abstract | Links | BibTeX | Schlagwörter: Al2O3, Auger recombination, intrinsic recombination, minority carrier lifetime, silicon, surface passivation @article{Veith-Wolf2017,
title = {Unexpectedly High Minority-Carrier Lifetimes Exceeding 20 ms Measured on 1.4-Ω cm n-Type Silicon Wafers}, author = {B A Veith-Wolf and J Schmidt}, doi = {10.1002/pssr.201700235}, issn = {1862-6270}, year = {2017}, date = {2017-11-01}, journal = {physica status solidi (RRL) – Rapid Research Letters}, volume = {11}, number = {11}, pages = {1700235}, publisher = {WILEY?VCH Verlag Berlin GmbH}, abstract = {We measure very high minority‐carrier lifetimes exceeding 20 ms on 1.4‐Ω cm n‐type Czochralski silicon wafers passivated using plasma‐assisted atomic‐layer‐deposited Al2O3 on both wafer surfaces. The measured maximum effective lifetimes are surprisingly high as they significantly exceed the intrinsic lifetime limit previously reported in the literature. We are able to measure such high lifetimes by realizing an exceptionally homogeneous Al2O3 surface passivation on large‐area samples (12.5 × 12.5 cm2). The importance of the homogeneous passivation is demonstrated by comparison with samples of locally reduced passivation quality.}, note = {1700235}, keywords = {Al2O3, Auger recombination, intrinsic recombination, minority carrier lifetime, silicon, surface passivation}, pubstate = {published}, tppubtype = {article} } We measure very high minority‐carrier lifetimes exceeding 20 ms on 1.4‐Ω cm n‐type Czochralski silicon wafers passivated using plasma‐assisted atomic‐layer‐deposited Al2O3 on both wafer surfaces. The measured maximum effective lifetimes are surprisingly high as they significantly exceed the intrinsic lifetime limit previously reported in the literature. We are able to measure such high lifetimes by realizing an exceptionally homogeneous Al2O3 surface passivation on large‐area samples (12.5 × 12.5 cm2). The importance of the homogeneous passivation is demonstrated by comparison with samples of locally reduced passivation quality.
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S. R. Nabavi, F. Haase, E. Jansen, and R. Rolfes Solar Energy Materials and Solar Cells 170 , 263-277 (2017), ISSN: 0927-0248. Abstract | Links | BibTeX | Schlagwörter: Cofiring, Heterogeneity, Monte-Carlo simulation, Multistability, Polycrystalline silicon solar cells, Thickness uncertainty @article{Nabavi2017b,
title = {Monte-Carlo simulation of the cofiring process in polycrystalline silicon solar cells: Effects of material heterogeneity and thickness uncertainties}, author = {S R Nabavi and F Haase and E Jansen and R Rolfes}, doi = {10.1016/j.solmat.2017.06.012}, issn = {0927-0248}, year = {2017}, date = {2017-10-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {170}, pages = {263-277}, abstract = {During production, solar cells undergo significant thermomechanical loadings that lead to permanent deformations before being laminated in photovoltaic (PV) modules. One of these thermomechanical production processes is cofiring. In this work, the permanent deformation of solar cells after the cofiring process was investigated. The experimental measurements revealed a great scatter in the measured deflection at the deformed edges of the polycrystalline silicon solar cells after the cofiring process. A finite element (FE) framework was developed to investigate factors contributing to this scatter. The framework predicts the multistable response of the solar cell to the thermomechanical loading of the cofiring process. It accounts for the uncertainties arising from the heterogeneity of the polycrystalline silicon layer (grain orientations and non-uniform grain sizes) and uncertainties regarding the layer thicknesses of the silicon and aluminum paste. Employing the developed framework in a Monte-Carlo simulation the relative significance of the mentioned uncertainties on the deflection at the solar cell edge after the cofiring process was analyzed. Numerical results for a commercially produced polycrystalline silicon solar cell were compared with an analytical model and validated with experimental measurements.}, keywords = {Cofiring, Heterogeneity, Monte-Carlo simulation, Multistability, Polycrystalline silicon solar cells, Thickness uncertainty}, pubstate = {published}, tppubtype = {article} } During production, solar cells undergo significant thermomechanical loadings that lead to permanent deformations before being laminated in photovoltaic (PV) modules. One of these thermomechanical production processes is cofiring. In this work, the permanent deformation of solar cells after the cofiring process was investigated. The experimental measurements revealed a great scatter in the measured deflection at the deformed edges of the polycrystalline silicon solar cells after the cofiring process. A finite element (FE) framework was developed to investigate factors contributing to this scatter. The framework predicts the multistable response of the solar cell to the thermomechanical loading of the cofiring process. It accounts for the uncertainties arising from the heterogeneity of the polycrystalline silicon layer (grain orientations and non-uniform grain sizes) and uncertainties regarding the layer thicknesses of the silicon and aluminum paste. Employing the developed framework in a Monte-Carlo simulation the relative significance of the mentioned uncertainties on the deflection at the solar cell edge after the cofiring process was analyzed. Numerical results for a commercially produced polycrystalline silicon solar cell were compared with an analytical model and validated with experimental measurements.
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R. Peibst, Y. Larionova, Reiter. S. N. Orlowski, S. Schäfer, M. Turcu, B. Min, R. Brendel, D. Tetzlaff, J. Krügener, T. Wietler, U. Höhne, J-D. Kähler, H. Mehlich, and S. Frigge Industrial, Screen-Printed Double-Side Contacted Polo Cells Inproceedings WIP (Hrsg.): Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition, 451-454 Amsterdam, The Netherlands, (2017), ISBN: 3-936338-47-7. Abstract | Links | BibTeX | Schlagwörter: Carrier Selective Contacts, passivation, Polycrystalline Silicon (Si), Silicon Solar Cell(s), Transparent Conductive Oxide Films @inproceedings{Peibst2017,
title = {Industrial, Screen-Printed Double-Side Contacted Polo Cells}, author = {R Peibst and Y Larionova and S Reiter N Orlowski and S Schäfer and M Turcu and B Min and R Brendel and D Tetzlaff and J Krügener and T Wietler and U Höhne and J-D Kähler and H Mehlich and S Frigge }, editor = {WIP}, doi = {10.4229/EUPVSEC20172017-2DO.2.2}, isbn = {3-936338-47-7}, year = {2017}, date = {2017-09-28}, booktitle = {Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition}, pages = {451-454}, address = {Amsterdam, The Netherlands}, abstract = {We demonstrate an industrial double-side-contacted, screen-printed large area cell with POLO junctions on both sides and an in-house-measured energy conversion efficiency of 22.3 % (A = 244.15 cm2, Voc =714 mV, FF= 81.1 %, Jsc =38.5 mA/cm2). Most remarkably, this cell shows a very low series resistance < 0.05 Ωcm2, which supports previous observations of low specific junction resistance for the POLO scheme. The current limitations of the cell are (i) the low short-circuit current due to parasitic absorption in the rather thick poly-Si (30 nm), as well as in the ITO, (ii) deterioration of the recombination behavior upon TCO sputtering, and (iii) shunts near the edge due to non-adapted TCO edge-exclusion. }, keywords = {Carrier Selective Contacts, passivation, Polycrystalline Silicon (Si), Silicon Solar Cell(s), Transparent Conductive Oxide Films}, pubstate = {published}, tppubtype = {inproceedings} } We demonstrate an industrial double-side-contacted, screen-printed large area cell with POLO junctions on both sides and an in-house-measured energy conversion efficiency of 22.3 % (A = 244.15 cm2, Voc =714 mV, FF= 81.1 %, Jsc =38.5 mA/cm2). Most remarkably, this cell shows a very low series resistance < 0.05 Ωcm2, which supports previous observations of low specific junction resistance for the POLO scheme. The current limitations of the cell are (i) the low short-circuit current due to parasitic absorption in the rather thick poly-Si (30 nm), as well as in the ITO, (ii) deterioration of the recombination behavior upon TCO sputtering, and (iii) shunts near the edge due to non-adapted TCO edge-exclusion.
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D. C. Walter, V. Steckenreiter, L. Helmich, T. Pernau, and J. Schmidt WIP (Hrsg.): Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition, 377-381 Amsterdam, The Netherlands, (2017), ISBN: 3-936338-47-7. Abstract | Links | BibTeX | Schlagwörter: boron-oxygen defect, Czochralski-grown silicon, LID, Lifetime @inproceedings{Walter2017,
title = {Production-Compatible Regeneration of Boron-Doped Czochralski-Silicon in a Combined Fast-Firing and Regeneration Belt-Line Furnace}, author = {D C Walter and V Steckenreiter and L Helmich and T Pernau and J Schmidt }, editor = {WIP}, doi = {10.4229/EUPVSEC20172017-2CO.9.4}, isbn = {3-936338-47-7}, year = {2017}, date = {2017-09-27}, booktitle = {Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition}, pages = {377-381}, address = {Amsterdam, The Netherlands}, abstract = {Boron-doped Czochralski-grown silicon (Cz-Si), as used in the industrial production of solar cells today, is suffering from a light-induced degradation (LID) of the carrier lifetime during illumination. It has been known since a decade that under lab conditions, this degradation can be permanently cured by illumination at increased temperature, which has been known as ‘regeneration’ treatment. In this contribution, we examine the permanent regeneration of the carrier lifetime in standard boron-doped Cz-Si using an industrial combined fast-firing and regeneration furnace - the c.FIRE REG of centrotherm photovoltaics. Our study reveals that for an optimized firing and regeneration process, very high implied open-circuit voltages Voc.impl exceeding 740 mV are achieved on standard 1-2 cm p-type Cz-Si wafers. These very high measured Voc.impl values clearly indicate the suitability of the process for highly efficient PERC cell production. Additionally, as the c.FIRE REG furnace is realized in a belt-line configuration, which exposes each wafer for less than 70 s to the firing and regeneration conditions, our experiments clearly demonstrate the excellent suitability of the examined tool for the implementation into industrial solar cell production lines. We also demonstrate the successful application to industrial PERC solar cells produced by two different manufacturers. }, keywords = {boron-oxygen defect, Czochralski-grown silicon, LID, Lifetime}, pubstate = {published}, tppubtype = {inproceedings} } Boron-doped Czochralski-grown silicon (Cz-Si), as used in the industrial production of solar cells today, is suffering from a light-induced degradation (LID) of the carrier lifetime during illumination. It has been known since a decade that under lab conditions, this degradation can be permanently cured by illumination at increased temperature, which has been known as ‘regeneration’ treatment. In this contribution, we examine the permanent regeneration of the carrier lifetime in standard boron-doped Cz-Si using an industrial combined fast-firing and regeneration furnace - the c.FIRE REG of centrotherm photovoltaics. Our study reveals that for an optimized firing and regeneration process, very high implied open-circuit voltages Voc.impl exceeding 740 mV are achieved on standard 1-2 cm p-type Cz-Si wafers. These very high measured Voc.impl values clearly indicate the suitability of the process for highly efficient PERC cell production. Additionally, as the c.FIRE REG furnace is realized in a belt-line configuration, which exposes each wafer for less than 70 s to the firing and regeneration conditions, our experiments clearly demonstrate the excellent suitability of the examined tool for the implementation into industrial solar cell production lines. We also demonstrate the successful application to industrial PERC solar cells produced by two different manufacturers.
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G. Mathiak, N. Pfeiffer, L. Rimmelspacher, W. Herrmann, J. Althaus, F. Reil, C. Holze, and A. Morlier PV Module Sand Abrasion Testing Inproceedings WIP (Hrsg.): Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition, 1383-1390 Amsterdam, The Netherlands, (2017), ISBN: 3-936338-47-7. Abstract | Links | BibTeX | Schlagwörter: Glass Coating, Qualification and Testing, Reflectance, Sand Abrasion, Transmittance, Trickling Sand @inproceedings{Mathiak2017,
title = {PV Module Sand Abrasion Testing}, author = {G Mathiak and N Pfeiffer and L Rimmelspacher and W Herrmann and J Althaus and F Reil and C Holze and A Morlier }, editor = {WIP}, doi = {10.4229/EUPVSEC20172017-5CO.5.2}, isbn = {3-936338-47-7}, year = {2017}, date = {2017-09-27}, booktitle = {Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition}, pages = {1383-1390}, address = {Amsterdam, The Netherlands}, abstract = {Due to the high solar irradiation and the large number of sunny days the use of large PV systems in desert areas is very profitable. However, the PV modules are exposed to harsh environmental conditions such as high temperatures, high UV radiation or sandstorms. Currently there is no suitable standardized method for testing the abrasion resistance of PV modules and solar glass under sandstorm conditions. Qualification testing of PV modules for arid climate conditions will require to include a sand abrasion test and a dry cleaning resistivity test. In order to be able to assess the individual influencing factors in more detail, this work examines the sand trickling tests defined in DIN 52348 [1] and ASTM D968-05 [2] in detail. Furthermore, we developed a test facility, which can be used to simulate the impacts of desert sand on the surface of PV modules and solar glasses. Via transmittance and reflectance measurements on PV modules and solar glass sheets before and after sand abrasion tests, the samples are characterized and their resistance to desert conditions is assessed. }, keywords = {Glass Coating, Qualification and Testing, Reflectance, Sand Abrasion, Transmittance, Trickling Sand}, pubstate = {published}, tppubtype = {inproceedings} } Due to the high solar irradiation and the large number of sunny days the use of large PV systems in desert areas is very profitable. However, the PV modules are exposed to harsh environmental conditions such as high temperatures, high UV radiation or sandstorms. Currently there is no suitable standardized method for testing the abrasion resistance of PV modules and solar glass under sandstorm conditions. Qualification testing of PV modules for arid climate conditions will require to include a sand abrasion test and a dry cleaning resistivity test. In order to be able to assess the individual influencing factors in more detail, this work examines the sand trickling tests defined in DIN 52348 [1] and ASTM D968-05 [2] in detail. Furthermore, we developed a test facility, which can be used to simulate the impacts of desert sand on the surface of PV modules and solar glasses. Via transmittance and reflectance measurements on PV modules and solar glass sheets before and after sand abrasion tests, the samples are characterized and their resistance to desert conditions is assessed.
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S. Kajari-Schröder, C. Gemmel, J. Hensen, and R. Brendel Towards Multi Millisecond Spatially Homogeneous Carrier Lifetimes from Epitaxial Silicon Wafers Grown on Porous Silicon Inproceedings WIP (Hrsg.): Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition, 339-342 Amsterdam, The Netherlands, (2017), ISBN: 3-936338-47-7. Abstract | Links | BibTeX | Schlagwörter: Epitaxial Wafer, Kerfless Si, Porous Silicon @inproceedings{Kajari-Schröder2017,
title = {Towards Multi Millisecond Spatially Homogeneous Carrier Lifetimes from Epitaxial Silicon Wafers Grown on Porous Silicon}, author = {S Kajari-Schröder and C Gemmel and J Hensen and R Brendel }, editor = {WIP}, doi = {10.4229/EUPVSEC20172017-2BO.3.5}, isbn = {3-936338-47-7}, year = {2017}, date = {2017-09-26}, booktitle = {Proceedings of the 33rd European Photovoltaic Solar Energy Conference and Exhibition}, pages = {339-342}, address = {Amsterdam, The Netherlands}, abstract = {Kerfless wafering is receiving renewed attention internationally due to a) the need of PV industry to realize cost savings and to enhance resource efficiency along the value chain and b) due to the recent step by step demonstrations of key components for the implementation of kerfless wafers in mainstream photovoltaics: high electronic quality of the kerfless wafers, suitability for existing machinery (drop-in replacement), and high solar cell efficiencies. We use the porous silicon (PSI) process for the fabrication of kerfless monocrystalline silicon wafers. Here, we analyze the PSI wafer quality by analyzing the injectiondependent carrier lifetimes of the samples with infrared lifetime mappings and photo conductance decay measurements. We evaluate the reorganization of the PSI by scanning electron microscopy (SEM). We successfully lift-off 7 out of 7 epitaxial PSI wafers on an area of 10 x 10 cm2 pseudosquare. The effective lifetimes of these layers range from 836 to 1022 μs at an injection level of n=10^15 cm-3 and the lifetime is spatially homogeneous on the wafer area. }, keywords = {Epitaxial Wafer, Kerfless Si, Porous Silicon}, pubstate = {published}, tppubtype = {inproceedings} } Kerfless wafering is receiving renewed attention internationally due to a) the need of PV industry to realize cost savings and to enhance resource efficiency along the value chain and b) due to the recent step by step demonstrations of key components for the implementation of kerfless wafers in mainstream photovoltaics: high electronic quality of the kerfless wafers, suitability for existing machinery (drop-in replacement), and high solar cell efficiencies. We use the porous silicon (PSI) process for the fabrication of kerfless monocrystalline silicon wafers. Here, we analyze the PSI wafer quality by analyzing the injectiondependent carrier lifetimes of the samples with infrared lifetime mappings and photo conductance decay measurements. We evaluate the reorganization of the PSI by scanning electron microscopy (SEM). We successfully lift-off 7 out of 7 epitaxial PSI wafers on an area of 10 x 10 cm2 pseudosquare. The effective lifetimes of these layers range from 836 to 1022 μs at an injection level of n=10^15 cm-3 and the lifetime is spatially homogeneous on the wafer area.
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