Publications
2021 |
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R. C. Whitehead, K. T. VanSant, E. L. Warren, J. Buencuerpo, M. Rienäcker, R. Peibst, J. F. Geisz, and A. C. Tamboli Optimization of four terminal rear heterojunction GaAs on Si interdigitated back contact tandem solar cells Journal Article Applied Physics Letters 118 (18), 183902, (2021). Abstract | Links | BibTeX | Tags: Heterostructures, Photoconversion efficiency, Renewable energy, semiconductors, Solar Cells, solar energy @article{Whitehead2021,
title = {Optimization of four terminal rear heterojunction GaAs on Si interdigitated back contact tandem solar cells}, author = {R C Whitehead and K T VanSant and E L Warren and J Buencuerpo and M Rienäcker and R Peibst and J F Geisz and A C Tamboli}, doi = {10.1063/5.0049097}, year = {2021}, date = {2021-05-03}, journal = {Applied Physics Letters}, volume = {118}, number = {18}, pages = {183902}, abstract = {High-efficiency, four-terminal tandem solar cells composed of thin GaAs films mechanically stacked onto interdigitated back contact silicon solar cells with a glass interlayer are demonstrated. The optimal thickness of the absorber layer of a rear heterojunction GaAs subcell for use in four terminal tandem solar cells was studied. GaAs top cells with absorber layer thicknesses of 1.5, 1.9, 2.3, 2.8, and 3.5 μm were fabricated on glass and mechanically stacked onto interdigitated back-contact Si bottom cells. All tandem cells were found to have efficiencies above 30% under the AM1.5 G spectrum demonstrating a relatively weak sensitivity to thickness in the four-terminal configuration. We found the 2.8 μm absorber layer cell to have the highest top cell and tandem cell efficiency at 26.38% and 32.57%, respectively. Optical modeling with transfer matrix method for the planar top cell and Lambertian light trapping in the textured Si subcell, along with drift-diffusion Hovel equations, were used to show photon recycling enhancement to the effective diffusion length and VOC of the top cell as a result of the low-index glass interlayer.}, keywords = {Heterostructures, Photoconversion efficiency, Renewable energy, semiconductors, Solar Cells, solar energy}, pubstate = {published}, tppubtype = {article} } High-efficiency, four-terminal tandem solar cells composed of thin GaAs films mechanically stacked onto interdigitated back contact silicon solar cells with a glass interlayer are demonstrated. The optimal thickness of the absorber layer of a rear heterojunction GaAs subcell for use in four terminal tandem solar cells was studied. GaAs top cells with absorber layer thicknesses of 1.5, 1.9, 2.3, 2.8, and 3.5 μm were fabricated on glass and mechanically stacked onto interdigitated back-contact Si bottom cells. All tandem cells were found to have efficiencies above 30% under the AM1.5 G spectrum demonstrating a relatively weak sensitivity to thickness in the four-terminal configuration. We found the 2.8 μm absorber layer cell to have the highest top cell and tandem cell efficiency at 26.38% and 32.57%, respectively. Optical modeling with transfer matrix method for the planar top cell and Lambertian light trapping in the textured Si subcell, along with drift-diffusion Hovel equations, were used to show photon recycling enhancement to the effective diffusion length and VOC of the top cell as a result of the low-index glass interlayer.
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F. Haase, B. Min, C. Hollemann, J. Krügener, R. Brendel, and R. Peibst Progress in Photovoltaics: Research and Applications 29 (5), 516-523, (2021). Abstract | Links | BibTeX | Tags: IBC solar cells, local Al-p+, passivating contacts, POLO @article{Haase2021,
title = {Fully screen-printed silicon solar cells with local Al-p+ and n-type POLO interdigitated back contacts with a VOC of 716 mV and an efficiency of 23%}, author = {F Haase and B Min and C Hollemann and J Krügener and R Brendel and R Peibst}, doi = {10.1002/pip.3399}, year = {2021}, date = {2021-05-01}, journal = {Progress in Photovoltaics: Research and Applications}, volume = {29}, number = {5}, pages = {516-523}, abstract = {We demonstrate the fabrication of a fully screen-printed p-type silicon solar cell with local hole-collecting Al-alloyed (Al-p+) contacts with a record open circuit voltage of 716 mV. The solar cell is fabricated by using almost the same process equipment as PERC cells. One of the dominant recombination losses in PERC cells is the recombination in the passivated and in the contacted emitter regions that so far limit the open circuit voltage to values below 700 mV. We eliminate these loss channels by substituting the P-diffused emitter by a passivating n-type poly-Silicon on Oxide (nPOLO) contact. We place this contact on the rear side because of its otherwise strong parasitic absorption. The Al-p+ contacts are also located at the rear side to avoid front-side shading. This results in a POLO-IBC cell structure. The efficiency of the best cell so far is 23.0% with a designated area of 4 cm2 fabricated on a M2-sized wafer. Scanning electron microscopy reveals an Al-p+ thickness of less than 3.3 μm and only a few 100 nm at the contact ends, which is less than the 5 μm typically for optimized Al-p+ contacts. A comparison of measured and simulated current-voltage curves over a variation of the contact fraction extracts a high saturation current density of the Al-p+ contact of J0-Al -p+ = 2,250 fA cm−2 for the current screen-print conditions and Al-paste causing an absolute efficiency loss of 0.5%abs. The recombination at the AlOx/SiNy surface and the shunt resistance limits the cell by 0.6%abs each.}, keywords = {IBC solar cells, local Al-p+, passivating contacts, POLO}, pubstate = {published}, tppubtype = {article} } We demonstrate the fabrication of a fully screen-printed p-type silicon solar cell with local hole-collecting Al-alloyed (Al-p+) contacts with a record open circuit voltage of 716 mV. The solar cell is fabricated by using almost the same process equipment as PERC cells. One of the dominant recombination losses in PERC cells is the recombination in the passivated and in the contacted emitter regions that so far limit the open circuit voltage to values below 700 mV. We eliminate these loss channels by substituting the P-diffused emitter by a passivating n-type poly-Silicon on Oxide (nPOLO) contact. We place this contact on the rear side because of its otherwise strong parasitic absorption. The Al-p+ contacts are also located at the rear side to avoid front-side shading. This results in a POLO-IBC cell structure. The efficiency of the best cell so far is 23.0% with a designated area of 4 cm2 fabricated on a M2-sized wafer. Scanning electron microscopy reveals an Al-p+ thickness of less than 3.3 μm and only a few 100 nm at the contact ends, which is less than the 5 μm typically for optimized Al-p+ contacts. A comparison of measured and simulated current-voltage curves over a variation of the contact fraction extracts a high saturation current density of the Al-p+ contact of J0-Al -p+ = 2,250 fA cm−2 for the current screen-print conditions and Al-paste causing an absolute efficiency loss of 0.5%abs. The recombination at the AlOx/SiNy surface and the shunt resistance limits the cell by 0.6%abs each.
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B. Lim Hausaufgaben der Photovoltaik-Technologieentwicklung – Optimale Flächennutzung, nahtlose Integration, weiter sinkende Kosten Presentation/Poster Online Event, 23.04.2021, (Photovoltaiktechnologien - aktueller Stand und Ausblick (Sächsische Energieagentur – SAENA GmbH)). @misc{Lim2021b,
title = {Hausaufgaben der Photovoltaik-Technologieentwicklung – Optimale Flächennutzung, nahtlose Integration, weiter sinkende Kosten}, author = {B Lim}, year = {2021}, date = {2021-04-23}, address = {Online Event}, note = {Photovoltaiktechnologien - aktueller Stand und Ausblick (Sächsische Energieagentur – SAENA GmbH)}, keywords = {PV}, pubstate = {published}, tppubtype = {presentation} } |
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R. Peibst Towards 28 %-Efficient Si Single Junction Solar Cells with Better Passivating POLO Junctions Presentation/Poster Online Event, 22.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Peibst2021,
title = {Towards 28 %-Efficient Si Single Junction Solar Cells with Better Passivating POLO Junctions}, author = {R Peibst}, year = {2021}, date = {2021-04-22}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } |
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C. Hollemann Influence of Firing on the Interface State Density of n-Type Poly-Si Passivating Contacts Presentation/Poster Online Event, 22.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Hollemann2021,
title = {Influence of Firing on the Interface State Density of n-Type Poly-Si Passivating Contacts}, author = {C Hollemann}, year = {2021}, date = {2021-04-22}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } |
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N. Folchert Modelling the Annealing of Poly-Si/SiOx/c-Si Junctions Presentation/Poster Online Event, 22.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Folchert2021b,
title = {Modelling the Annealing of Poly-Si/SiOx/c-Si Junctions}, author = {N Folchert}, year = {2021}, date = {2021-04-22}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } |
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H. Wagner-Mohnsen Machine Learning for Optimizing Mass-Produced Industrial PERC Solar Cells Presentation/Poster Online Event, 22.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). BibTeX | Tags: Machine Learning @misc{Wagner-Mohnsen2021,
title = {Machine Learning for Optimizing Mass-Produced Industrial PERC Solar Cells}, author = {H Wagner-Mohnsen}, year = {2021}, date = {2021-04-22}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {Machine Learning}, pubstate = {published}, tppubtype = {presentation} } |
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L. Helmich Impact of Hydrogen on the Boron-oxygen Degradation and Regeneration Kinetics Presentation/Poster Online Event, 21.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Helmich2021,
title = {Impact of Hydrogen on the Boron-oxygen Degradation and Regeneration Kinetics}, author = {L Helmich}, year = {2021}, date = {2021-04-21}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {Hydrogen}, pubstate = {published}, tppubtype = {presentation} } |
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D. Bredemeier Fast Calculation of Large-Scale Photovoltaic Roof-Top Potentials Using Backwards-Raytracing and Machine Learning Presentation/Poster Online Event, 21.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). BibTeX | Tags: raytracing @misc{Bredemeier2021,
title = {Fast Calculation of Large-Scale Photovoltaic Roof-Top Potentials Using Backwards-Raytracing and Machine Learning}, author = {D Bredemeier}, year = {2021}, date = {2021-04-21}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {raytracing}, pubstate = {published}, tppubtype = {presentation} } |
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M. Stöhr, J. Aprojanz, R. Brendel, and T. Dullweber Firing-Stable PECVD SiOxNy/n-Poly-Si Surface Passivation for Silicon Solar Cells Journal Article Forthcoming ACS Applied Energy Materials Forthcoming. Abstract | Links | BibTeX | Tags: blistering, firing stability, passivating contacts, PECVD deposition, silicon solar cells, SiOxNy/poly-Si @article{Stöhr2021,
title = {Firing-Stable PECVD SiOxNy/n-Poly-Si Surface Passivation for Silicon Solar Cells}, author = {M Stöhr and J Aprojanz and R Brendel and T Dullweber}, doi = {10.1021/acsaem.1c00265}, year = {2021}, date = {2021-04-21}, journal = {ACS Applied Energy Materials}, publisher = {American Chemical Society}, abstract = {Passivating contacts based on SiOx/poly-Si exhibit excellent contact and surface passivation properties enabling very high solar cell conversion efficiencies. In this paper, we investigate and optimize the plasma-enhanced chemical vapor deposition (PECVD) of SiOxNy/n-a-Si stacks, their subsequent annealing to SiOxNy/n-poly-Si stacks followed by PECVD SiNx deposition and firing. We eliminate blistering of the poly-Si layer by enabling a controlled hydrogen out-diffusion during the annealing step. Whereas the J0 of thermal SiOx/n-poly-Si stacks degrade after firing, PECVD SiOxNy/n-poly-Si stacks exhibit excellent firing stability enabling J0 values down to 1.3 fA/cm2 after firing which corresponds to an outstanding implied VOC of 744 mV. The application of different hydrogenation processes to the thermal SiOx/n-poly-Si and PECVD SiOxNy/n-poly-Si stacks reveals that both stacks achieve excellent passivation properties with J0 = 1.5 fA/cm2 after maximum hydrogenation. However, only the PECVD SiOxNy/n-poly-Si stack maintains this excellent surface passivation after firing possibly due to a superior capability to retain the hydrogen at the c-Si/SiOxNy interface during firing and thus demonstrates the potential as a future manufacturing process sequence.}, keywords = {blistering, firing stability, passivating contacts, PECVD deposition, silicon solar cells, SiOxNy/poly-Si}, pubstate = {forthcoming}, tppubtype = {article} } Passivating contacts based on SiOx/poly-Si exhibit excellent contact and surface passivation properties enabling very high solar cell conversion efficiencies. In this paper, we investigate and optimize the plasma-enhanced chemical vapor deposition (PECVD) of SiOxNy/n-a-Si stacks, their subsequent annealing to SiOxNy/n-poly-Si stacks followed by PECVD SiNx deposition and firing. We eliminate blistering of the poly-Si layer by enabling a controlled hydrogen out-diffusion during the annealing step. Whereas the J0 of thermal SiOx/n-poly-Si stacks degrade after firing, PECVD SiOxNy/n-poly-Si stacks exhibit excellent firing stability enabling J0 values down to 1.3 fA/cm2 after firing which corresponds to an outstanding implied VOC of 744 mV. The application of different hydrogenation processes to the thermal SiOx/n-poly-Si and PECVD SiOxNy/n-poly-Si stacks reveals that both stacks achieve excellent passivation properties with J0 = 1.5 fA/cm2 after maximum hydrogenation. However, only the PECVD SiOxNy/n-poly-Si stack maintains this excellent surface passivation after firing possibly due to a superior capability to retain the hydrogen at the c-Si/SiOxNy interface during firing and thus demonstrates the potential as a future manufacturing process sequence.
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M. Rienäcker Measuring Selectivity and Extraction Efficiency: the Three-Terminal Suns-VOC Method Applied to an n-c-Si/SiOy/TiOx/Al Junction Presentation/Poster Online Event, 20.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). BibTeX | Tags: selectivity @misc{Rienäcker2021,
title = {Measuring Selectivity and Extraction Efficiency: the Three-Terminal Suns-VOC Method Applied to an n-c-Si/SiOy/TiOx/Al Junction}, author = {M Rienäcker}, year = {2021}, date = {2021-04-20}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {selectivity}, pubstate = {published}, tppubtype = {presentation} } |
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N. Folchert Easy-to-Apply Contact Resistance Measurements of the Interfacial Oxide in Poly-Si/SiOx/c-Si Junctions – Revisiting the Cox & Strack Formula Presentation/Poster Online Event, 20.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Folchert2021,
title = {Easy-to-Apply Contact Resistance Measurements of the Interfacial Oxide in Poly-Si/SiOx/c-Si Junctions – Revisiting the Cox & Strack Formula }, author = {N Folchert}, year = {2021}, date = {2021-04-20}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } |
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B. Min Impact of Dielectric Capping Layer Thickness on the Contact Formation between n+-type Passivating Contacts and Screen-printed Fire-through Silver Pastes Presentation/Poster Online Event, 20.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Min2021b,
title = {Impact of Dielectric Capping Layer Thickness on the Contact Formation between n+-type Passivating Contacts and Screen-printed Fire-through Silver Pastes}, author = {B Min}, year = {2021}, date = {2021-04-20}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {POLO BJ}, pubstate = {published}, tppubtype = {presentation} } |
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S. Baumann Influence of Encapsulation Process Temperature on the Performance of Perovskite Mini Modules Presentation/Poster Online Event, 20.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). BibTeX | Tags: Modules, perovskite @misc{Baumann2021,
title = {Influence of Encapsulation Process Temperature on the Performance of Perovskite Mini Modules}, author = {S Baumann}, year = {2021}, date = {2021-04-20}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {Modules, perovskite}, pubstate = {published}, tppubtype = {presentation} } |
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M. Winter Understanding Light-Induced Degradation Effects in Ga-doped Cz-Si and B-doped FZ-Si Materials Presentation/Poster Online Event, 20.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Winter2021,
title = {Understanding Light-Induced Degradation Effects in Ga-doped Cz-Si and B-doped FZ-Si Materials}, author = {M Winter}, year = {2021}, date = {2021-04-20}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {Ga, LID}, pubstate = {published}, tppubtype = {presentation} } |
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M. Winter, D. C. Walter, and J. Schmidt Carrier Lifetime Degradation and Regeneration in Gallium- and Boron-Doped Monocrystalline Silicon Materials Journal Article Forthcoming IEEE Journal of Photovoltaics 1-7, Forthcoming. Abstract | Links | BibTeX | Tags: Carrier lifetime, Degradation, gallium, light-induced degradation (LID), regeneration, Silicon (Si) @article{Winter2021b,
title = {Carrier Lifetime Degradation and Regeneration in Gallium- and Boron-Doped Monocrystalline Silicon Materials}, author = {M Winter and D C Walter and J Schmidt}, doi = {10.1109/JPHOTOV.2021.3070474}, year = {2021}, date = {2021-04-20}, journal = {IEEE Journal of Photovoltaics}, pages = {1-7}, abstract = {In this article, carrier lifetime degradation phenomena on fired gallium-doped Czochralski-grown silicon (Cz-Si:Ga) and boron-doped float-zone silicon (FZ-Si:B) are observed. We examine lifetime degradation and regeneration as a function of illumination intensity and temperature and observe qualitatively similar degradation effects in both material classes, which are triggered by a fast-firing high-temperature step. Charge carrier injection, e.g., through illumination, is required to activate the defects responsible for degradation. The extent of degradation increases with increasing temperature, which is untypical for degradation effects reported before. Despite different degradation time constants are measured for Cz-Si:Ga and FZ-Si:B, the activation energies are for both materials in the narrow range (0.58±0.04) eV . The extracted activation energy is quite different compared with other degradation effects in silicon, suggesting a novel defect formation mechanism. Since the lifetime degradation is triggered by the fast-firing of the silicon wafers during the presence of a hydrogen-rich dielectric at the surface, the involvement of hydrogen in the defect reaction is very likely. During prolonged illumination at elevated temperature (135 °C), we observe a permanent regeneration of the lifetime, whereas at temperatures close to room temperature (36 °C), the defect deactivation is only temporary.}, keywords = {Carrier lifetime, Degradation, gallium, light-induced degradation (LID), regeneration, Silicon (Si)}, pubstate = {forthcoming}, tppubtype = {article} } In this article, carrier lifetime degradation phenomena on fired gallium-doped Czochralski-grown silicon (Cz-Si:Ga) and boron-doped float-zone silicon (FZ-Si:B) are observed. We examine lifetime degradation and regeneration as a function of illumination intensity and temperature and observe qualitatively similar degradation effects in both material classes, which are triggered by a fast-firing high-temperature step. Charge carrier injection, e.g., through illumination, is required to activate the defects responsible for degradation. The extent of degradation increases with increasing temperature, which is untypical for degradation effects reported before. Despite different degradation time constants are measured for Cz-Si:Ga and FZ-Si:B, the activation energies are for both materials in the narrow range (0.58±0.04) eV . The extracted activation energy is quite different compared with other degradation effects in silicon, suggesting a novel defect formation mechanism. Since the lifetime degradation is triggered by the fast-firing of the silicon wafers during the presence of a hydrogen-rich dielectric at the surface, the involvement of hydrogen in the defect reaction is very likely. During prolonged illumination at elevated temperature (135 °C), we observe a permanent regeneration of the lifetime, whereas at temperatures close to room temperature (36 °C), the defect deactivation is only temporary.
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F. Haase 23%-Efficient Screen-Printed IBC Cells on Cz-Grown Silicon with n-Type Poly-Si Passivating Contact and Al-alloyed p-Type Contact Presentation/Poster Online Event, 19.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). @misc{Haase2021b,
title = {23%-Efficient Screen-Printed IBC Cells on Cz-Grown Silicon with n-Type Poly-Si Passivating Contact and Al-alloyed p-Type Contact}, author = {F Haase}, year = {2021}, date = {2021-04-19}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {IBC, POLO}, pubstate = {published}, tppubtype = {presentation} } |
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C. Schinke Measuring the Spectral Irradiance of Solar Simulators Presentation/Poster Online Event, 19.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics). BibTeX | Tags: Spectral Irradiance @misc{Schinke2021b,
title = {Measuring the Spectral Irradiance of Solar Simulators}, author = {C Schinke}, year = {2021}, date = {2021-04-19}, address = {Online Event}, note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics}, keywords = {Spectral Irradiance}, pubstate = {published}, tppubtype = {presentation} } |
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B. Min, M. Müller, B. Wolpensinger, G. Fischer, P. Palinginis, D. H. Neuhaus, and R. Brendel Impact of Local Back-Surface-Field Thickness Variation on Performance of PERC Solar Cells Journal Article Forthcoming IEEE Journal of Photovoltaics 1-6, Forthcoming, ISSN: 2156-3403. Abstract | Links | BibTeX | Tags: Local back-surface-field (BSF) thickness, open-circuit voltage, Passivated emitter and rear cell (PERC) solar cells @article{Min2021,
title = {Impact of Local Back-Surface-Field Thickness Variation on Performance of PERC Solar Cells}, author = {B Min and M Müller and B Wolpensinger and G Fischer and P Palinginis and D H Neuhaus and R Brendel}, doi = {10.1109/JPHOTOV.2021.3068603}, issn = {2156-3403}, year = {2021}, date = {2021-04-13}, journal = {IEEE Journal of Photovoltaics}, pages = {1-6}, abstract = {This article investigates the impact of the back-surface-field (BSF) thickness variation within a local aluminum contact on the performance of passivated emitter and rear contact solar cells. A significant difference of BSF thickness between contact endings and the center of dash-shaped contacts is verified experimentally by a comprehensive statistical analysis using scanning electron microscopy. The impact of local BSF thickness differences on the cell performance is studied with 3-D technology computer-aided design (TCAD) device simulations. Several device parameters such as BSF thicknesses, the doping concentration in the BSF profile at rear contacts, or the metallized area fraction at the cell rear side are varied. Our simulation study shows that the open-circuit voltage is mainly affected by locally reduced BSF thicknesses, resulting in an efficiency loss up to 0.14%$_abs$ or 0.84%$_abs$, respectively, if an area fraction of 1% or 20% within a local contact has reduced BSF thicknesses. This effect can be minimized either by reducing the metallized area fraction at the cell rear side or by increasing the doping concentration in the BSF profile at aluminum rear contacts. In addition, we demonstrate that the 3-D simulations can be approximated with 2-D simulations by applying a single doping profile with an average BSF thickness, calculated with the harmonic mean.}, keywords = {Local back-surface-field (BSF) thickness, open-circuit voltage, Passivated emitter and rear cell (PERC) solar cells}, pubstate = {forthcoming}, tppubtype = {article} } This article investigates the impact of the back-surface-field (BSF) thickness variation within a local aluminum contact on the performance of passivated emitter and rear contact solar cells. A significant difference of BSF thickness between contact endings and the center of dash-shaped contacts is verified experimentally by a comprehensive statistical analysis using scanning electron microscopy. The impact of local BSF thickness differences on the cell performance is studied with 3-D technology computer-aided design (TCAD) device simulations. Several device parameters such as BSF thicknesses, the doping concentration in the BSF profile at rear contacts, or the metallized area fraction at the cell rear side are varied. Our simulation study shows that the open-circuit voltage is mainly affected by locally reduced BSF thicknesses, resulting in an efficiency loss up to 0.14%$_abs$ or 0.84%$_abs$, respectively, if an area fraction of 1% or 20% within a local contact has reduced BSF thicknesses. This effect can be minimized either by reducing the metallized area fraction at the cell rear side or by increasing the doping concentration in the BSF profile at aluminum rear contacts. In addition, we demonstrate that the 3-D simulations can be approximated with 2-D simulations by applying a single doping profile with an average BSF thickness, calculated with the harmonic mean.
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S. Schäfer, A. Mercker, A. Köhler, T. Neubert, L. Mettner, B. Wolpensinger, V. Mertens, and R. Peibst Role of oxygen in the UV-ps laser triggered amorphization of poly-Si for Si solar cells with local passivated contacts Journal Article Journal of Applied Physics 129 (13), 133103, (2021). Abstract | Links | BibTeX | Tags: Chemical elements, Chemical processes, electric measurements, Lasers, optical properties, passivation, Semiconductor materials, silicon, Solar Cells, Transmission electron microscopy @article{Schäfer2021,
title = {Role of oxygen in the UV-ps laser triggered amorphization of poly-Si for Si solar cells with local passivated contacts}, author = {S Schäfer and A Mercker and A Köhler and T Neubert and L Mettner and B Wolpensinger and V Mertens and R Peibst}, doi = {10.1063/5.0045829}, year = {2021}, date = {2021-04-07}, journal = {Journal of Applied Physics}, volume = {129}, number = {13}, pages = {133103}, abstract = {In recent years, poly-Si based passivated contacts elevated the conversion efficiencies of crystalline Si solar cells to levels of 26%abs due to their outstanding electrical surface passivation performance and current transport characteristics. A major associated challenge, however, is the large parasitic light absorption within the doped poly-Si, regardless if the contacts are applied on the front and/or on the rear side of the solar cell. It, therefore, might be beneficial to confine the passivated contacts to local regions underneath the metal contacts. We present an effective and flexible laser-based approach to structure the poly-Si layer after its full-area deposition. Laser pulses with a pulse duration of 9 ps and a wavelength of 355 nm trigger an amorphization of the poly-Si surface. The minimum threshold fluence for amorphization is between 89 and 129 mJ/cm2. The a-Si layer, which is laterally homogeneous and up to (33 ± 4) nm in thickness, works as an etch barrier in an alkaline solution. The most robust barrier corresponding to the maximum thickness of the a-Si layer is found for a fluence of (270 ± 30) mJ/cm2. Besides the impact of the laser fluence on the etch resistiveness of the modified poly-Si layer, we study the role of oxygen during the laser process. We find that oxygen becomes incorporated into the material for certain laser fluences, which results in a more robust etch barrier. The amount of oxygen incorporated is below 3 wt. %. Eventually, we present a phenomenological model of our findings.}, keywords = {Chemical elements, Chemical processes, electric measurements, Lasers, optical properties, passivation, Semiconductor materials, silicon, Solar Cells, Transmission electron microscopy}, pubstate = {published}, tppubtype = {article} } In recent years, poly-Si based passivated contacts elevated the conversion efficiencies of crystalline Si solar cells to levels of 26%abs due to their outstanding electrical surface passivation performance and current transport characteristics. A major associated challenge, however, is the large parasitic light absorption within the doped poly-Si, regardless if the contacts are applied on the front and/or on the rear side of the solar cell. It, therefore, might be beneficial to confine the passivated contacts to local regions underneath the metal contacts. We present an effective and flexible laser-based approach to structure the poly-Si layer after its full-area deposition. Laser pulses with a pulse duration of 9 ps and a wavelength of 355 nm trigger an amorphization of the poly-Si surface. The minimum threshold fluence for amorphization is between 89 and 129 mJ/cm2. The a-Si layer, which is laterally homogeneous and up to (33 ± 4) nm in thickness, works as an etch barrier in an alkaline solution. The most robust barrier corresponding to the maximum thickness of the a-Si layer is found for a fluence of (270 ± 30) mJ/cm2. Besides the impact of the laser fluence on the etch resistiveness of the modified poly-Si layer, we study the role of oxygen during the laser process. We find that oxygen becomes incorporated into the material for certain laser fluences, which results in a more robust etch barrier. The amount of oxygen incorporated is below 3 wt. %. Eventually, we present a phenomenological model of our findings.
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M-U. Halbich, and J. Schmidt Extraction of PEDOT:PSS/c-Si Junction Properties by Modeling of Injection-Dependent Lifetime Measurements Including Depletion Region Modulation Journal Article physica status solidi (RRL) – Rapid Research Letters 15 (4), 2100008, (2021). Abstract | Links | BibTeX | Tags: carrier lifetimes, depletion region modulation, heterojunctions, PEDOT:PSS, silicon @article{Halbich2021,
title = {Extraction of PEDOT:PSS/c-Si Junction Properties by Modeling of Injection-Dependent Lifetime Measurements Including Depletion Region Modulation}, author = {M-U Halbich and J Schmidt}, doi = {10.1002/pssr.202100008}, year = {2021}, date = {2021-04-01}, journal = {physica status solidi (RRL) – Rapid Research Letters}, volume = {15}, number = {4}, pages = {2100008}, abstract = {The carrier lifetime of n-type silicon wafers coated with the conducting polymer PEDOT:PSS as a function of the excess carrier concentration Δp within the wafer is characterized using the quasi-steady-state photoconductance (QSSPC) method, and a drastic increase in the measured apparent lifetime τapp with decreasing Δp is observed. The observed increase with the depletion region modulation (DRM) effect is explained, as PEDOT:PSS-coated p-type silicon wafers do not show any increase in lifetime toward low injection levels. By modeling the measured τapp(Δp) curves on n-type silicon including interface recombination as well as the DRM effect, the interface recombination velocity as well as the band bending Ψs within the silicon induced by PEDOT:PSS are able to be extracted. The impact of adding sorbitol to the PEDOT:PSS dispersion on the τapp(Δp) curves is examined, and it is demonstrated that the admixture of sorbitol improves chemical interface passivation but leaves the band bending within the silicon bulk toward the PEDOT:PSS/c-Si interface unaffected.}, keywords = {carrier lifetimes, depletion region modulation, heterojunctions, PEDOT:PSS, silicon}, pubstate = {published}, tppubtype = {article} } The carrier lifetime of n-type silicon wafers coated with the conducting polymer PEDOT:PSS as a function of the excess carrier concentration Δp within the wafer is characterized using the quasi-steady-state photoconductance (QSSPC) method, and a drastic increase in the measured apparent lifetime τapp with decreasing Δp is observed. The observed increase with the depletion region modulation (DRM) effect is explained, as PEDOT:PSS-coated p-type silicon wafers do not show any increase in lifetime toward low injection levels. By modeling the measured τapp(Δp) curves on n-type silicon including interface recombination as well as the DRM effect, the interface recombination velocity as well as the band bending Ψs within the silicon induced by PEDOT:PSS are able to be extracted. The impact of adding sorbitol to the PEDOT:PSS dispersion on the τapp(Δp) curves is examined, and it is demonstrated that the admixture of sorbitol improves chemical interface passivation but leaves the band bending within the silicon bulk toward the PEDOT:PSS/c-Si interface unaffected.
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R. Peibst Still in the game Journal Article Nature Energy 6 (4), 333-334, (2021), ISSN: 2058-7546. Abstract | Links | BibTeX | Tags: solar cell @article{Peibst2021b,
title = {Still in the game}, author = {R Peibst}, doi = {10.1038/s41560-021-00822-9}, issn = {2058-7546}, year = {2021}, date = {2021-04-01}, journal = {Nature Energy}, volume = {6}, number = {4}, pages = {333-334}, abstract = {The current mainstream photovoltaic technology used in industry has a power conversion efficiency above 23% in mass production but major further improvements are challenging. Researchers now demonstrate a 26% efficiency by implementing passivating contacts on double-side contacted solar cells.}, keywords = {solar cell}, pubstate = {published}, tppubtype = {article} } The current mainstream photovoltaic technology used in industry has a power conversion efficiency above 23% in mass production but major further improvements are challenging. Researchers now demonstrate a 26% efficiency by implementing passivating contacts on double-side contacted solar cells.
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P. Bayerl, N. Folchert, J. Bayer, M. Dzinnik, C. Hollemann, R. Brendel, R. Peibst, and R. J. Haug Contacting a single nanometer-sized pinhole in the interfacial oxide of a poly-silicon on oxide (POLO) solar cell junction Journal Article Forthcoming Progress in Photovoltaics: Research and Applications Forthcoming. Abstract | Links | BibTeX | Tags: Pinhole transport, POLO junction, record energy conversion efficiency, Silicon solar cell @article{Bayerl0000,
title = {Contacting a single nanometer-sized pinhole in the interfacial oxide of a poly-silicon on oxide (POLO) solar cell junction}, author = {P Bayerl and N Folchert and J Bayer and M Dzinnik and C Hollemann and R Brendel and R Peibst and R J Haug}, doi = {10.1002/pip.3417}, year = {2021}, date = {2021-03-30}, journal = {Progress in Photovoltaics: Research and Applications}, abstract = {Abstract The electrical current through poly-Si on oxide (POLO) solar cells is mediated by tunneling and by nanometer-sized pinholes in the interfacial oxide. To distinguish the two processes, a POLO junction with a measured pinhole density of 1 × 107 cm−2 is contacted by different contact areas ranging from 1 μm2 to 2.5 × 105 μm2, and the temperature-dependent current–voltage curves are measured for the different devices. Model regressions to the measured curves, their temperature dependence, and the quantized value of contact resistances indicate average numbers of pinholes per device corresponding to the expected pinhole density. For the small contacts, the different transport processes can be studied separately, which facilitates further improvements in respect to the present-day POLO junctions. Single-pinhole transport is found for one of the contacts with an area of 1 μm2. Random telegraph noise observed for this device in the current–voltage characteristics shows a high sensitivity to single charges.}, keywords = {Pinhole transport, POLO junction, record energy conversion efficiency, Silicon solar cell}, pubstate = {forthcoming}, tppubtype = {article} } Abstract The electrical current through poly-Si on oxide (POLO) solar cells is mediated by tunneling and by nanometer-sized pinholes in the interfacial oxide. To distinguish the two processes, a POLO junction with a measured pinhole density of 1 × 107 cm−2 is contacted by different contact areas ranging from 1 μm2 to 2.5 × 105 μm2, and the temperature-dependent current–voltage curves are measured for the different devices. Model regressions to the measured curves, their temperature dependence, and the quantized value of contact resistances indicate average numbers of pinholes per device corresponding to the expected pinhole density. For the small contacts, the different transport processes can be studied separately, which facilitates further improvements in respect to the present-day POLO junctions. Single-pinhole transport is found for one of the contacts with an area of 1 μm2. Random telegraph noise observed for this device in the current–voltage characteristics shows a high sensitivity to single charges.
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B. Lim Solarenergienutzung an Gebäuden Presentation/Poster Online Event, 25.03.2021, (Alles wird Kraftwerk - Webinar-Reihe "innovativ jetzt - Forschen für Nachhaltigkeit"). @misc{Lim2021,
title = {Solarenergienutzung an Gebäuden}, author = {B Lim}, year = {2021}, date = {2021-03-25}, address = {Online Event}, note = {Alles wird Kraftwerk - Webinar-Reihe "innovativ jetzt - Forschen für Nachhaltigkeit"}, keywords = {Gebäude}, pubstate = {published}, tppubtype = {presentation} } |
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C. Schinke Uncertainty analysis for spectroradiometer measurements of direct solar irradiation Presentation/Poster Online Event, 16.03.2021, (9th PV-Outdoor-Spectral Measurement Mini Workshop). BibTeX | Tags: spectroradiometer @misc{Schinke2021,
title = {Uncertainty analysis for spectroradiometer measurements of direct solar irradiation}, author = {C Schinke}, year = {2021}, date = {2021-03-16}, address = {Online Event}, note = {9th PV-Outdoor-Spectral Measurement Mini Workshop}, keywords = {spectroradiometer}, pubstate = {published}, tppubtype = {presentation} } |