Publications
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D. Hinken, I. Kröger, S. Winter, R. Brendel, and K. Bothe Determining the spectral responsivity of solar cells under standard test conditions Journal Article Measurement Science and Technology 30 (12), 125008, (2019). Abstract | Links | BibTeX | Tags: @article{Hinken2019,
title = {Determining the spectral responsivity of solar cells under standard test conditions}, author = {D Hinken and I Kröger and S Winter and R Brendel and K Bothe}, doi = {10.1088/1361-6501/ab34ef}, year = {2019}, date = {2019-12-01}, journal = {Measurement Science and Technology}, volume = {30}, number = {12}, pages = {125008}, publisher = {IOP Publishing}, abstract = {The spectral responsivity of solar cells is widely used for cell analysis or calibration purposes. According to the IEC60904-8:2014 standard, the reference method for the determination of is the complete differential spectral responsivity approach. For this approach, the differential spectral responsivity is measured as a function of wavelength and bias irradiance. To obtain the spectral responsivity related to standard test conditions the IEC60904-8:2014 standard recommends to integrate via bias current for each wavelength. We show that this integration is wrong. It lacks analytical derivation and provides faulty curves for non-linear solar cells. We prove analytically and by means of simulations that the correct way of calculation is either the integration of via the bias irradiance or the integration of via the bias current , with being the AMx-weighted (e.g. AM1.5G or AM1.5D) differential responsivity. A simulation of the differential spectral responsivity of a strongly non-linear solar cell demonstrates deviations of up to 30% for (the wrong) integration of via at some wavelengths, corresponding to a deviation in the short-circuit current of up to 3.0%.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The spectral responsivity of solar cells is widely used for cell analysis or calibration purposes. According to the IEC60904-8:2014 standard, the reference method for the determination of is the complete differential spectral responsivity approach. For this approach, the differential spectral responsivity is measured as a function of wavelength and bias irradiance. To obtain the spectral responsivity related to standard test conditions the IEC60904-8:2014 standard recommends to integrate via bias current for each wavelength. We show that this integration is wrong. It lacks analytical derivation and provides faulty curves for non-linear solar cells. We prove analytically and by means of simulations that the correct way of calculation is either the integration of via the bias irradiance or the integration of via the bias current , with being the AMx-weighted (e.g. AM1.5G or AM1.5D) differential responsivity. A simulation of the differential spectral responsivity of a strongly non-linear solar cell demonstrates deviations of up to 30% for (the wrong) integration of via at some wavelengths, corresponding to a deviation in the short-circuit current of up to 3.0%.
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C. Gemmel, J. Hensen, S. Kajari-Schröder, and R. Brendel Detachment yield statistics for kerfless wafering using the porous silicon process Journal Article Solar Energy Materials and Solar Cells 202 , 110061, (2019), ISSN: 0927-0248. Abstract | Links | BibTeX | Tags: Detachment probability, Porous silicon process, Statistical evaluation, Yield @article{Gemmel2019c,
title = {Detachment yield statistics for kerfless wafering using the porous silicon process}, author = {C Gemmel and J Hensen and S Kajari-Schröder and R Brendel}, doi = {10.1016/j.solmat.2019.110061}, issn = {0927-0248}, year = {2019}, date = {2019-11-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {202}, pages = {110061}, abstract = {The porous silicon (PSI) process is a wafering method to fabricate high quality kerfless crystalline Si wafers by epitaxial wafer growth on porous Si and subsequent detachment from a reusable substrate wafer. The process yield is a key parameter for the economic viability of the PSI process. We experimentally demonstrate the detachment of 59 out of 62 PSI wafers with a size of 10 × 10 cm2, and separation layer etch current densities of 105–120 mA/cm2 for electrochemically etching the porous Si, and for substrate wafers with a resistivity of 15.7–16.9 mΩcm. We discuss the statistics of how to deduce a detachment probability from this. From our experiments, we determine a detachment yield of at least 88% with an error probability of 5%. The demonstration of a 99% detachment yield with an error probability of 5% would require at least 300 successfully detached wafers with no failed detachment. Samples have a minority carrier density ranging from 1 to 1.7 ms before any external gettering, which demonstrates the high electric quality of the PSI wafers.}, keywords = {Detachment probability, Porous silicon process, Statistical evaluation, Yield}, pubstate = {published}, tppubtype = {article} } The porous silicon (PSI) process is a wafering method to fabricate high quality kerfless crystalline Si wafers by epitaxial wafer growth on porous Si and subsequent detachment from a reusable substrate wafer. The process yield is a key parameter for the economic viability of the PSI process. We experimentally demonstrate the detachment of 59 out of 62 PSI wafers with a size of 10 × 10 cm2, and separation layer etch current densities of 105–120 mA/cm2 for electrochemically etching the porous Si, and for substrate wafers with a resistivity of 15.7–16.9 mΩcm. We discuss the statistics of how to deduce a detachment probability from this. From our experiments, we determine a detachment yield of at least 88% with an error probability of 5%. The demonstration of a 99% detachment yield with an error probability of 5% would require at least 300 successfully detached wafers with no failed detachment. Samples have a minority carrier density ranging from 1 to 1.7 ms before any external gettering, which demonstrates the high electric quality of the PSI wafers.
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Y. Louvet, S. Fischer, S. Furbo, F. Giovannetti, S. Helbig, M. Köhl, D. Mugnier, D. Philippen, F. Veynandt, and K. Vajen Economic comparison of reference solar thermal systems for households in five European countries Journal Article Solar Energy 193 , 85 - 94, (2019), ISSN: 0038-092X. Abstract | Links | BibTeX | Tags: Energy economics, Solar thermal energy in Europe @article{Louvet2019b,
title = {Economic comparison of reference solar thermal systems for households in five European countries}, author = {Y Louvet and S Fischer and S Furbo and F Giovannetti and S Helbig and M Köhl and D Mugnier and D Philippen and F Veynandt and K Vajen}, doi = {10.1016/j.solener.2019.09.019}, issn = {0038-092X}, year = {2019}, date = {2019-11-01}, journal = {Solar Energy}, volume = {193}, pages = {85 - 94}, abstract = {This study presents a methodology developed in the framework of Task54 of the Solar Heating and Cooling (SHC) Program of the International Energy Agency (IEA) to calculate the heat cost per kWh final energy of solar thermal systems. Based on the concept of levelized cost of energy, three indicators are introduced depicting the heat cost of the solar part of the heating system only (LCoHsol,fin), the conventional part (LCoHconv,fin) or the overall solar assisted heating system (LCoHov,fin). The LCoHov,fin enables a comparison with other heating systems using different technologies. Applied to eleven residential systems in five European countries, the results show that the heat cost differs widely, depending on countries and system types. The solar heating system raises the heat cost of the overall solar assisted heating system compared to a reference system without solar assistance (subsidies are not considered) in most studied cases, but some solar domestic hot water systems and solar heating systems for multi-family houses are close to parity under current economic conditions and the assumptions considered in the paper. This work also highlights the importance of calculating the heat cost with a standardized methodology to enable a comparison between different systems.}, keywords = {Energy economics, Solar thermal energy in Europe}, pubstate = {published}, tppubtype = {article} } This study presents a methodology developed in the framework of Task54 of the Solar Heating and Cooling (SHC) Program of the International Energy Agency (IEA) to calculate the heat cost per kWh final energy of solar thermal systems. Based on the concept of levelized cost of energy, three indicators are introduced depicting the heat cost of the solar part of the heating system only (LCoHsol,fin), the conventional part (LCoHconv,fin) or the overall solar assisted heating system (LCoHov,fin). The LCoHov,fin enables a comparison with other heating systems using different technologies. Applied to eleven residential systems in five European countries, the results show that the heat cost differs widely, depending on countries and system types. The solar heating system raises the heat cost of the overall solar assisted heating system compared to a reference system without solar assistance (subsidies are not considered) in most studied cases, but some solar domestic hot water systems and solar heating systems for multi-family houses are close to parity under current economic conditions and the assumptions considered in the paper. This work also highlights the importance of calculating the heat cost with a standardized methodology to enable a comparison between different systems.
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A. Čampa, F. Smole, N. Folchert, T. Wietler, B. Min, R. Brendel, and M. Topič Detailed Analysis and Understanding of the Transport Mechanism of Poly-Si-Based Carrier Selective Junctions Journal Article Forthcoming IEEE Journal of Photovoltaics Forthcoming. Abstract | Links | BibTeX | Tags: Carrier-selective junctions, numerical simulations, pinholes, polysilicon on oxide, Tunneling @article{Čampa2019,
title = {Detailed Analysis and Understanding of the Transport Mechanism of Poly-Si-Based Carrier Selective Junctions}, author = {A Čampa and F Smole and N Folchert and T Wietler and B Min and R Brendel and M Topič}, doi = {10.1109/JPHOTOV.2019.2943610}, year = {2019}, date = {2019-10-14}, journal = {IEEE Journal of Photovoltaics}, abstract = {We investigate the transport mechanism of poly-Si-based carrier-selective junctions using the two-dimensional numerical semiconductor device simulations. The detailed transport model considers the charge carrier transport through the pinholes as well as tunneling through a very thin silicon oxide simultaneously. For the verification of the simulation model, the complete temperature dependent transfer length method is modeled and its results are verified with measurements of two different samples. By means of rigorous simulations, the influence of different pinhole geometrical and material parameters on junction resistivity are investigated and explained in detail. From the presented results, the fundamental understanding needed for optimizing the poly-Si-based carrier selective junction in respect to the main design parameters such as doping level in poly-Si, annealing time, silicon oxide thickness, and pinhole density is given. The detailed analysis shows the pinhole channel plays the most crucial role in the design of poly-Si-based carrier-selective junctions if the silicon oxide layer thickness is larger than 2 nm.}, keywords = {Carrier-selective junctions, numerical simulations, pinholes, polysilicon on oxide, Tunneling}, pubstate = {forthcoming}, tppubtype = {article} } We investigate the transport mechanism of poly-Si-based carrier-selective junctions using the two-dimensional numerical semiconductor device simulations. The detailed transport model considers the charge carrier transport through the pinholes as well as tunneling through a very thin silicon oxide simultaneously. For the verification of the simulation model, the complete temperature dependent transfer length method is modeled and its results are verified with measurements of two different samples. By means of rigorous simulations, the influence of different pinhole geometrical and material parameters on junction resistivity are investigated and explained in detail. From the presented results, the fundamental understanding needed for optimizing the poly-Si-based carrier selective junction in respect to the main design parameters such as doping level in poly-Si, annealing time, silicon oxide thickness, and pinhole density is given. The detailed analysis shows the pinhole channel plays the most crucial role in the design of poly-Si-based carrier-selective junctions if the silicon oxide layer thickness is larger than 2 nm.
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M. Winter, D. Walter, D. Bredemeier, and J. Schmidt Light-induced lifetime degradation effects at elevated temperature in Czochralski-grown silicon beyond boron-oxygen-related degradation Journal Article Solar Energy Materials and Solar Cells 201 , 110060, (2019), ISSN: 0927-0248. Abstract | Links | BibTeX | Tags: boron-oxygen defect, Carrier lifetime, Czochralski-grown silicon, LeTID @article{Winter2019c,
title = {Light-induced lifetime degradation effects at elevated temperature in Czochralski-grown silicon beyond boron-oxygen-related degradation}, author = {M Winter and D Walter and D Bredemeier and J Schmidt}, doi = {10.1016/j.solmat.2019.110060}, issn = {0927-0248}, year = {2019}, date = {2019-10-01}, journal = {Solar Energy Materials and Solar Cells}, volume = {201}, pages = {110060}, abstract = {The effect of ‘Light and elevated Temperature Induced Degradation’ (LeTID) of the carrier lifetime is well known from multicrystalline silicon (mc-Si) wafers and solar cells. In this contribution, we perform a series of carrier lifetime measurements to examine, whether the same effect may also be observable in boron-doped Czochralski-grown silicon (Cz-Si). The Cz-Si samples of our study are illuminated (i) at room temperature, (ii) under standard regeneration conditions eliminating the boron-oxygen (BO) related defect (i.e. at 185 °C) and (iii) at a temperature of 80 °C, typical for the examination of the LeTID effect in mc-Si. We observe the typical decay of the carrier lifetime due to the activation of the BO-related defect. Beyond the BO degradation, applying standard solar cell processes, there is no indication for the activation of a second defect. On samples, whose surfaces are passivated by fired hydrogen-rich silicon nitride layers, an additional bulk lifetime degradation effect on a long timescale is observed in the Cz-Si material. However, defect generation rate and injection dependence of the lifetime suggest another defect type than the mc-Si-specific LeTID defect. We conclude that by applying processing steps that trigger LeTID in mc-Si, the same defect does not occur in the Cz-Si samples examined in this study. On a long timescale, however, a hitherto unknown type of defect is activated, which is different from the mc-Si-specific LeTID defect. A careful differentiation between the various kinds of recombination centres which may form during illumination at elevated temperatures is hence of utmost importance.}, keywords = {boron-oxygen defect, Carrier lifetime, Czochralski-grown silicon, LeTID}, pubstate = {published}, tppubtype = {article} } The effect of ‘Light and elevated Temperature Induced Degradation’ (LeTID) of the carrier lifetime is well known from multicrystalline silicon (mc-Si) wafers and solar cells. In this contribution, we perform a series of carrier lifetime measurements to examine, whether the same effect may also be observable in boron-doped Czochralski-grown silicon (Cz-Si). The Cz-Si samples of our study are illuminated (i) at room temperature, (ii) under standard regeneration conditions eliminating the boron-oxygen (BO) related defect (i.e. at 185 °C) and (iii) at a temperature of 80 °C, typical for the examination of the LeTID effect in mc-Si. We observe the typical decay of the carrier lifetime due to the activation of the BO-related defect. Beyond the BO degradation, applying standard solar cell processes, there is no indication for the activation of a second defect. On samples, whose surfaces are passivated by fired hydrogen-rich silicon nitride layers, an additional bulk lifetime degradation effect on a long timescale is observed in the Cz-Si material. However, defect generation rate and injection dependence of the lifetime suggest another defect type than the mc-Si-specific LeTID defect. We conclude that by applying processing steps that trigger LeTID in mc-Si, the same defect does not occur in the Cz-Si samples examined in this study. On a long timescale, however, a hitherto unknown type of defect is activated, which is different from the mc-Si-specific LeTID defect. A careful differentiation between the various kinds of recombination centres which may form during illumination at elevated temperatures is hence of utmost importance.
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D. Büchner, and O. Mercker OptDienE - Optionen zum netzdienlichen Betrieb von Einzelraumfeuerstätten Presentation Leipzig, Germany, 18.09.2019, (8. Statuskonferenz Energetische Biomassenutzung). Abstract | BibTeX | Tags: Netzdienlichkeit @misc{Büchner2019,
title = {OptDienE - Optionen zum netzdienlichen Betrieb von Einzelraumfeuerstätten}, author = {D Büchner and O Mercker}, year = {2019}, date = {2019-09-18}, address = {Leipzig, Germany}, abstract = {Die Transformation der Energieversorgung im Zuge der Energiewende ist durch einige Megatrends gekennzeichnet: (i) eine Dezentralisierung der Energiebereitstellung, (ii) eine Digitalisierung aller Lebensbereiche, (iii) eine dominierende Rolle von Solar- und Windenergie im Stromsektor und, damit einhergehend, (iv) eine hohe Volatilität der Erzeugung und (v) eine zunehmende Verschrän-kung der Energienutzungsbereiche: Strom, Wärme und Mobilität.Die im deutschen Markt derzeit installierten Einzelraumfeuerungen (ERF) haben zusammen eine thermische Kapazität von mindestens 80 bis 90 GW. Würde ein Teil dieser Feuerungen als multi-valente Anlagen in Kombination mit Wärmepumpen betrieben und dabei zumindest teilweise sys-temdienlich eingesetzt werden, könnten sie Strombedarfsspitzen von bis zu 30 GWel vermeiden. Bei einer wachsenden Bedeutung von Wärmepumpen und Elektromobilität könnte der zeitlich gesteuerte Einsatz von Biomasse-ERF zu einer maßgeblichen Entlastung des Stromnetzes und der Strombereitstellungskapazitäten in Hochlastzeiträumen mit geringer Stromeinspeisung aus Wind-kraft und PV-Anlagen beitragen.Das vorgestellte Forschungsvorhaben gliedert sich in den Schwerpunkt „SmartBiomassHeat“ des DBFZ ein.}, note = {8. Statuskonferenz Energetische Biomassenutzung}, keywords = {Netzdienlichkeit}, pubstate = {published}, tppubtype = {presentation} } Die Transformation der Energieversorgung im Zuge der Energiewende ist durch einige Megatrends gekennzeichnet: (i) eine Dezentralisierung der Energiebereitstellung, (ii) eine Digitalisierung aller Lebensbereiche, (iii) eine dominierende Rolle von Solar- und Windenergie im Stromsektor und, damit einhergehend, (iv) eine hohe Volatilität der Erzeugung und (v) eine zunehmende Verschrän-kung der Energienutzungsbereiche: Strom, Wärme und Mobilität.Die im deutschen Markt derzeit installierten Einzelraumfeuerungen (ERF) haben zusammen eine thermische Kapazität von mindestens 80 bis 90 GW. Würde ein Teil dieser Feuerungen als multi-valente Anlagen in Kombination mit Wärmepumpen betrieben und dabei zumindest teilweise sys-temdienlich eingesetzt werden, könnten sie Strombedarfsspitzen von bis zu 30 GWel vermeiden. Bei einer wachsenden Bedeutung von Wärmepumpen und Elektromobilität könnte der zeitlich gesteuerte Einsatz von Biomasse-ERF zu einer maßgeblichen Entlastung des Stromnetzes und der Strombereitstellungskapazitäten in Hochlastzeiträumen mit geringer Stromeinspeisung aus Wind-kraft und PV-Anlagen beitragen.Das vorgestellte Forschungsvorhaben gliedert sich in den Schwerpunkt „SmartBiomassHeat“ des DBFZ ein.
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D. C. Walter, D. Bredemeier, R. Falster, V. V. Voronkov, and J. Schmidt Easy-to-apply methodology to measure the hydrogen concentration in boron-doped crystalline silicon Journal Article Solar Energy Materials and Solar Cells 200 , 109970, (2019), ISSN: 0927-0248. Abstract | Links | BibTeX | Tags: Boron-hydrogen-pairs, crystalline silicon, Hydrogen @article{Walter2019c,
title = {Easy-to-apply methodology to measure the hydrogen concentration in boron-doped crystalline silicon}, author = {D C Walter and D Bredemeier and R Falster and V V Voronkov and J Schmidt}, doi = {10.1016/j.solmat.2019.109970}, issn = {0927-0248}, year = {2019}, date = {2019-09-15}, journal = {Solar Energy Materials and Solar Cells}, volume = {200}, pages = {109970}, abstract = {Hydrogen is a highly relevant impurity in crystalline silicon associated with a variety of effects particularly important in solar cell technology such as defect and surface passivation. It has been the subject of countless studies. Much of this however relies to a certain degree on speculation due to limitations in hydrogen measurement capability, making a direct quantitative correlation of these phenomena with the hydrogen content largely impossible so far. In this contribution, we apply recent advances in the understanding of hydrogen introduction and behaviour in silicon - in particular the conversion of quenched in dimeric hydrogen to boron hydrogen pairs (BH) - and introduce an easy-to-apply methodology to determine quantitatively the hydrogen concentration in bulk boron-doped silicon. The technique involves the measurement and analysis of changes to the bulk resistivity, as recorded by contactless eddy-current measurements, due to the formation of BH pairs during annealing at temperatures between 140 and 180 °C. To demonstrate the method, we apply it to boron-doped float-zone silicon wafers with SiNx:H coatings of different compositions, introducing different total hydrogen concentrations between 5 × 1014 and 1.3 × 1015 cm−3 into the silicon bulk during a fast-firing step. Without firing, the hydrogen content is below the detection limit of 3 × 1014 cm−3 for the 1 Ω cm test sample used.}, keywords = {Boron-hydrogen-pairs, crystalline silicon, Hydrogen}, pubstate = {published}, tppubtype = {article} } Hydrogen is a highly relevant impurity in crystalline silicon associated with a variety of effects particularly important in solar cell technology such as defect and surface passivation. It has been the subject of countless studies. Much of this however relies to a certain degree on speculation due to limitations in hydrogen measurement capability, making a direct quantitative correlation of these phenomena with the hydrogen content largely impossible so far. In this contribution, we apply recent advances in the understanding of hydrogen introduction and behaviour in silicon - in particular the conversion of quenched in dimeric hydrogen to boron hydrogen pairs (BH) - and introduce an easy-to-apply methodology to determine quantitatively the hydrogen concentration in bulk boron-doped silicon. The technique involves the measurement and analysis of changes to the bulk resistivity, as recorded by contactless eddy-current measurements, due to the formation of BH pairs during annealing at temperatures between 140 and 180 °C. To demonstrate the method, we apply it to boron-doped float-zone silicon wafers with SiNx:H coatings of different compositions, introducing different total hydrogen concentrations between 5 × 1014 and 1.3 × 1015 cm−3 into the silicon bulk during a fast-firing step. Without firing, the hydrogen content is below the detection limit of 3 × 1014 cm−3 for the 1 Ω cm test sample used.
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S. Schäfer, F. Haase, C. Hollemann, J. Hensen, J. Krügener, R. Brendel, and R. Peibst 26%-efficient and 2 cm narrow interdigitated back contact silicon solar cells with passivated slits on two edges Journal Article Solar Energy Materials and Solar Cells 200 , 110021, (2019), ISSN: 0927-0248. Abstract | Links | BibTeX | Tags: Back-contact solar cell, Edge loss, passivating contacts, perimeter recombination @article{Schäfer2019c,
title = {26%-efficient and 2 cm narrow interdigitated back contact silicon solar cells with passivated slits on two edges}, author = {S Schäfer and F Haase and C Hollemann and J Hensen and J Krügener and R Brendel and R Peibst}, doi = {10.1016/j.solmat.2019.110021}, issn = {0927-0248}, year = {2019}, date = {2019-09-15}, journal = {Solar Energy Materials and Solar Cells}, volume = {200}, pages = {110021}, abstract = {Perimeter recombination is a relevant loss mechanism, in particular for cells with a large perimeter-to-area ratio and with poorly passivated edges, e.g., cut or cleaved solar cells for shingled modules. We experimentally demonstrate that cut edges can be well passivated during front-end processing. The resulting cells have an efficiency of 26%. The designated cell area of our lab-type highly efficient cells is smaller than the total area of the wafer. This causes recombination losses in the masked perimeter region. We separate the active cell area from the wafer on two sides of the cell by slits to reduce the transport of carriers into the perimeter region. We apply a diffusion model to describe impact of the slits on the perimeter recombination. The slits have an effective surface recombination velocity of down to 9 cm/s, depending on the resistivity of the base. For a base resistivity of 80 Ωcm, the average cell efficiency increases by 0.7 %abs as compared to embedded cells and by 2.3 %abs as compared to laser-cut cells due to the passivated slits.}, keywords = {Back-contact solar cell, Edge loss, passivating contacts, perimeter recombination}, pubstate = {published}, tppubtype = {article} } Perimeter recombination is a relevant loss mechanism, in particular for cells with a large perimeter-to-area ratio and with poorly passivated edges, e.g., cut or cleaved solar cells for shingled modules. We experimentally demonstrate that cut edges can be well passivated during front-end processing. The resulting cells have an efficiency of 26%. The designated cell area of our lab-type highly efficient cells is smaller than the total area of the wafer. This causes recombination losses in the masked perimeter region. We separate the active cell area from the wafer on two sides of the cell by slits to reduce the transport of carriers into the perimeter region. We apply a diffusion model to describe impact of the slits on the perimeter recombination. The slits have an effective surface recombination velocity of down to 9 cm/s, depending on the resistivity of the base. For a base resistivity of 80 Ωcm, the average cell efficiency increases by 0.7 %abs as compared to embedded cells and by 2.3 %abs as compared to laser-cut cells due to the passivated slits.
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H. Schulte-Huxel, S. Blankemeyer, A. Morlier, R. Brendel, and M. Köntges Interconnect-shingling: Maximizing the active module area with conventional module processes Journal Article Solar Energy Materials and Solar Cells 200 , 109991, (2019), ISSN: 0927-0248. Abstract | Links | BibTeX | Tags: High efficiency PV modules, module integration, Shingled interconnection, Solar cell interconnection @article{Schulte-Huxel2019b,
title = {Interconnect-shingling: Maximizing the active module area with conventional module processes}, author = {H Schulte-Huxel and S Blankemeyer and A Morlier and R Brendel and M Köntges}, doi = {10.1016/j.solmat.2019.109991}, issn = {0927-0248}, year = {2019}, date = {2019-09-15}, journal = {Solar Energy Materials and Solar Cells}, volume = {200}, pages = {109991}, abstract = {We present a module fabrication process enabling gap-free interconnection of c-Si solar cells using solder-based interconnection technology with ribbons or wires. The interconnect-shingling process increases the module efficiency by avoiding the gaps between the solar cells. The process is applicable to bifacial cells and uses well-proven interconnection technologies. In contrast to previous adhesive-based shingled modules, the current transport is supported by interconnects, thus reducing the silver consumption for the cells’ metallization and avoiding cell overlap. We lay down the cells on structured encapsulant layers to reduce mechanical stress at the cell edges during lamination. Alternatively, the lamination process can be adapted to allow the encapsulant to reflow. This also results in a low pressure at sensitive cell parts. Both approaches avoid crack formation. We demonstrate the interconnect-shingling process with a proof-of-concept module having a aperture area efficiency of 22.1%. Applying 200 thermal cycles does not cause any crack formation.}, keywords = {High efficiency PV modules, module integration, Shingled interconnection, Solar cell interconnection}, pubstate = {published}, tppubtype = {article} } We present a module fabrication process enabling gap-free interconnection of c-Si solar cells using solder-based interconnection technology with ribbons or wires. The interconnect-shingling process increases the module efficiency by avoiding the gaps between the solar cells. The process is applicable to bifacial cells and uses well-proven interconnection technologies. In contrast to previous adhesive-based shingled modules, the current transport is supported by interconnects, thus reducing the silver consumption for the cells’ metallization and avoiding cell overlap. We lay down the cells on structured encapsulant layers to reduce mechanical stress at the cell edges during lamination. Alternatively, the lamination process can be adapted to allow the encapsulant to reflow. This also results in a low pressure at sensitive cell parts. Both approaches avoid crack formation. We demonstrate the interconnect-shingling process with a proof-of-concept module having a aperture area efficiency of 22.1%. Applying 200 thermal cycles does not cause any crack formation.
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T. Ohrdes, E. Schneider, M. Knoop, O. Bast, and V. Spielmann Wind-Solar-Wärmepumpen-Quartier – Dynamische Modellierung und messtechnische Evaluation der Strom- und Wärmeversorgung im Quartier Presentation Berlin, Germany, 13.09.2019, (5. Dialogplattform Power-to-Heat). @misc{Ohrdes2019b,
title = {Wind-Solar-Wärmepumpen-Quartier – Dynamische Modellierung und messtechnische Evaluation der Strom- und Wärmeversorgung im Quartier}, author = {T Ohrdes and E Schneider and M Knoop and O Bast and V Spielmann}, year = {2019}, date = {2019-09-13}, address = {Berlin, Germany}, note = {5. Dialogplattform Power-to-Heat}, keywords = {Quartier}, pubstate = {published}, tppubtype = {presentation} } |
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R. Peibst, F. Haase, H. Schulte-Huxel, S. Blankemeyer, M. Köntges, C. Hollemann, R. Brendel, G. Wetzel, J. Krügener, H-J. Nonnenmacher, H. Mehlich, M. Stein, R. Wecker, A. Schiessl, J. Süss, F. Metzger, C. Schreibmüller, K. Ding, A. Lambertz, W. Duan, A. Mikosch, B. Pieters, B. Stannowski, and L. Korte Efficient Si Photovoltaics for Electrically Powered Utility Vehicles – STREET Presentation Marseille, France, 13.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: VIPV @misc{Peibst2019d,
title = {Efficient Si Photovoltaics for Electrically Powered Utility Vehicles – STREET}, author = {R Peibst and F Haase and H Schulte-Huxel and S Blankemeyer and M Köntges and C Hollemann and R Brendel and G Wetzel and J Krügener and H-J Nonnenmacher and H Mehlich and M Stein and R Wecker and A Schiessl and J Süss and F Metzger and C Schreibmüller and K Ding and A Lambertz and W Duan and A Mikosch and B Pieters and B Stannowski and L Korte}, year = {2019}, date = {2019-09-13}, address = {Marseille, France}, abstract = { The emerging approach to integrate photovoltaics into electrically driven vehicles (VIPV, vehicle integrated PV) can contribute to the urgent reduction of the emission of greenhouse- and other harmful gases, and help to reduce peak loads for the electric grid and provide balance energy. The current challenge is to demonstrate experimentally that these contributions can be as significant as projected [1], and that VIPV can be economically viable. To achieve this objective, a2-solar, Continental, HZB, ISFH, JÜLICH, MBE, Meyer-Burger and StreetScooter – join their expertise in the “Street” project. The specific innovations of Street are: (0) A focus on light commercial vehicles with an appropriate driving pattern and relaxed requirements on aesthetics such as curvature of the PV modules, (i) improve two high-efficiency c-Si technologies – double-side contacted silicon heterojunction (SHJ) cells and polysilicon on oxide (POLO)-IBC cells and adapt them to VIPV, (ii) evaluate transparent n-type doped nanocrystalline Si:O electron collecting junctions and Indium Tungsten Oxide based TCOs for the first and integrated bypass diodes (to maximize energy yield under dynamic partial shading) by the latter cell technology, (iii) apply the mechanical robust Smart-Wire Cell interconnection technology for both cell concepts, (iv) develop lightweight and durable VIPV modules, (v) develop a very fast maximum power point tracker and a buck-boost DC/DC converter, (vii) integrate these components into the innovative light commercial vehicle “WORK L” and perform test drives with representative drive patterns, and (viii) develop prediction models for the energy yield and corresponding range extension on timescales between one day and one year. We target a solar coverage of 20% for the energy used for driving.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {VIPV}, pubstate = {published}, tppubtype = {presentation} } The emerging approach to integrate photovoltaics into electrically driven vehicles (VIPV, vehicle integrated PV) can contribute to the urgent reduction of the emission of greenhouse- and other harmful gases, and help to reduce peak loads for the electric grid and provide balance energy. The current challenge is to demonstrate experimentally that these contributions can be as significant as projected [1], and that VIPV can be economically viable. To achieve this objective, a2-solar, Continental, HZB, ISFH, JÜLICH, MBE, Meyer-Burger and StreetScooter – join their expertise in the “Street” project. The specific innovations of Street are: (0) A focus on light commercial vehicles with an appropriate driving pattern and relaxed requirements on aesthetics such as curvature of the PV modules, (i) improve two high-efficiency c-Si technologies – double-side contacted silicon heterojunction (SHJ) cells and polysilicon on oxide (POLO)-IBC cells and adapt them to VIPV, (ii) evaluate transparent n-type doped nanocrystalline Si:O electron collecting junctions and Indium Tungsten Oxide based TCOs for the first and integrated bypass diodes (to maximize energy yield under dynamic partial shading) by the latter cell technology, (iii) apply the mechanical robust Smart-Wire Cell interconnection technology for both cell concepts, (iv) develop lightweight and durable VIPV modules, (v) develop a very fast maximum power point tracker and a buck-boost DC/DC converter, (vii) integrate these components into the innovative light commercial vehicle “WORK L” and perform test drives with representative drive patterns, and (viii) develop prediction models for the energy yield and corresponding range extension on timescales between one day and one year. We target a solar coverage of 20% for the energy used for driving.
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M-U. Halbich, R. Sauer-Stieglitz, W. Lövenich, and J. Schmidt Improving Organic-Silicon Heterojunction Solar Cells through the Admixture of Sorbitol to PEDOT:PSS Presentation Marseille, France, 11.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: PEDOT:PSS @misc{Halbich2019b,
title = { Improving Organic-Silicon Heterojunction Solar Cells through the Admixture of Sorbitol to PEDOT:PSS}, author = {M-U Halbich and R Sauer-Stieglitz and W Lövenich and J Schmidt}, year = {2019}, date = {2019-09-11}, address = {Marseille, France}, abstract = {We examine the impact of Sorbitol admixture on the hole conductive polymer PEDOT:PSS[poly(3,4ethylenedioxythiophene):poly(styrenesulfonate)] in combination with a variation of the annealing duration. As demonstrated in a previous publication, the admixture of Sorbitol to the PEDOT:PSS dispersion is improving the transparency of the organic layer and is also improving the surface passivation. On the other hand, the contact resistance on the silicon surface tends to increase by admixture of Sorbitol. In this study, we fabricate solar cells where the PEDOT:PSS layer is used as a hole-selective contact at the cell rear (so-called ‘BackPEDOT’ solar cells). The electron-selective front is conventionally processed by means of phosphorus diffusion. The passivation of the silicon surface with PEDOT:PSS:Sorbitol shows an improvement in the passivation quality and the solar cells show an increasing open-circuit voltage Voc by increasing the annealing duration from the previously routinely applied 10 min to 60 min. The short-circuit current density Jsc of the fabricated solar cells remains unchanged for all investigated annealing durations. Importantly, the series resistance Rs (and hence the contact resistance) of the fabricated BackPEDOT solar cells show a minimum for annealing durations between 45 and 90 min. As a consequence, increasing the annealing duration led to an increased maximum energy conversion efficiency of 20.6% at one sun.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {PEDOT:PSS}, pubstate = {published}, tppubtype = {presentation} } We examine the impact of Sorbitol admixture on the hole conductive polymer PEDOT:PSS[poly(3,4ethylenedioxythiophene):poly(styrenesulfonate)] in combination with a variation of the annealing duration. As demonstrated in a previous publication, the admixture of Sorbitol to the PEDOT:PSS dispersion is improving the transparency of the organic layer and is also improving the surface passivation. On the other hand, the contact resistance on the silicon surface tends to increase by admixture of Sorbitol. In this study, we fabricate solar cells where the PEDOT:PSS layer is used as a hole-selective contact at the cell rear (so-called ‘BackPEDOT’ solar cells). The electron-selective front is conventionally processed by means of phosphorus diffusion. The passivation of the silicon surface with PEDOT:PSS:Sorbitol shows an improvement in the passivation quality and the solar cells show an increasing open-circuit voltage Voc by increasing the annealing duration from the previously routinely applied 10 min to 60 min. The short-circuit current density Jsc of the fabricated solar cells remains unchanged for all investigated annealing durations. Importantly, the series resistance Rs (and hence the contact resistance) of the fabricated BackPEDOT solar cells show a minimum for annealing durations between 45 and 90 min. As a consequence, increasing the annealing duration led to an increased maximum energy conversion efficiency of 20.6% at one sun.
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G. Mathiak, W. Herrmann, F. Reil, A. Morlier, S. Großer, M. Pander, S. Schindler, M. Turek, and M. Ebert Durable PV Modules - Requirements for the Module Design and Aspects of Reliability Testing Techniques Presentation Marseille, France, 10.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: EVA, Long sequential testing, Module Reliability, PERC cell, Polyolefin, Qualification and Testing @misc{Mathiak2019,
title = {Durable PV Modules - Requirements for the Module Design and Aspects of Reliability Testing Techniques}, author = {G Mathiak and W Herrmann and F Reil and A Morlier and S Großer and M Pander and S Schindler and M Turek and M Ebert}, year = {2019}, date = {2019-09-10}, address = {Marseille, France}, abstract = {The aim of this work was to develop a PV module design with current components that is resistant to degradation mechanisms without increasing costs. A glass–foil module design with a 4 mm thick front glass with antireflective coating was chosen. The encapsulation material was varied (polyolefin and EVA from two manufacturers). The two test module series have different PERC cell types (multicrystalline with three busbars and monocrystalline with five busbars). We have developed a long sequential test sequence to evaluate the reliability of the modules according to the selected degradation modes. The test sequence included damp heat (3000 h), thermal cycling (200x) and UV light exposure (60 kWh/m²) with hail and mechanical stress testing. The performance of the polyolefin modules was better after the long test sequence. The second module series was better due to the better cells.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {EVA, Long sequential testing, Module Reliability, PERC cell, Polyolefin, Qualification and Testing}, pubstate = {published}, tppubtype = {presentation} } The aim of this work was to develop a PV module design with current components that is resistant to degradation mechanisms without increasing costs. A glass–foil module design with a 4 mm thick front glass with antireflective coating was chosen. The encapsulation material was varied (polyolefin and EVA from two manufacturers). The two test module series have different PERC cell types (multicrystalline with three busbars and monocrystalline with five busbars). We have developed a long sequential test sequence to evaluate the reliability of the modules according to the selected degradation modes. The test sequence included damp heat (3000 h), thermal cycling (200x) and UV light exposure (60 kWh/m²) with hail and mechanical stress testing. The performance of the polyolefin modules was better after the long test sequence. The second module series was better due to the better cells.
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R. Peibst, C. Kruse, S. Schäfer, V. Mertens, T. Dullweber, and R. Brendel For none, one or two polarities – how do POLO junctions fit best into industrial Si solar cells? Presentation Marseille, France, 10.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: POLO @misc{Peibst2019c,
title = {For none, one or two polarities – how do POLO junctions fit best into industrial Si solar cells?}, author = {R Peibst and C Kruse and S Schäfer and V Mertens and T Dullweber and R Brendel}, year = {2019}, date = {2019-09-10}, address = {Marseille, France}, abstract = {The implementation of passivating contacts into industrial solar cells is an important subject of ongoing world-wide research. The evolutionary improvement of the PERC technology is a fast moving target for alternative approaches and thus any increase in process complexity has to be counterbalanced by a significant gain in efficiency. However, the difference in the efficiency potential (as compared to the projection for PERC) is moderate for most alternative cell concepts such as those with passivating contacts. This is in particular true if passivating contacts are applied only for one polarity. One possibility to address the “leaky bucket problem” on double-side contacted structures without the usage of a TCO is applying poly-Si on both polarities while the front side is structured (Boss). Here we introduce a back-junction Boss structure and an elegant process flow to realize this structure using Low Pressure Chemical Vapor Deposition (LPCVD). The process makes a strength out of the original weakness of LPCVD being a double-sided deposition. It also allows for an integration of bypass diodes within the cell. The successful experimental demonstration of the most critical process steps is reported. Cell results will be reported at the conference. We also report a systematic device simulation study, showing that the Boss structure has a significantly higher efficiency potential than projected with an evolutionary improvement of the PERC structure, as well as that for “PERC-like” structures with POLO junctions for either exclusively electron or hole collection. We also simulate a “PERT-like” structure with n+-type POLO on the rear (TOPCon, monoPoly, PERPoly, …) for comparison. At the conference, we intend to present our own works in the broad context of the work of other groups in this active research field.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {POLO}, pubstate = {published}, tppubtype = {presentation} } The implementation of passivating contacts into industrial solar cells is an important subject of ongoing world-wide research. The evolutionary improvement of the PERC technology is a fast moving target for alternative approaches and thus any increase in process complexity has to be counterbalanced by a significant gain in efficiency. However, the difference in the efficiency potential (as compared to the projection for PERC) is moderate for most alternative cell concepts such as those with passivating contacts. This is in particular true if passivating contacts are applied only for one polarity. One possibility to address the “leaky bucket problem” on double-side contacted structures without the usage of a TCO is applying poly-Si on both polarities while the front side is structured (Boss). Here we introduce a back-junction Boss structure and an elegant process flow to realize this structure using Low Pressure Chemical Vapor Deposition (LPCVD). The process makes a strength out of the original weakness of LPCVD being a double-sided deposition. It also allows for an integration of bypass diodes within the cell. The successful experimental demonstration of the most critical process steps is reported. Cell results will be reported at the conference. We also report a systematic device simulation study, showing that the Boss structure has a significantly higher efficiency potential than projected with an evolutionary improvement of the PERC structure, as well as that for “PERC-like” structures with POLO junctions for either exclusively electron or hole collection. We also simulate a “PERT-like” structure with n+-type POLO on the rear (TOPCon, monoPoly, PERPoly, …) for comparison. At the conference, we intend to present our own works in the broad context of the work of other groups in this active research field.
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Y. Larionova, H. Schulte-Huxel, B. Min, S. Hartmann, M. Turcu, T. Kluge, H. Mehlich, R. Brendel, and R. Peibst Screen Printed Double-Side Contacted POLO-Cells with Ultra-Thin Poly-Si Layers and Different Transparent Conductive Oxides Presentation Marseille, France, 10.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: passivating contact, Polycrystalline Silicon (Si), silicon solar cells, Transparent Conducting Oxides (TCO) @misc{Larionova2019,
title = {Screen Printed Double-Side Contacted POLO-Cells with Ultra-Thin Poly-Si Layers and Different Transparent Conductive Oxides}, author = {Y Larionova and H Schulte-Huxel and B Min and S Hartmann and M Turcu and T Kluge and H Mehlich and R Brendel and R Peibst}, year = {2019}, date = {2019-09-10}, address = {Marseille, France}, abstract = {In this work we demonstrate various measures to improve the efficiency of large-area screen-printed double-side contacted POLO-cells with different transparent conductive oxides (TCO). We experimentally increase the short-circuit current density Jsc up to 0.6 mA/cm2 by reducing the thickness of poly-Si from 25 nm to 10 nm due to the reduction of the parasitic absorption in the poly-Si layer at the textured cell front side. An implemented hydrogenation step with AlxOy and post-deposition anneal of TCO enable remarkably high implied open-circuit voltage Voc,impl values on n-type cell precursors after the sputtering process. All cell precursors show Voc,impl of up to 740 mV independent of the poly-Si thickness. We find an improvement of the open-circuit voltage Voc of the final cells of up to 728 mV, a cell efficiency of up to 22.3% with indium tin oxide, and a cell efficiency of 21.6% with an aluminum-doped zinc oxide on top or the n+-type POLO layer.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {passivating contact, Polycrystalline Silicon (Si), silicon solar cells, Transparent Conducting Oxides (TCO)}, pubstate = {published}, tppubtype = {presentation} } In this work we demonstrate various measures to improve the efficiency of large-area screen-printed double-side contacted POLO-cells with different transparent conductive oxides (TCO). We experimentally increase the short-circuit current density Jsc up to 0.6 mA/cm2 by reducing the thickness of poly-Si from 25 nm to 10 nm due to the reduction of the parasitic absorption in the poly-Si layer at the textured cell front side. An implemented hydrogenation step with AlxOy and post-deposition anneal of TCO enable remarkably high implied open-circuit voltage Voc,impl values on n-type cell precursors after the sputtering process. All cell precursors show Voc,impl of up to 740 mV independent of the poly-Si thickness. We find an improvement of the open-circuit voltage Voc of the final cells of up to 728 mV, a cell efficiency of up to 22.3% with indium tin oxide, and a cell efficiency of 21.6% with an aluminum-doped zinc oxide on top or the n+-type POLO layer.
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S. Bordihn, B. Min, R. Peibst, and R. Brendel Modelling of Passivation and Resistance of n-Type poly-Si Layers by Trained Artificial Neural Networks Presentation Marseille, France, 10.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: Artificial Neural Network, Modelling / Modeling, Polycrystalline Silicon (Si), surface passivation @misc{Bordihn2019,
title = {Modelling of Passivation and Resistance of n-Type poly-Si Layers by Trained Artificial Neural Networks}, author = {S Bordihn and B Min and R Peibst and R Brendel}, year = {2019}, date = {2019-09-10}, address = {Marseille, France}, abstract = {This paper studies the passivation quality and sheet resistance of n-type poly-Si on oxide (POLO) layers that we prepare at various post-deposition annealing temperatures. The n-type poly-Si layers are 50 nm-thin and grown on textured and planar Cz Si substrates. The samples are annealed from 880 °C to 1000 °C to transform the amorphous Si to poly-crystalline Si. The surface passivation quality is evaluated after the aforementioned anneal step, after an additional hydrogenation step (induced by Al2O3 capping layers and subsequent low temperature anneal), and after firing at 840 °C peak temperature. The optimal surface passivation quality is found for annealing at 960 °C and hydrogenation, resulting in iVoc-values of 710 mV. The hydrogenation step improves the iVoc by ~20 mV depending on the post-deposition annealing temperature. We find that surface passivation and sheet resistance of the poly-Si layers increased with increasing anneal temperature up to 960 °C and starts to decline above 980 °C. This trend is found to correlate with the amount of in-diffused dopants that depends also on the annealing temperature. We show that artificial neural network based model can serve as a fast tool for predicting layer properties that depend on multiple process parameters. The quality of the modelling is the same as that using the Design of Experiment method.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {Artificial Neural Network, Modelling / Modeling, Polycrystalline Silicon (Si), surface passivation}, pubstate = {published}, tppubtype = {presentation} } This paper studies the passivation quality and sheet resistance of n-type poly-Si on oxide (POLO) layers that we prepare at various post-deposition annealing temperatures. The n-type poly-Si layers are 50 nm-thin and grown on textured and planar Cz Si substrates. The samples are annealed from 880 °C to 1000 °C to transform the amorphous Si to poly-crystalline Si. The surface passivation quality is evaluated after the aforementioned anneal step, after an additional hydrogenation step (induced by Al2O3 capping layers and subsequent low temperature anneal), and after firing at 840 °C peak temperature. The optimal surface passivation quality is found for annealing at 960 °C and hydrogenation, resulting in iVoc-values of 710 mV. The hydrogenation step improves the iVoc by ~20 mV depending on the post-deposition annealing temperature. We find that surface passivation and sheet resistance of the poly-Si layers increased with increasing anneal temperature up to 960 °C and starts to decline above 980 °C. This trend is found to correlate with the amount of in-diffused dopants that depends also on the annealing temperature. We show that artificial neural network based model can serve as a fast tool for predicting layer properties that depend on multiple process parameters. The quality of the modelling is the same as that using the Design of Experiment method.
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M. R. Vogt, R. Witteck, T. Gewohn, H. Schulte-Huxel, C. Schinke, M. Köntges, K. Bothe, and R. Brendel Boosting PV Module Efficiency Beyond the Efficiency of Its Solar Cells – A Raytracing Study with Daidalos Now Available to the Scientific Community Presentation Marseille, France, 10.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: Antireflection Coating, module integration, Optical losses, PV Module, ray tracing, Simulation @misc{Vogt2019b,
title = {Boosting PV Module Efficiency Beyond the Efficiency of Its Solar Cells – A Raytracing Study with Daidalos Now Available to the Scientific Community}, author = {M R Vogt and R Witteck and T Gewohn and H Schulte-Huxel and C Schinke and M Köntges and K Bothe and R Brendel}, year = {2019}, date = {2019-09-10}, address = {Marseille, France}, abstract = {Today, the PV module energy conversion efficiency is below the efficiency of the cells prior to module integration. Using optical ray tracing simulations, we show how to increase module efficiencies beyond the efficiency of the solar cells. To achieve this we follow two basic principles: First, we minimize optical losses of the module components by minimizing the absorption in the glass and the encapsulation as well as by introducing multilayer glass ARC coatings that reduce the surface reflection. Second, we exploit the internal reflection at the glass-air interface by using light guiding structures in the cell gaps and as cell connects. This improves the light trapping by reducing the cell front side reflection losses. In our specific example presented in this work, the optimization leads to a module efficiency of 20.9%, which is a 0.1%abs above that of the non-encapsulated cells with an efficiency of 20.8%.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {Antireflection Coating, module integration, Optical losses, PV Module, ray tracing, Simulation}, pubstate = {published}, tppubtype = {presentation} } Today, the PV module energy conversion efficiency is below the efficiency of the cells prior to module integration. Using optical ray tracing simulations, we show how to increase module efficiencies beyond the efficiency of the solar cells. To achieve this we follow two basic principles: First, we minimize optical losses of the module components by minimizing the absorption in the glass and the encapsulation as well as by introducing multilayer glass ARC coatings that reduce the surface reflection. Second, we exploit the internal reflection at the glass-air interface by using light guiding structures in the cell gaps and as cell connects. This improves the light trapping by reducing the cell front side reflection losses. In our specific example presented in this work, the optimization leads to a module efficiency of 20.9%, which is a 0.1%abs above that of the non-encapsulated cells with an efficiency of 20.8%.
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J. Schmidt, D. Bredemeier, and D. C. Walter On the Defect Physics Behind Light and Elevated Temperature-Induced Degradation (LeTID) of Multicrystalline Silicon Solar Cells Journal Article Forthcoming IEEE Journal of Photovoltaics Forthcoming. Abstract | Links | BibTeX | Tags: defects, Degradation, Hydrogen, metallic impurity, multicrystalline silicon (mc-Si), silicon, Solar Cells @article{Schmidt2019d,
title = {On the Defect Physics Behind Light and Elevated Temperature-Induced Degradation (LeTID) of Multicrystalline Silicon Solar Cells}, author = {J Schmidt and D Bredemeier and D C Walter}, doi = {10.1109/JPHOTOV.2019.2937223}, year = {2019}, date = {2019-09-09}, journal = {IEEE Journal of Photovoltaics}, abstract = {State-of-the-art solar cells with passivated surfaces fabricated on block-cast multicrystalline silicon (mc-Si) wafers show a pronounced degradation in efficiency under illumination at elevated temperature, as it typically occurs during operation in a solar module. This effect, frequently named `Light and elevated Temperature-Induced Degradation' (LeTID), has been attributed to the activation of a specific, hitherto unrevealed bulk defect in mc-Si. Recent experimental results of several labs have indicated that hydrogen is somehow involved in the responsible defect physics, without however providing any direct evidence so far. In this article, we present experimental data unambiguously showing a direct positive correlation of the extent of LeTID with the hydrogen content introduced into the silicon bulk during firing of the silicon wafers coated with hydrogen-rich silicon nitride (SiN$_rm x$:H) layers. Additional experiments including the pronounced impact of phosphorus gettering on the LeTID extent and the dependence of the degradation and regeneration on the wafer thickness support the involvement of a second species, with most indications pointing towards a metallic impurity. Several approaches of completely avoiding the instability in mc-Si solar cells are derived from the presented defect model, including 1) tuning of the SiN$_rm x$:H layer properties to minimize the in-diffusion of hydrogen into the wafer and 2) the thinning of the mc-Si wafer, improving the getterability of the metal impurity component toward the surfaces.}, keywords = {defects, Degradation, Hydrogen, metallic impurity, multicrystalline silicon (mc-Si), silicon, Solar Cells}, pubstate = {forthcoming}, tppubtype = {article} } State-of-the-art solar cells with passivated surfaces fabricated on block-cast multicrystalline silicon (mc-Si) wafers show a pronounced degradation in efficiency under illumination at elevated temperature, as it typically occurs during operation in a solar module. This effect, frequently named `Light and elevated Temperature-Induced Degradation' (LeTID), has been attributed to the activation of a specific, hitherto unrevealed bulk defect in mc-Si. Recent experimental results of several labs have indicated that hydrogen is somehow involved in the responsible defect physics, without however providing any direct evidence so far. In this article, we present experimental data unambiguously showing a direct positive correlation of the extent of LeTID with the hydrogen content introduced into the silicon bulk during firing of the silicon wafers coated with hydrogen-rich silicon nitride (SiN$_rm x$:H) layers. Additional experiments including the pronounced impact of phosphorus gettering on the LeTID extent and the dependence of the degradation and regeneration on the wafer thickness support the involvement of a second species, with most indications pointing towards a metallic impurity. Several approaches of completely avoiding the instability in mc-Si solar cells are derived from the presented defect model, including 1) tuning of the SiN$_rm x$:H layer properties to minimize the in-diffusion of hydrogen into the wafer and 2) the thinning of the mc-Si wafer, improving the getterability of the metal impurity component toward the surfaces.
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D. Bredemeier, D. C. Walter, and J. Schmidt Impact of Silicon Nitride Film Properties on Hydrogen In-Diffusion into Crystalline Silicon Presentation Marseille, France, 09.09.2019, (36th European Photovoltaic Solar Energy Conference and Exhibition). Abstract | BibTeX | Tags: diffusion, Hydrogen, Rapid thermal annealing, silicon nitride @misc{Bredemeier2019c,
title = {Impact of Silicon Nitride Film Properties on Hydrogen In-Diffusion into Crystalline Silicon}, author = {D Bredemeier and D C Walter and J Schmidt}, year = {2019}, date = {2019-09-09}, address = {Marseille, France}, abstract = {Hydrogen-rich silicon nitride films deposited on top of crystalline silicon wafers are a common source of hydrogen within solar cell production. Upon rapid thermal annealing (RTA), hydrogen bonds within the silicon nitride films dissociate and the hydrogen diffuses both into the environment as well as into the silicon bulk. Within this study, we investigate the impact of silicon nitride material properties on the amount of hydrogen introduced into the silicon bulk during RTA treatment. The measurements clearly show that the atomic density of the silicon nitride film has a pronounced impact on the hydrogen in-diffusion. Importantly, we find that the total hydrogen loss during RTA within the silicon nitride films is not correlated with the actual amount of hydrogen introduced into the silicon bulk.}, note = {36th European Photovoltaic Solar Energy Conference and Exhibition}, keywords = {diffusion, Hydrogen, Rapid thermal annealing, silicon nitride}, pubstate = {published}, tppubtype = {presentation} } Hydrogen-rich silicon nitride films deposited on top of crystalline silicon wafers are a common source of hydrogen within solar cell production. Upon rapid thermal annealing (RTA), hydrogen bonds within the silicon nitride films dissociate and the hydrogen diffuses both into the environment as well as into the silicon bulk. Within this study, we investigate the impact of silicon nitride material properties on the amount of hydrogen introduced into the silicon bulk during RTA treatment. The measurements clearly show that the atomic density of the silicon nitride film has a pronounced impact on the hydrogen in-diffusion. Importantly, we find that the total hydrogen loss during RTA within the silicon nitride films is not correlated with the actual amount of hydrogen introduced into the silicon bulk.
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L. Helmich, D. C. Walter, and J. Schmidt Direct Examination of the Deactivation of the Boron–Oxygen Center in Cz-Si Solar Cells Under Regeneration Conditions via Electroluminescence Journal Article Forthcoming IEEE Journal of Photovoltaics 1-5, Forthcoming, ISSN: 2156-3381. Abstract | Links | BibTeX | Tags: boron–oxygen defect, carrier injection, Czochralski-grown silicon, electroluminescence (EL), light-induced degradation (LID), passivated emitter and rear cells (PERCs), regeneration @article{Helmich2019b,
title = {Direct Examination of the Deactivation of the Boron–Oxygen Center in Cz-Si Solar Cells Under Regeneration Conditions via Electroluminescence}, author = {L Helmich and D C Walter and J Schmidt}, doi = {10.1109/JPHOTOV.2019.2926855}, issn = {2156-3381}, year = {2019}, date = {2019-09-02}, journal = {IEEE Journal of Photovoltaics}, pages = {1-5}, abstract = {We examine the regeneration kinetics of the boron–oxygen defect in boron-doped p-type Czochralski-grown silicon (Cz-Si) solar cells as a function of the excess carrier concentration Δn at the regeneration conditions, i.e., at elevated temperature (140 °C). To perform the regeneration, we apply different forward-bias voltages (V$_rm appl$) to solar cells in darkness and measure directly the emitted electroluminescence (EL) signal at different time steps during the regeneration of the cell. Measuring the EL signal emitted by the solar cell during regeneration, we are able to directly determine Δn during regeneration for each applied voltage. In addition to the EL signal, we measure the electric current flowing through the solar cell during the regeneration process. This current is proportional to the overall recombination rate in the cell and, hence, reflects the changing bulk recombination during the regeneration process. From the measured time-dependent cell current, we determine the deactivation rate constant R$_rm de$ of the boron–oxygen defect. Our experimental results unambiguously show that R$_rm de$ increases proportionally with Δn during the regeneration process.}, keywords = {boron–oxygen defect, carrier injection, Czochralski-grown silicon, electroluminescence (EL), light-induced degradation (LID), passivated emitter and rear cells (PERCs), regeneration}, pubstate = {forthcoming}, tppubtype = {article} } We examine the regeneration kinetics of the boron–oxygen defect in boron-doped p-type Czochralski-grown silicon (Cz-Si) solar cells as a function of the excess carrier concentration Δn at the regeneration conditions, i.e., at elevated temperature (140 °C). To perform the regeneration, we apply different forward-bias voltages (V$_rm appl$) to solar cells in darkness and measure directly the emitted electroluminescence (EL) signal at different time steps during the regeneration of the cell. Measuring the EL signal emitted by the solar cell during regeneration, we are able to directly determine Δn during regeneration for each applied voltage. In addition to the EL signal, we measure the electric current flowing through the solar cell during the regeneration process. This current is proportional to the overall recombination rate in the cell and, hence, reflects the changing bulk recombination during the regeneration process. From the measured time-dependent cell current, we determine the deactivation rate constant R$_rm de$ of the boron–oxygen defect. Our experimental results unambiguously show that R$_rm de$ increases proportionally with Δn during the regeneration process.
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K. Bothe, and D. Hinken Precise and accurate solar cell measurements at ISFH CalTeC Miscellaneous Photovoltaics International Volume 43, (2019). Abstract | BibTeX | Tags: calibration @misc{Bothe2019b,
title = {Precise and accurate solar cell measurements at ISFH CalTeC}, author = {K Bothe and D Hinken}, year = {2019}, date = {2019-09-01}, abstract = {This paper presents the calibration of solar cells, in accordance with the IEC 60904 standards, carried out at the solar cell calibration laboratory of the Calibration and Test Center (CalTeC) at the Institute of Solar Energy Research Hamelin (ISFH). For the calibration of a solar cell, the cell area, the spectral responsivity (SR) and the current–voltage (I–V) curve have to be determined. The I–V curve then yields the characteristic parameters, including the power conversion efficiency, fill factor, short-circuit current and opencircuit voltage. The required measurement facilities and contacting stages are explained in detail; in addition, the measurement procedures are introduced. The precision and accuracy of the resulting characteristic parameters and curves are demonstrated by recent intercomparisons between different international calibration laboratories.}, howpublished = {Photovoltaics International Volume 43}, keywords = {calibration}, pubstate = {published}, tppubtype = {misc} } This paper presents the calibration of solar cells, in accordance with the IEC 60904 standards, carried out at the solar cell calibration laboratory of the Calibration and Test Center (CalTeC) at the Institute of Solar Energy Research Hamelin (ISFH). For the calibration of a solar cell, the cell area, the spectral responsivity (SR) and the current–voltage (I–V) curve have to be determined. The I–V curve then yields the characteristic parameters, including the power conversion efficiency, fill factor, short-circuit current and opencircuit voltage. The required measurement facilities and contacting stages are explained in detail; in addition, the measurement procedures are introduced. The precision and accuracy of the resulting characteristic parameters and curves are demonstrated by recent intercomparisons between different international calibration laboratories.
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J. Schmidt, K. Bothe, V. V. Voronkov, and R. Falster Fast and Slow Stages of Lifetime Degradation by Boron–Oxygen Centers in Crystalline Silicon Journal Article Forthcoming physica status solidi (b) 1900167, Forthcoming. Abstract | Links | BibTeX | Tags: defects, Lifetime, light-induced degradation (LID), recombination, silicon @article{Schmidt2019c,
title = {Fast and Slow Stages of Lifetime Degradation by Boron–Oxygen Centers in Crystalline Silicon}, author = {J Schmidt and K Bothe and V V Voronkov and R Falster}, doi = {10.1002/pssb.201900167}, year = {2019}, date = {2019-08-02}, journal = {physica status solidi (b)}, pages = {1900167}, abstract = {A conflict between previous and recently published data on the two-stage light-induced degradation (LID) of carrier lifetime in boron-doped oxygen-containing crystalline silicon is addressed. The previous experiments showed the activation of two boron–oxygen recombination centers with strongly differing recombination properties for the fast and slow stages of LID, whereas more recent studies found only a single center for both stages. To resolve this controversy, the historic silicon samples of these previous examinations are re-examined in this study after more than one decade. It is found that, in the historic samples, the fast stage can be either described by two different centers or a mixture of the two, depending on the duration of previous dark annealing. A possible solution is suggested based on the involvement of different activating impurities in the boron–oxygen defect. In dark-annealed samples, the defect consisting of boron, oxygen, and the activation impurity is present in two latent configurations, which reconfigure during LID at a fast and a slow stage. In the examined historic silicon samples, which did not undergo a gettering pretreatment, a significant concentration of an additional boron–oxygen defect with a different kind of activating impurity attached exists. The historic and modern results are thus reconciled.}, keywords = {defects, Lifetime, light-induced degradation (LID), recombination, silicon}, pubstate = {forthcoming}, tppubtype = {article} } A conflict between previous and recently published data on the two-stage light-induced degradation (LID) of carrier lifetime in boron-doped oxygen-containing crystalline silicon is addressed. The previous experiments showed the activation of two boron–oxygen recombination centers with strongly differing recombination properties for the fast and slow stages of LID, whereas more recent studies found only a single center for both stages. To resolve this controversy, the historic silicon samples of these previous examinations are re-examined in this study after more than one decade. It is found that, in the historic samples, the fast stage can be either described by two different centers or a mixture of the two, depending on the duration of previous dark annealing. A possible solution is suggested based on the involvement of different activating impurities in the boron–oxygen defect. In dark-annealed samples, the defect consisting of boron, oxygen, and the activation impurity is present in two latent configurations, which reconfigure during LID at a fast and a slow stage. In the examined historic silicon samples, which did not undergo a gettering pretreatment, a significant concentration of an additional boron–oxygen defect with a different kind of activating impurity attached exists. The historic and modern results are thus reconciled.
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D. Bredemeier, D. C. Walter, R. Heller, and J. Schmidt Impact of Hydrogen-Rich Silicon Nitride Material Properties on Light-Induced Lifetime Degradation in Multicrystalline Silicon Journal Article physica status solidi (RRL) – Rapid Research Letters 13 (8), 1900201, (2019). Abstract | Links | BibTeX | Tags: Carrier lifetime, Hydrogen, LeTID defects, light-induced lifetime degradation, silicon nitride, ulticrystalline silicon @article{Bredemeier2019b,
title = {Impact of Hydrogen-Rich Silicon Nitride Material Properties on Light-Induced Lifetime Degradation in Multicrystalline Silicon}, author = {D Bredemeier and D C Walter and R Heller and J Schmidt}, doi = {10.1002/pssr.201900201}, year = {2019}, date = {2019-08-01}, journal = {physica status solidi (RRL) – Rapid Research Letters}, volume = {13}, number = {8}, pages = {1900201}, abstract = {The root cause of “Light and Elevated Temperature Induced Degradation” (LeTID) of the carrier lifetime in multicrystalline silicon (mc-Si) wafers is investigated by depositing hydrogen-rich silicon nitride (SiNx:H) films of different compositions on boron-doped mc-Si wafers. The extent of LeTID observed in mc-Si after rapid thermal annealing (RTA) shows a positive correlation with the amount of hydrogen introduced from the SiNx:H layers into the bulk. The concentration of in-diffused hydrogen is quantified via measuring the resistivity change due to the formation of boron–hydrogen pairs in boron-doped float-zone silicon wafers processed in parallel to the mc-Si wafers. The measurements clearly show that the in-diffusion of hydrogen into the silicon bulk during RTA depends on both the atomic density of the SiNx:H film as well as the film thickness. Importantly, the impact of SiNx:H film properties on LeTID shows the same qualitative dependence as the hydrogen content in the silicon bulk, providing evidence that hydrogen is involved in the LeTID defect activation process.}, keywords = {Carrier lifetime, Hydrogen, LeTID defects, light-induced lifetime degradation, silicon nitride, ulticrystalline silicon}, pubstate = {published}, tppubtype = {article} } The root cause of “Light and Elevated Temperature Induced Degradation” (LeTID) of the carrier lifetime in multicrystalline silicon (mc-Si) wafers is investigated by depositing hydrogen-rich silicon nitride (SiNx:H) films of different compositions on boron-doped mc-Si wafers. The extent of LeTID observed in mc-Si after rapid thermal annealing (RTA) shows a positive correlation with the amount of hydrogen introduced from the SiNx:H layers into the bulk. The concentration of in-diffused hydrogen is quantified via measuring the resistivity change due to the formation of boron–hydrogen pairs in boron-doped float-zone silicon wafers processed in parallel to the mc-Si wafers. The measurements clearly show that the in-diffusion of hydrogen into the silicon bulk during RTA depends on both the atomic density of the SiNx:H film as well as the film thickness. Importantly, the impact of SiNx:H film properties on LeTID shows the same qualitative dependence as the hydrogen content in the silicon bulk, providing evidence that hydrogen is involved in the LeTID defect activation process.
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S. Müller, F. Giovannetti, R. Reineke-Koch, O. Kastner, and B. Hafner Simulation study on the efficiency of thermochromic absorber coatings for solar thermal flat-plate collectors Journal Article Solar Energy 188 , 865 - 874, (2019), ISSN: 0038-092X. Abstract | Links | BibTeX | Tags: Flat-plate collector, Selective absorber coating, stagnation, system simulation, thermochromic @article{Müller2019c,
title = {Simulation study on the efficiency of thermochromic absorber coatings for solar thermal flat-plate collectors}, author = {S Müller and F Giovannetti and R Reineke-Koch and O Kastner and B Hafner}, doi = {10.1016/j.solener.2019.06.064}, issn = {0038-092X}, year = {2019}, date = {2019-08-01}, journal = {Solar Energy}, volume = {188}, pages = {865 - 874}, abstract = {We present a comparative simulative study to evaluate the efficiency and stagnation behavior of commercially available absorber coatings for solar thermal flat-plate collectors. A market survey has revealed different absorber coatings, which exhibit solar absorptances of α > 90% and thermal emittances ε of 5–90%. All these coatings can be classified as wet-chemically electroplated coatings on the basis of black chrome, highly selective sputtered PVD coatings, solar paints and novel thermochromic coatings. We calculated the annual solar collector energy output by means of collector simulations with the tool ScenoCalc and compared the collector efficiency of several absorber coatings. We have carried out TRNSYS simulations both with systems for solar domestic hot water preparation and solar-assisted space heating. In a solar domestic hot water system with a daily tapping volume of 100 L we report an increase in the auxiliary energy demand of up to 6% with black chrome, 7% with thermochromic and 21% with solar paint coatings compared to sputtered PVD coatings. In a solar combisystem the increase in the auxiliary energy demand does not exceed 1.4% for thermochromic and black chrome coatings and 6.1% for solar paints. The stagnation period can be reduced from 178 h per year (PVD coatings) to 118 h, 62 h and 11 h for black chrome, thermochromic and solar paint coatings, respectively. The maximum absorber temperatures decrease from 175 °C (PVD coatings) to 165 °C for black chrome, 145 °C for thermochromic and 135 °C for solar paint coatings.}, keywords = {Flat-plate collector, Selective absorber coating, stagnation, system simulation, thermochromic}, pubstate = {published}, tppubtype = {article} } We present a comparative simulative study to evaluate the efficiency and stagnation behavior of commercially available absorber coatings for solar thermal flat-plate collectors. A market survey has revealed different absorber coatings, which exhibit solar absorptances of α > 90% and thermal emittances ε of 5–90%. All these coatings can be classified as wet-chemically electroplated coatings on the basis of black chrome, highly selective sputtered PVD coatings, solar paints and novel thermochromic coatings. We calculated the annual solar collector energy output by means of collector simulations with the tool ScenoCalc and compared the collector efficiency of several absorber coatings. We have carried out TRNSYS simulations both with systems for solar domestic hot water preparation and solar-assisted space heating. In a solar domestic hot water system with a daily tapping volume of 100 L we report an increase in the auxiliary energy demand of up to 6% with black chrome, 7% with thermochromic and 21% with solar paint coatings compared to sputtered PVD coatings. In a solar combisystem the increase in the auxiliary energy demand does not exceed 1.4% for thermochromic and black chrome coatings and 6.1% for solar paints. The stagnation period can be reduced from 178 h per year (PVD coatings) to 118 h, 62 h and 11 h for black chrome, thermochromic and solar paint coatings, respectively. The maximum absorber temperatures decrease from 175 °C (PVD coatings) to 165 °C for black chrome, 145 °C for thermochromic and 135 °C for solar paint coatings.
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M. R. Vogt, R. Witteck, T. Gewohn, H. Schulte-Huxel, C. Schinke, K. Bothe, and R. Brendel Ray Tracing of Complete Solar Cell Modules Inproceedings OSA Advanced Photonics Congress (AP) 2019 (IPR, Networks, NOMA, SPPCom, PVLED), PW2C.1, Optical Society of America, (2019). Abstract | Links | BibTeX | Tags: Antireflection coatings, Geometric optics, Material properties, ray tracing, Reflection, Solar Cells @inproceedings{Vogt2019,
title = {Ray Tracing of Complete Solar Cell Modules}, author = {M R Vogt and R Witteck and T Gewohn and H Schulte-Huxel and C Schinke and K Bothe and R Brendel}, url = {http://www.osapublishing.org/abstract.cfm?URI=PVLED-2019-PW2C.1}, year = {2019}, date = {2019-07-29}, booktitle = {OSA Advanced Photonics Congress (AP) 2019 (IPR, Networks, NOMA, SPPCom, PVLED)}, journal = {OSA Advanced Photonics Congress (AP) 2019 (IPR, Networks, NOMA, SPPCom, PVLED)}, pages = {PW2C.1}, publisher = {Optical Society of America}, abstract = {We use the Daidalos-Cloud module ray tracer to quantify optical losses in a PERC+ cell module in three different spectrally resolved irradiance conditions. In mean annual irradiation conditions 8.6 mA/cm^2 are lost, in contrast to 7.6 mA/cm^2 in STC.}, keywords = {Antireflection coatings, Geometric optics, Material properties, ray tracing, Reflection, Solar Cells}, pubstate = {published}, tppubtype = {inproceedings} } We use the Daidalos-Cloud module ray tracer to quantify optical losses in a PERC+ cell module in three different spectrally resolved irradiance conditions. In mean annual irradiation conditions 8.6 mA/cm^2 are lost, in contrast to 7.6 mA/cm^2 in STC.
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