1.
V Steckenreiter; D C Walter; J Schmidt
In: Energy Procedia, Bd. 124, Nr. Supplement C, S. 799-805, 2017, ISSN: 1876-6102, (7th International Conference on Silicon Photovoltaics, SiliconPV 2017, 3-5 April 2017, Freiburg, Germany).
@article{Steckenreiter2017c,
title = {Two-stage permanent deactivation of the boron-oxygen-related recombination center in crystalline silicon},
author = {V Steckenreiter and D C Walter and J Schmidt},
doi = {10.1016/j.egypro.2017.09.350},
issn = {1876-6102},
year = {2017},
date = {2017-09-21},
journal = {Energy Procedia},
volume = {124},
number = {Supplement C},
pages = {799-805},
abstract = {We analyze the lifetime evolution during permanent deactivation of the boron-oxygen-related defect center (BO defect) in boron-doped, oxygen-rich Czochralski-grown silicon (Cz-Si). In particular, we examine the impact of the samples’ states prior to the permanent deactivation process. Samples that were initially fully degraded show a two-stage deactivation process consisting of a fast and a slow deactivation component, which can be fitted by two exponential functions with their respective rate constants. For both components, we find a pronounced increase of the rate constants with illumination intensity. In addition, we observe that the rate constant describing the slow deactivation component of samples deactivated after complete degradation is identical to the rate constant determined on samples, which were deactivated immediately after annealing in darkness. In the latter case, a purely mono-exponential deactivation behavior was observed. Our study clearly demonstrates that the asymptotic deactivation behavior does not depend on the initial state of the lifetime sample. We prove that the same is valid for initially degraded and dark-annealed PERC solar cells. Hence, it is not necessary to first degrade the sample to realize a fast BO deactivation.},
note = {7th International Conference on Silicon Photovoltaics, SiliconPV 2017, 3-5 April 2017, Freiburg, Germany},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We analyze the lifetime evolution during permanent deactivation of the boron-oxygen-related defect center (BO defect) in boron-doped, oxygen-rich Czochralski-grown silicon (Cz-Si). In particular, we examine the impact of the samples’ states prior to the permanent deactivation process. Samples that were initially fully degraded show a two-stage deactivation process consisting of a fast and a slow deactivation component, which can be fitted by two exponential functions with their respective rate constants. For both components, we find a pronounced increase of the rate constants with illumination intensity. In addition, we observe that the rate constant describing the slow deactivation component of samples deactivated after complete degradation is identical to the rate constant determined on samples, which were deactivated immediately after annealing in darkness. In the latter case, a purely mono-exponential deactivation behavior was observed. Our study clearly demonstrates that the asymptotic deactivation behavior does not depend on the initial state of the lifetime sample. We prove that the same is valid for initially degraded and dark-annealed PERC solar cells. Hence, it is not necessary to first degrade the sample to realize a fast BO deactivation.
2.
D C Walter; J Schmidt
In: Solar Energy Materials and Solar Cells, Bd. 158, S. 91-97, 2016, (Proceedings of the 6th International Conference on Silicon Photovoltaics (SiliconPV)).
@article{Walter2016c,
title = {Impact of hydrogen on the permanent deactivation of the boron-oxygen-related recombination center in crystalline silicon},
author = {D C Walter and J Schmidt},
doi = {10.1016/j.solmat.2016.05.025},
year = {2016},
date = {2016-12-01},
journal = {Solar Energy Materials and Solar Cells},
volume = {158},
pages = {91-97},
abstract = {In a series of lifetime experiments, we examine the impact of hydrogen on the permanent deactivation of the boron-oxygen (BO)-related defect center in Czochralski-grown boron-doped silicon. In the first experiment, the hydrogen concentration in the external source is varied by the deposition of dielectric layers containing various hydrogen concentrations (aluminum oxide and silicon nitride layers) before applying a fast-firing step at high temperature (>800 °C). In the second experiment, the sample cooling rate after high-temperature treatment is varied without hydrogen-rich dielectric layer being present and the surface passivation based on aluminum oxide is applied at low temperature afterwards. In both experiments, it is observed that the sample cooling after the high-temperature treatment has the major impact on the dynamics of BO deactivation process and fast cooling rates enable a fast deactivation. No direct impact of the hydrogen content in the dielectric layers being present during the fast-firing step on the dynamics of the BO deactivation is observed. However, the highest lifetimes in excess of 1 ms are only achievable when a hydrogenation step is performed, which we interpret in terms of a hydrogen passivation of background defects of hitherto unknown nature. In a third experiment, we apply an organic passivation layer by spin-coating, which is dried at low temperature (130 °C). We find in this experiment that even without any hydrogen intentionally introduced into the silicon bulk, an effective deactivation of the BO center can be observed, clearly supporting that no hydrogen is required to enable the BO deactivation.},
note = {Proceedings of the 6th International Conference on Silicon Photovoltaics (SiliconPV)},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In a series of lifetime experiments, we examine the impact of hydrogen on the permanent deactivation of the boron-oxygen (BO)-related defect center in Czochralski-grown boron-doped silicon. In the first experiment, the hydrogen concentration in the external source is varied by the deposition of dielectric layers containing various hydrogen concentrations (aluminum oxide and silicon nitride layers) before applying a fast-firing step at high temperature (>800 °C). In the second experiment, the sample cooling rate after high-temperature treatment is varied without hydrogen-rich dielectric layer being present and the surface passivation based on aluminum oxide is applied at low temperature afterwards. In both experiments, it is observed that the sample cooling after the high-temperature treatment has the major impact on the dynamics of BO deactivation process and fast cooling rates enable a fast deactivation. No direct impact of the hydrogen content in the dielectric layers being present during the fast-firing step on the dynamics of the BO deactivation is observed. However, the highest lifetimes in excess of 1 ms are only achievable when a hydrogenation step is performed, which we interpret in terms of a hydrogen passivation of background defects of hitherto unknown nature. In a third experiment, we apply an organic passivation layer by spin-coating, which is dried at low temperature (130 °C). We find in this experiment that even without any hydrogen intentionally introduced into the silicon bulk, an effective deactivation of the BO center can be observed, clearly supporting that no hydrogen is required to enable the BO deactivation.
3.
D Walter; T Pernau; J Schmidt
Ultrafast lifetime regeneration in an industrial belt-line furnace applying intense illumination at elevated temperature Proceedings Article
In: WIP, (Hrsg.): Proceedings of the 32nd European Photovoltaic Solar Energy Conference, S. 469-473, Munich, Germany, 2016, ISBN: 3-936338-41-8.
@inproceedings{Walter2016,
title = {Ultrafast lifetime regeneration in an industrial belt-line furnace applying intense illumination at elevated temperature},
author = {D Walter and T Pernau and J Schmidt},
editor = {WIP},
doi = {10.4229/EUPVSEC20162016-2DO.1.1},
isbn = {3-936338-41-8},
year = {2016},
date = {2016-09-01},
booktitle = {Proceedings of the 32nd European Photovoltaic Solar Energy Conference},
journal = {Proceedings of the 32nd European Photovoltaic Solar Energy Conference},
pages = {469-473},
address = {Munich, Germany},
abstract = {Solar cells made of boron-doped, oxygen-rich Czochralski-grown silicon (Cz-Si) wafers suffer from a degradation in conversion efficiency upon illumination. This effect, sometimes labeled “light-induced degradation” (LID), is caused by a defect center within the silicon bulk, often referred to as BO defect, which activates its recombination properties under illumination leading to a degradation of the carrier lifetime. However, the BO defect center can be permanently deactivated, i.e. the lifetime can be permanently recovered, under illumination at elevated temperature. Within this contribution, we focus on transferring our lab-type BO deactivation process, using a hotplate and a halogen lamp, into an ultrafast high-throughput process, applying an industrial-type belt-furnace especially designed for this very purpose by centrotherm photovoltaics AG. Using this industrial furnace, inline processing in a solar cell production line is feasible. Our investigation clearly shows that a permanent recovery of the lifetime with an industrial belt-furnace can be achieved. In addition, we prove this result also for a shorter lab-type version of the longer industrial belt-furnace. The lifetimes reached after processing can be comparable to the lifetimes obtained on the same Cz-Si materials after applying our lab-type approach. Excellent stability of the lifetime is verified for up to 1000 hours of illumination at room temperature.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Solar cells made of boron-doped, oxygen-rich Czochralski-grown silicon (Cz-Si) wafers suffer from a degradation in conversion efficiency upon illumination. This effect, sometimes labeled “light-induced degradation” (LID), is caused by a defect center within the silicon bulk, often referred to as BO defect, which activates its recombination properties under illumination leading to a degradation of the carrier lifetime. However, the BO defect center can be permanently deactivated, i.e. the lifetime can be permanently recovered, under illumination at elevated temperature. Within this contribution, we focus on transferring our lab-type BO deactivation process, using a hotplate and a halogen lamp, into an ultrafast high-throughput process, applying an industrial-type belt-furnace especially designed for this very purpose by centrotherm photovoltaics AG. Using this industrial furnace, inline processing in a solar cell production line is feasible. Our investigation clearly shows that a permanent recovery of the lifetime with an industrial belt-furnace can be achieved. In addition, we prove this result also for a shorter lab-type version of the longer industrial belt-furnace. The lifetimes reached after processing can be comparable to the lifetimes obtained on the same Cz-Si materials after applying our lab-type approach. Excellent stability of the lifetime is verified for up to 1000 hours of illumination at room temperature.