Abstract
Monocrystalline Si solar cells are fabricated from Czochralski (Cz) Si, which contains 1017-1018 cm-3 oxygen atoms. Cz Si undergoes degradation during high-temperature thermal processing steps, such as dopant diffusion to form the p-n junction. This degradation in the bulk minority carrier lifetime can be related to the formation of oxygen precipitates. We found that a high-temperature annealing process known as tabula rasa (TR) not only mitigates process-induced degradation via oxygen precipitate nuclei dissolution, but also modifies subsequent light-induced degradation. We report on the bulk carrier lifetime of n- and p-type Cz Si after TR, which homogenizes the interstitial oxygen in the bulk Si to its monoatomic form in either an N2 or O2 environment. A control sample, which was not subjected to a TR processing step, experienced severe process-induced degradation during a boron emitter thermal budget as oxygen precipitates were formed in the Si bulk. These precipitates could be imaged using photoluminescence. Additionally, samples that underwent a TR processing step prior to the boron emitter thermal budget show efficient gettering of metallic impurities compared to the control sample, which showed a decline in the implied open-circuit voltage after the gettering step. Furthermore, modification of the interstitial oxygen bonding by TR had a strong effect on the light-induced degradation kinetics. Instead of a typically observed monotonic decrease, minority carrier lifetime increases first, followed by a nonmonotonic decrease over a ∼20 h period. We conclude that by modifying the interstitial oxygen bonding via TR pretreatment, p-type Cz Si wafers become substantially resistant to harsh solar cell processes and strongly modified light-induced degradation, which would open alternative ways to mitigate this degradation mechanism.
Original language | American English |
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Article number | 9195837 |
Pages (from-to) | 1557-1565 |
Number of pages | 9 |
Journal | IEEE Journal of Photovoltaics |
Volume | 10 |
Issue number | 6 |
DOIs | |
State | Published - Nov 2020 |
Bibliographical note
Publisher Copyright:© 2011-2012 IEEE.
NREL Publication Number
- NREL/JA-5900-77729
Keywords
- Degradation
- oxygen precipitation
- silicon solar cell
- tabula rasa