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Rapid Recombination by Cadmium Vacancies in CdTe
Seán R Kavanagh1,2, Aron Walsh2,3, David O Scanlon1,4
1Thomas Young Centre and Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
ACS Energy Letters
|April 19, 2021
Summary
Cadmium vacancies (VCd) in cadmium telluride (CdTe) photovoltaics cause significant efficiency loss. Understanding their electronic behavior is key to improving solar energy conversion.
Area of Science:
- Materials Science
- Solid State Physics
- Renewable Energy Technologies
Background:
- Cadmium telluride (CdTe) is the leading thin-film photovoltaic technology.
- Non-radiative recombination limits CdTe solar conversion efficiency, with current records at 22% against a theoretical 32%.
- The role of cadmium vacancies (VCd) as acceptor species in p-type CdTe remains debated.
Purpose of the Study:
- To elucidate the structural and electronic behavior of cadmium vacancies (VCd) in CdTe.
- To reconcile theoretical predictions with experimental observations regarding VCd.
- To quantify the impact of VCd on charge-carrier recombination and solar cell efficiency.
Main Methods:
- Utilized *ab initio* defect calculations.
- Calculated the electronic structure and defect levels of VCd.
- Investigated the VCd 1- hole-polaron and associated structural phenomena.
Main Results:
- Calculated a negative-U double-acceptor level for VCd, consistent with experimental data.
- Observed VCd 1- hole-polaron formation, bridging theory and experiment.
- Identified tellurium dimerization, metastable structures, and anharmonic potentials as mechanisms for VCd-induced recombination.
Conclusions:
- Cadmium vacancies act as recombination centers in CdTe.
- These vacancies reduce maximum power conversion efficiency by over 5% in untreated CdTe.
- Understanding VCd behavior is crucial for advancing CdTe solar cell performance.
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