Rapid Recombination by Cadmium Vacancies in CdTe

Seán R Kavanagh; Aron Walsh; David O Scanlon

doi:10.1021/acsenergylett.1c00380

Rapid Recombination by Cadmium Vacancies in CdTe

ACS Energy Lett. 2021 Apr 9;6(4):1392-1398. doi: 10.1021/acsenergylett.1c00380. Epub 2021 Mar 19.

Authors

Seán R Kavanagh^{1

2}, Aron Walsh^{2

3}, David O Scanlon^{1

4}

Affiliations

¹ Thomas Young Centre and Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
² Thomas Young Centre and Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.
³ Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.
⁴ Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, U.K.

Abstract

CdTe is currently the largest thin-film photovoltaic technology. Non-radiative electron-hole recombination reduces the solar conversion efficiency from an ideal value of 32% to a current champion performance of 22%. The cadmium vacancy (V_Cd) is a prominent acceptor species in p-type CdTe; however, debate continues regarding its structural and electronic behavior. Using ab initio defect techniques, we calculate a negative-U double-acceptor level for V_Cd, while reproducing the V_Cd ^1- hole-polaron, reconciling theoretical predictions with experimental observations. We find the cadmium vacancy facilitates rapid charge-carrier recombination, reducing maximum power-conversion efficiency by over 5% for untreated CdTe-a consequence of tellurium dimerization, metastable structural arrangements, and anharmonic potential energy surfaces for carrier capture.