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 (VCd) 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 VCd, while reproducing the VCd 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.
Bibliographical noteFunding Information:
We thank Dr. Anna Lindström for valuable discussions regarding polaronic structures for cadmium vacancies, and Dr. Sungyhun Kim for assistance with CarrierCapture.jl calculations. S.R.K. acknowledges the EPSRC Centre for Doctoral Training in the Advanced Characterisation of Materials (CDT-ACM)(EP/S023259/1) for funding a Ph.D. studentship. We acknowledge the use of the UCL Grace High Performance Computing Facility (Grace@UCL), the Imperial College Research Computing Service, and associated support services, in the completion of this work. Via membership of the UK’s HEC Materials Chemistry Consortium, which is funded by the EPSRC (EP/L000202, EP/R029431, EP/T022213), this work used the ARCHER UK National Supercomputing Service ( www.archer.ac.uk and the UK Materials and Molecular Modelling (MMM) Hub (Thomas EP/P020194 and Young EP/T022213).
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