Defect Engineering in Multinary Earth-Abundant Chalcogenide Photovoltaic Materials

Application of zinc-blende-related chalcogenide absorbers such as CdTe and Cu(In,Ga)Se-2 (CIGSe) has enabled remarkable advancement in laboratory-and commercial-scale thin-film photovoltaic performance; however concerns remain regarding the toxicity (CdTe) and scarcity (CIGSe/ CdTe) of the constituent elements. Recently, kesterite-based Cu2ZnSn(S,Se)(4) (CZTSSe) materials have emerged as attractive non-toxic and earth-abundant absorber candidates. Despite the similarities between CZTSSe and CIGSe/ CdTe, the record power conversion efficiency of CZTSSe solar cells (12.6%) remains significantly lower than that of CIGSe (22.6%) and CdTe (22.1%) devices, with the performance gap primarily being attributed to cationic disordering and associated band tailing. To capture the promise of kesterite-like materials as prospective drop-in earth-abundant replacements for closely-related CIGSe, current research has focused on several key directions to control disorder, including: (i) examination of the interaction between processing conditions and atomic site disorder, (ii) isoelectronic cation substitution to introduce ionic size mismatch, and (iii) structural diversification beyond the zinc-blende-type coordination environment. In this review, recent efforts targeting accurate identification and engineering of anti-site disorder in kesterite-based CZTSSe are considered. Lessons learned from CZTSSe are applied to other complex chalcogenide semiconductors, in an effort to develop promising pathways to avoid anti-site disordering and associated band tailing in future high-performance earth-abundant photovoltaic technologies.