Defect suppression in multinary chalcogenide photovoltaic materials derived from kesterite: progress and outlook

The performance of many emerging multinary chalcogenides for photovoltaic application is considerably inferior than the Shockley–Queisser limit, and one of the main reasons for this is the existence of various detrimental deep-level defects and defect clusters. Among them, the development of kesterite-based Cu2ZnSn(Sx,Se1–x)4 (CZTCh) solar cells is currently hindered by a large open-circuit voltage deficit (Voc,def). Much of this Voc,def has been ascribed to abundant cation disorder and defect clusters in CZTSSe absorber layer, which is the origin of band-tail states caused by the electrostatic potential fluctuations. To deal with the above intractable trouble encountered in kesterite-like materials, a partial or complete cations substitution offers a viable pathway to alter the characteristics of those deleterious defects and defects clusters, including (i) the partial cation substitution can introduce ionic size mismatch for alleviating antisite disorder and/or detrimental defect clusters to mitigate large Voc,def; (ii) the complete cation substitution can be expected to eliminate notorious band-tail states, and develop/explore many emerging multinary chalcogenides beyond the kesterite CZTSSe for photovoltaic application. In this review, we summarized the above recent efforts and attempts both in state-of-the-art experimental studies and also in gaining new theoretical insights to treat the problem of CZTSSe, and learn its lesson for applying to the other promising chalcogenide photovoltaics. In addition, the record efficiencies for cation-substituted kesterite and related MI2-MII- MIV-Ch4 chalcogenides PV devices reported up to date were summarized in this review. Finally, a summary and outlook are provided on research trends regarding the improvement of kesterite-based devices, as well as the exploration of related chalcogenides photovoltaic (PV) materials.