Tin-Based Defects and Passivation Strategies in Tin-Related Perovskite Solar Cells

Tin (Sn)-based and mixed tin-lead (Sn-Pb) perovskites have attracted increased attention as promising candidates for new generation lead-free perovskite and all-perovskite tandem solar cells. However, as an inevitably critical issue, Sn(II) induced serious defects and oxidation and caused poor photovoltaic performance and unsatisfactory stability for Sn-based and mixed Sn-Pb perovskites. Herein, a comprehensive understanding on defect classification, defect formation, defect effect on performance, and defect passivation strategies is reviewed on the Sn(II) induced defects. The Sn(II)-based defects can be classified from the aspects of defect dimensions and shallow/deep levels in energy structure according to three main origins, i.e. low defect tolerance, oxidation, and fast crystallization. Then, the state-of-the-art defect passivation strategies including surface Lewis acid/base coordination, low/mixed dimensional perovskite design, composition regulation and crystal orientation modulation, and reducing agent assistance are summarized systematically. Lastly, several key scientific issues and future research prospectives are proposed for achieving stable and high-performance Sn-related perovskite photovoltaics.