Minimizing voltage losses in Sn perovskite solar cells by Cs₂SnI₆ passivation

Abstract Stability and oxidation are major bottlenecks in improving the performance of Sn‐based perovskite solar cells. In this study, we present the formation of an n‐type Cs₂SnI₆ double‐perovskite (Sn‐DP) layer on a (PEAI)_0.15(FAI)_0.85SnI₂ perovskite (Sn‐P) layer using an orthogonal solution‐processable spray‐coating method. This novel approach achieves a minimized V_oc loss of 0.38 V and a PCE of 12.9% under 1 sun conditions. The n‐type DP layer effectively passivates tin vacancies, suppresses Sn²⁺ oxidation, reduces defects, and enhances electron extraction. Furthermore, the Sn‐DP/Sn‐P‐based solar cells exhibit excellent light‐soaking stability for 1000 h in the air under continuous one sun illumination, which is attributed to the stable Sn⁴⁺ state of the DP layer. Our experimental and theoretical investigations reveal that the type‐II band alignment between Sn‐DP and Sn‐P enhances the stability of the solar cells. The proposed Sn‐DP/Sn‐P architecture offers a promising pathway for developing Sn‐based solar cells. image