Homogenizing Nucleation and Growth of Tin Perovskite by Polarity-Free Trithiane Coordination Molecule for Efficient and Stable Photovoltaics

Tin (Sn)-based perovskite solar cells (TPSCs) have garnered significant attention recently, with power conversion efficiencies (PCEs) approaching 16%. Nevertheless, for Sn-based perovskites, their rapid crystallization and easy Sn²⁺ oxidation are always annoying for fabricating efficient and stable TPSCs. Coordination engineering has been developed for retarding the crystallization rate and Sn²⁺ passivation, but the homogeneous crystallization of Sn-based perovskites is still challenging due to the asymmetric and polar nature of currently used ligands. Here, a polarity-free S-containing symmetric molecule, 1,3,5-trithiane (TT), is developed to regulate the crystallization of FASnI₃. Nonpolar TT with three symmetric S atoms shows equally strong coordination with Sn²⁺, which enhances the environment stability of the precursor and promotes the homogeneous nucleation and retarded growth of FASnI₃ crystals. Consequently, TT-based TPSCs exhibit an improved PCE from 9.02% to 12.87% with robust stability. This study highlights the critical role of ligand polarity in controlling the crystallization behavior of efficient TPSCs.