Efficient Tin (II) Fluoride‐Free Formamidinium Tin Triiodide Perovskite Solar Cells via Composition and Additive Engineering.

Tin halide perovskite solar cells (TPSCs) have attracted extensive attention because of their low toxicity and high theoretical efficiency. However, rapid crystallization, rich defects, and easy oxidation of tin‐based perovskite films seriously restrict solar cell performance. Herein, a composition and additive engineering solution by removing commonly used tin fluoride additive from formamidinium tin triiodide perovskite precursors and replacing it with excess tin (II) iodide and ethylenediamine dihydroiodide (EDAI2) is adopted. The presence of EDAI2 and excess SnI2 and the absence of SnF2 enable tin‐based perovskite films with greatly improved morphology, enhanced crystalline quality, boosted optical properties, and prolonged carrier lifetime. Therefore, the SnF2‐free non‐stoichiometric TPSCs employing the EDAI2 additive and excess SnI2 have increased built‐in potential, lowered dark currents, and reduced carrier recombination. The resulting SnF2‐free and SnI2‐rich TPSCs with EDAI2 addition realize a steady‐state efficiency of 10.0%, which is one of the highest power conversion efficiencies among the SnF2‐free TPSCs, along with considerably improved light stability. This work highlights the crucial roles of additives in TPSCs and provides an effective strategy to fabricate efficient and stable low‐toxic lead‐free perovskite solar cells. [ABSTRACT FROM AUTHOR]