Solvent-Mediated Crystallization of CH₃NH₃SnI₃Films for Heterojunction Depleted Perovskite Solar Cells

TLDR

Lead‑based perovskite solar cells reach ~20 % efficiency, yet lead toxicity raises environmental concerns. The study investigates how solvent choice influences the crystallization of lead‑free methylammonium tin triiodide (CH₃NH₃SnI₃) films during solution growth. Using a DMSO solution, a transitional SnI₂·3DMSO intermediate phase is formed, producing highly uniform, pinhole‑free CH₃NH₃SnI₃ films. These films enable heterojunction depleted solar cells without a hole‑transport material, achieving photocurrents up to 21 mA cm⁻², high carrier densities, and comparable recombination lifetimes to Pb analogues, though lower efficiency is attributed to a higher background dark carrier density, demonstrating progress toward efficient lead‑free perovskite solar cells.

Abstract

Organo-lead halide perovskite solar cells have gained enormous significance and have now achieved power conversion efficiencies of ∼20%. However, the potential toxicity of lead in these systems raises environmental concerns for widespread deployment. Here we investigate solvent effects on the crystallization of the lead-free methylammonium tin triiodide (CH3NH3SnI3) perovskite films in a solution growth process. Highly uniform, pinhole-free perovskite films are obtained from a dimethyl sulfoxide (DMSO) solution via a transitional SnI2·3DMSO intermediate phase. This high-quality perovskite film enables the realization of heterojunction depleted solar cells based on mesoporous TiO2 layer but in the absence of any hole-transporting material with an unprecedented photocurrent up to 21 mA cm(-2). Charge extraction and transient photovoltage decay measurements reveal high carrier densities in the CH3NH3SnI3 perovskite device which are one order of magnitude larger than CH3NH3PbI3-based devices but with comparable recombination lifetimes in both devices. The relatively high background dark carrier density of the Sn-based perovskite is responsible for the lower photovoltaic efficiency in comparison to the Pb-based analogues. These results provide important progress toward achieving improved perovskite morphology control in realizing solution-processed highly efficient lead-free perovskite solar cells.