Single crystal purification reduces trace impurities in halide perovskite precursors, alters perovskite thin film performance, and improves phase stability†

Impurities present in commercially available halide perovskite precursors are known to affect photovoltaic performance. Here, we employ bulk single crystal growth of FAPbI₃ using solvent orthogonality induced crystallization (SONIC) to remove a broad set of extrinsic impurities from commercially available halide perovskite precursors, as verified by detailed chemical analysis. Following SONIC purification, FAPbI₃ films made from PbI₂ of originally low purity (99%) and high purity (99.99%) show improved phase purity and stability under light and heat relative to films made from raw precursors or precursors purified via retrograde powder crystallization (RPC) in 2-methoxyethanol, a method commonly utilized in recent reports of the highest-efficiency perovskite solar cells. Single-crystal purification of precursors improves film stability under operational stressors, and the large enhancements in material purity provide a cleaner slate for improved isolation of compositional and additive effects on perovskite phase stability.