Solvent-Assisted Kinetic Trapping in Quaternary Perovskites

Engineering halide perovskites through alloying allows synthesis of materials having tuned electronic and optical properties; however, synthesizing many of these alloys is hindered by the formation of demixed phases arising due to thermodynamically unstable crystal structures. Methods have been developed to make such alloys, such as solid-phase reactions, chemical vapor deposition, and mechanical grinding; but these are incompatible with low-temperature solution-processing and monolithic integration, precluding a number of important applications of these materials. Here, solvent-phase kinetic trapping (SPKT), an approach that enables the synthesis of novel thermodynamically unfavored perovskite alloys, is developed. SPKT is used to synthesize Cs_{1- x} Rb_x PbCl₃ and report the first instance of ultraviolet emission in polycrystalline perovskite thin films. SPKT leads to materials exhibiting superior thermal and photostability compared to non-kinetically trapped materials of the same precursors. Transient absorption spectroscopy of the kinetically trapped material reveals improved optical properties: greater absorption, and longer ground-state bleach lifetimes. SPKT may be applied to other perovskites to realize improved material properties while benefiting from facile solution-processing.