Influence of Solvent Coordination on Hybrid Organic-Inorganic Perovskite Formation

Solution-processed hybrid organic-inorganic perovskites (HOIPs) from organoammonium halide and lead halide precursors form efficacious active layers for photovoltaics, light-emitting diodes, and flexible electronics. Though solvent-solute coordination plays a critical role in HOIP crystallization, the influence of solvent choice on such interactions is poorly understood. We demonstrate Gutmann's donor number, D_N, as a parameter that indicates the coordinating ability of the processing solvent with the Pb²⁺ center of the lead halide precursor. Low D_N solvents interact weakly with the Pb²⁺ center, favoring instead complexation between Pb²⁺ and iodide and subsequent crystallization of perovskite. High D_N solvents coordinate more strongly with the Pb²⁺ center, which in turn inhibits iodide coordination and stalls perovskite crystallization. Varying the concentration of high-D_N additives in precursor solutions tunes the strength of lead-solvent interactions, allowing finer control over the crystallization and the resulting morphology of HOIP active layers.