Unraveling the colloidal composition of perovskite precursor solutions and its impact on film formation

Abstract

Colloids are a vital component of perovskite precursor solutions (PPSs), significantly influencing the quality of perovskite film formation. Despite their importance, a comprehensive understanding of these colloids remains elusive. In this work, we explored the colloidal compositions of two distinct PPS types: the monomer-mixing dissolution (MMD) and the pre-synthesized perovskite single crystal redissolution (SCR). We have uncovered a new dissolution chemical equilibrium mechanism where the transition from mixed monomers to the 3C cubic phase (α-phase) involves a reversible transformation. Our findings indicate that although colloidal size significantly affects the nucleation during perovskite crystallization, the composition of the colloids plays a more crucial role. The MMD method yields poly Pb-I·solvent clusters while the colloids derived from the SCR approach produce hexagonal lead-halide-based perovskite phase clusters. These divergent colloidal compositions lead to markedly different impacts on the perovskite film formation process. Notably, hexagonal-phase colloids act as favorable nucleation sites, promoting the generation of the α-phase perovskite films with larger grains, more homogeneous phases, and fewer defects. This work demonstrates the importance of tailoring colloidal compositions and provides theoretical insights into the beneficial effects of redissolving perovskite in forms such as powder, microcrystals, and single crystals.