Low‐Temperature Preparation of High‐Quality Perovskite Polycrystalline Films via Crystallization Kinetics Engineering

Preparation of lead halide perovskite polycrystalline films at a low annealing temperature is highly restricted by their intrinsically large crystallization activation energy, which hinders the conversion of the precursors/intermediates to perovskites and yields as‐prepared polycrystals with tiny grain sizes and terrible crystal quality. Herein, we demonstrate through in‐situ, real‐time spectroscopic studies that both the nucleation and crystal growth kinetics can be improved without the need for a high annealing temperature by treating the film with thiourea, as accounted for by the reduced activation energy. As a consequence, the thiourea‐treated perovskite polycrystalline film exhibits larger grain sizes and greater crystallinity than the untreated one. More importantly, owing to the synergistic effect of the promoted crystallization kinetics and the passivation of surface defects, the low‐temperature prepared films treated with thiourea even present more prominent photophysical properties than those fabricated by using the conventional high‐temperature method. The strategy of crystallization kinetics engineering proposed in this work paves the way for fabricating high‐quality perovskite polycrystalline films in a low‐temperature manner. Engineering the crystallization kinetics of perovskite polycrystals via a feasible thiourea treatment method enables the fabrication of high‐quality perovskite polycrystalline films at low temperature.