Thiazole-Induced Surface Passivation and Recrystallization of CH₃NH₃PbI₃ Films for Perovskite Solar Cells with Ultrahigh Fill Factors

The quality of perovskite films is a crucial factor governing the photovoltaic performance of perovskite solar cells. However, perovskite films fabricated by the conventional one-step spin-coating procedure are far from ideal due to uncontrollable crystal growth. Herein, we report a facile recrystallization procedure using a thiazole additive coupled with vapor annealing to simultaneously modulate the perovskite crystal growth and suppress the surface defects. High quality perovskite films with no pin holes, high crystallinity, large grain size, and low roughness were obtained. Moreover, using the space charge limited current method, we observe that the defect density of the as-prepared perovskite films with the thiazole additive was decreased by 40% when compared with the film without thiazole. The lower defect density of these perovskite films enables the achievement of a final power conversion efficiency of 18% and an exceptionally high fill factor of 0.82, which correspond to a 25% enhancement compared with the control device. Our results reveal a novel and facile path to modulate the perovskite crystal growth and simultaneously suppress the film defect density and increasing efficiency in perovskite photovoltaics and related optoelectronic applications.