A large grain size perovskite thin film with a dense structure for planar heterojunction solar cells via spray deposition under ambient conditions

Organometal halide perovskites have emerged as promising light absorbers for third-generation photovoltaics. Herein we developed a facile spray deposition process to prepare high-quality perovskite films without any post-annealing under ambient conditions with a high humidity of up to 50%. The as-prepared perovskite films exhibit large grain sizes up to micrometers and full surface coverage. These desirable features significantly enhance the light harvesting efficiency and reduce charge recombination. Furthermore, the morphology and film thickness can be easily controlled by varying the precursor concentration or scanning times during spray deposition. The as-fabricated planar heterojunction solar cells with an optimized perovskite film thickness exhibited a power conversion efficiency of similar to 7.89%, which is expected to be further improved with the increase of substrate temperature, the utilization of more compatible substrates, and the optimization of the hole-transport layer and device structure. This simple low-temperature manufacturing process provides a novel strategy for the scalable and fast fabrication of high-quality absorber layers for efficient perovskite based solar cells. The film formation mechanism regarding the nucleation and growth of perovskite films with desirable morphology is also discussed.