Microstructure modulation of the CH3NH3PbI3 layer in perovskite solar cells by 2-propanol pre-wetting and annealing in a spray-assisted solution process

Abstract

As the light absorption layer, a CH₃NH₃PbI₃ perovskite film with a fully and homogeneously covered flat surface is crucially important for perovskite photovoltaic devices. Herein, the sequential method is improved by introducing a spray-assisted solution process (SSP) instead of the commonly used dipping process in CH₃NH₃PbI₃ perovskite film deposition. The morphology analysis for PbI₂ films found that the airflow of the spray pre-wetting process provides a driving force for accelerating the dissolution and deep infiltration, which is helpful to form a mesoporous PbI₂ scaffold. So the 2-propanol (IPA) pre-wetting has advantages to complete the reaction of PbI₂ and CH₃NH₃I through the diffusion channel in the grain boundary and on the surface of the PbI₂ film. Furthermore, the grain size and surface coverage of the film can be controlled effectively by a facile IPA pre-wetting process in the SSP. Meanwhile, the influence of the annealing process on the crystallization, chemical composition, microstructures and carrier transport properties of the perovskite films were investigated. Our results showed that an optimum annealing temperature and time can reduce crystal defects in the film and weaken the hysteresis phenomenon of the perovskite solar cell. Efficient mesoporous structured perovskite solar cells were fabricated with an optimal PCE of 14.2%, because of the improved perovskite film preparation method.