The synergistic effect of H2O and DMF towards stable and 20% efficiency inverted perovskite solar cells

Abstract

A high quality thick (500 nm) CH₃NH₃PbI₃ perovskite absorber with a horizontal grain size up to 3 μm and a lateral size equal to the film thickness was prepared by the synergistic effect of a H₂O additive and DMF vapor treatment via a two-step spin coating method. The inverted (p–i–n) cell based on this high-quality thick perovskite film achieves a high power conversion efficiency of 20.1%. The cell shows no current hysteresis and is stable in inert and ambient atmospheres with appropriate encapsulation. H₂O helps MAI to penetrate into the thick PbI₂ to form a thick film with a pure MAPbI₃ phase and produces bigger gains by slowing down the perovskite crystallization rate. It can also cooperate with DMF to control the dissolution of perovskite grains during DMF vapor post treatment. As a result, large multi-crystalline perovskite grains without observable holes and creases are formed when DMF and H₂O were removed during the following heating process. The synergistic effect of H₂O and DMF was evidenced by SEM images and GIWXRD patterns taken simultaneously. This synergistic strategy for preparing a high-quality, thick perovskite film was extended to fabricate a large-area MAPbI₃ film (1.3 cm² and 11.25 cm² for the cell and mini-module, respectively) to realize an efficiency of 16.7 and 15.4%.