The synergistic effect of cooperating solvent vapor annealing for high-efficiency planar inverted perovskite solar cells

Solvent vapor annealing (SVA) is an effective post-treatment process to improve the quality of crystals and grains in metal halide perovskite films. Whereas SVA has been successfully adopted for the fabrication of perovskite films via the conventional two-step method, its adaptation to the simple single-step perovskite film deposition method has been limited because of the rapid transition of the precursor to the perovskite structure. In the present study, we demonstrate highly efficient and stable single-stepbased inverted perovskite solar cells fabricated with perovskite films prepared using dimethyl sulfoxide (DMSO) and water as a combined solvent in SVA treatment. The treatment with DMSO alone resulted in the growth of large grains (similar to 900 nm) in the lateral direction at the surface region; however, voids and defects were observed in the vertical direction at the bottom interfacial region of the CH3NH3PbI3 layer, which resulted in poor device properties. Interestingly, the combined DMSO-water induced vertical growth of almost single grains and the healing effect of water improved the grain quality. As a result, we fabricated co-SVA CH3NH3PbI3 devices with a power conversion efficiency (PCE) of 19.52%. This PCE, which is much higher than that of pristine devices, was attributed to reduced nonradiative recombination. In addition, co-SVA solar cells displayed remarkable stability and their universality in various types of perovskite materials was demonstrated. We anticipate that our proposed process and mechanism will be widely used in the future development of perovskite-based devices.