Solvent vapor annealing of oriented PbI₂ films for improved crystallization of perovskite films in the air

The photovoltaic performance of perovskite solar cells is extremely dependent on the crystallization and morphology of the perovskite film, which are affected by the deposition method. Here, we demonstrate a simple approach to form a microporous PbI₂ film, with subsequent conversion to a compact, highly crystalline perovskite film. The PbI₂ and corresponding perovskite films were further probed by two-dimensional X-ray diffraction. The resultant perovskite exhibited improved photovoltaic performance under ambient conditions with about 50% humidity. The PbI₂ microporous structure was formed by exchanging residual DMSO with DMF vapor in the PbI₂ film, which facilitated contact with the methylammonium iodide (MAI) solution. The process resulted in the formation of compact, smooth, pinhole-free perovskite films having no residual PbI₂. Solar cells fabricated using this methodology exhibited power conversion efficiencies over 16% with negligible photocurrent hysteresis.