Air-Stable Hybrid Perovskite Solar Cell by Sequential Vapor Deposition in a Single Reactor

We demonstrate a facile two-step low-pressure vapor deposition of methyl­ammonium lead iodide (MAPbI₃) perovskite films in a single reactor. Continuous, polycrystalline lead iodide (PbI₂) films were deposited in the first step and successfully converted to high quality perovskite films in the second step during exposure of PbI₂ films to methyl­ammonium iodide (MAI) vapor. A complete conversion was realized after 90 min of exposure with an average grain size of 3.70 ± 1.80 μm. The perovskite conversion starts at the PbI₂ surface through the intercalation reaction of PbI₂ and MAI vapor molecules and progresses toward the PbI₂/substrate interface. The coverage and quality of the perovskite thin film are controlled by that of the predeposited PbI₂ film. The absorbance measurements confirmed air stability of the fully converted perovskite for 21 days, ascribed to its superior morphology and grain size. Finally, a planar single-junction perovskite solar cell with no additives or additional interfacial engineering was fabricated and tested under open-air conditions, yielding a best power conversion efficiency of 11.7%. The solar cell maintains 85% of its performance up to 13 days in the open air with a relative humidity up to 80%.