We report on the fabrication and opto-electronic characterization of solution-processed planar heterojunction perovskite solar cells based on methylammonium (MA) lead halide derivatives, MAPbI3−xYx(Y = Cl, Br, I).

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We demonstrate a facile two-step low-pressure vapor deposition of methylammonium lead iodide (MAPbI 3 ) perovskite films in a single reactor. Continuous, polycrystalline lead iodide (PbI 2 ) films were deposited in the first step and successfully converted to high quality perovskite films in the second step during exposure of PbI 2 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 PbI 2 surface through the intercalation reaction of PbI 2 and MAI vapor molecules and progresses toward the PbI 2 /substrate interface. The coverage and quality of the perovskite thin film are controlled by that of the predeposited PbI 2 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%.