Monitoring the Phase Formation of Coevaporated Lead Halide Perovskite Thin Films by in Situ X‑ray Diffraction

Perovskite solar cells based on (CH3NH3)­Pb­(I,Cl)3 have recently demonstrated rapidly increasing cell efficiencies. Here, we show progress identifying phases present during the growth of (CH3NH3)­Pb­(I,Cl)3 perovskite thin films with the vacuum-based coevaporation approach using two sources under varying deposition conditions. With in situ X-ray diffraction, crystalline phases can be identified and monitored in real time. For different (CH3NH3)­I-to-PbCl2 flux ratios, two distinct (CH3NH3)­Pb­(I x Cl(1–x))3 phases with high (x > 0.95) and with lower (x < 0.5) iodine content as well as a broad miscibility gap in-between were found. During post deposition annealing we observe recrystallization and preferential orientation effects and finally the decomposition of the perovskite film to PbI2 at temperatures above 200 °C.