| Summary: | Solution-processed organometal halide perovskites (OMHPs) have been widely used in optoelectronic devices, and have exhibited brilliant performance. One of their generally recognized advantages is their easy fabrication procedure. However, such a procedure also brings uncertainty about the opto-electric properties of the final samples and devices, including morphology, stability, coverage ratio, and defect concentration. Normally, one needs to find a balanced condition, because there is a competitive relation between these parameters. In this work, we fabricated CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films by carefully changing the ratio of the PbI<sub>2</sub> to CH<sub>3</sub>NH<sub>3</sub>I, and found that the stoichiometric and solvent engineering not only determined the photoluminescence efficiency and defects in the materials, but also affected the photostability, morphology, and coverage ratio. Combining solvent engineering and the substitution of PbI<sub>2</sub> by Pb(Ac)<sub>2</sub>, we obtained an optimized fabrication condition, providing uniform CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films with both high photoluminescence efficiency and high photostability under either I-rich or Pb-rich conditions. These results provide an optimized fabrication procedure for CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> and other OMHP films, which is crucial for the performance of perovskite-based solar cells and light emitting devices.
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