Organometallic halide perovskite-based solar cells have exhibited rapidly increasing efficiencies through the use of mesoporous composites. The addition of materials used in organic solar cells to perovskite-based solar cells (PSCs) enables the fabrication of low-cost, flexible, low-temperature, solution-processed PSCs. However, obtaining sufficient coverage of the organic layer, usually poly­(3,4-ethylenedioxythiophene)–poly­(styrenesulfonate) (PEDOT:PSS), with CH3NH3PbI3–x Cl x films remains difficult in spite of the advances. In this study, we investigated the influence of controlling the solvent evaporation rate on the degree of PEDOT:PSS surface coverage by CH3NH3PbI3–x Cl x . We determined that an adequately fast spinning speed, drying at room temperature, and stepwise ramp annealing are critical for obtaining optimized planar hybrid perovskite solar cells with an ITO/PEDOT:PSS/CH3NH3PbI3–x Cl x /PCBM/Al structure and efficiencies of up to 11.8%.