Organic-inorganic hybrid lead halide perovskites have recently been considered as competitive optical optoelectronic materials due to its advantages of solution processability, strong absorption, and high carrier mobility. In this work, we introduce a method for improving the morphology of perovskite films. Isopropanol (IPA) was introduced as additive to MAPbI3 precursor solution and one-step method was used to fabricate perovskite films with large grain size. Perovskite solar cells were prepared and the concentration of IPA was optimized. Power conversion efficiency of 14.6% was achieved by solar cells based on 6% v/v IPA solution, which enhance 40% compared with reference devices.