ZnO thin films prepared by spin-coating of nanoparticles at low temperature were utilized as the electron collection layer in CH3NH3PbI3-based perovskite solar cells having a planar heterojunction structure. The thickness of ZnO layer as a key parameter to determine the photovoltaic performance was optimized. The highest power conversion efficiency of up to 13.9% with small hysteretic behavior of current voltage curves was achieved under AM 1.5 illumination (100 mW cm(-2)). The ZnO-based devices exhibited significantly improved durability as compared to the control device with exposure to the ambient air environment.