In this study, low-temperature sol-gel deposited ZnO thin films were employed as the electron-transport layer for planar type CH_3NH_3PbI_3 perovskite-based solar cells. The CH_3NH_3PbI_3 perovskite films were prepared under the atmosphere and their photovoltaic characteristics were discussed. Cells fabricated on the glass and flexible substrates exhibited good performance. The results show that record efficiencies of 12.8% (glass) and 9.7% (PET) were achieved under AM1.5G irradiation.