We prepared the porous and single crystal ZnO nanoflowers with differe nt hydrothermal reaction time (6h,9h and 12h).The morphology and photoelectrical properties of the porous ZnO nanoflowers are investigated.The results reveal that the porous ZnO nanoflowe rs with reaction time of 9h are ideal electron-selective layers,since they hav e some excellent characteristics,such as superior light transmittance,low defect density,and high carrier mobility.Finall y,ZnO nanoflowers are employed in the organic solar cells as electron-selective layer.Compared with the control device without ZnO interlayer,the optimized device with ZnO interlayer grown for 9h show s a higher short circuit current density and photoelectric conversion efficiency,which are 5.68mA/cm^2and 1.24%,respectively.