Abstract: This study focuses on the PTB7:PCBM material system,applying Photo-CELIV technique to analyze the effect of the donor/acceptor ratio. In this study,is discovered that charge mobility and recombination rate change with the contents ratio inside the material system. The highest power conversion efficiency of 7.1% is achiened at the donor/acceptor ratio of 1∶1.5 in the PTB7∶PCBM system. The blends with this optimal ratio also exhibited highest charge mobility and lowest recombination rate. The AFM images confirm that in the semiconductor film with optimized contents ratio,the uniform phase separation is beneficial to the increase of the fill factor,thereby improving the efficiency. The present study provides quantitative analysis basis for improving the power conversion efficiency of organic photovoltaic devices.