We have fabricated P3HT and PCBM-based organic photovoltaic cells using DMDCNQI as a guest dopant material and an n-type buffer layer. We have investigated the physical effects of the DMD-CNQI molecule as a guest dopant and an n-type charge transfer buffer layer on the performance of the device by examining measurements of light current-voltage and photoluminescence characteristics. The device using DMDCNQI as a dopant and a buffer layer exhibited a remarkable increase in short-circuit current density (Jsc) due to the ability of an electron acceptor and to the formation of a highly conducting charge transfer complex. In particular, the device consisting of ITO/PEDOT:PSS/P3HT:PCBM:DMDCNQI(1 wt%)/DMDCNQ/Al showed a maximum power conversion efficiency of 3.50%.