The effect of a new interfacial buffer layer material,rhenium oxide(ReO3),on the performance of polymer solar cells based on regioregular poly(3-hexylthiophene)(P3HT) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester(PCBM) blend is investigated.The effect of the thickness of the oxide layer on electrical characteristics of the device is also studied.Compared with traditional devices,by inserting a 10 nm-thick ReO3 as the anode buffer layer,a power conversion efficiency(PCE) of 2.8 %(a 37% improvement compared with the control devices) can be obtained with Jsc of 13.6 mA/cm2,Voc of 0.45 V,and a fill factor(FF) of 53.6% under the simulated AM1.5 G 100 mW/cm2 illumination in air.It is indicated that ReO3 can be used as an effective buffer layer to enhance the polymer bulk heterojunction(BHJ) photovoltaic cell efficiency.