Efficient bulk-heterojunction (BHJ) (regioregular poly (3-hexylthiophene) (P3HT): (6, 6)-phenyl C-61 butyric acid methyl ester (PCBM)) solar cells were fabricated with molybdenum trioxide (MoO3) and copper phthalocyanine (CuPc) as buffer layers. The insertion of MoO3 layer was found to be critical to the device performance, effectively extracting holes to prevent the exciton quenching and reducing the interfacial resistance because of alignment of energy levels. The introduction of CuPc buffer layer was observed to be ameliorative for device performance, further enlarging the visible absorption spectra range of the devices. The effect of the MoO3 and CuPc layer thickness on device performance was studied. The optimized thickness was achieved when MoO3 layer was 12 nm and CuPc layer was 6 nm, resulting in optimized power conversion efficiency (PCE) of 3.76% under AM1.5G 100 mW/cm(2) illumination. (C) 2011 Elsevier B.V. All rights reserved.