Efficient bulk-heterojunction (BHJ) polymer solar cells (PSCs) based on poly (3-hexylthiophene) (P3HT): indene-C-60 bisadduct (ICBA) were fabricated with lithium fluoride (LiF) as electron collecting buffer layer and UV-ozone (UVO) treated molybdenum trioxide (MoO3) as hole collecting buffer layer. LiF is observed to be critical for the device performance, significantly enhancing the fill factor (FF) and the efficiency compared to the device without LiF layer. MoO3 layer is also critical to the device performance, efficiently extracting holes to prevent the exciton quenching and reducing the interfacial resistance because of alignment of energy band. After UVO treatment on MoO3 film, its surface morphology, transmittance and film quality can be improved, therefore, it is beneficial to the performance of the PSCs. The optimal thickness of MoO3 and UVO treatment time on MoO3 was 12 nm and 15 min, respectively. Based on these optimal parameters, a power conversion efficiency (PCE) of 6.43% was obtained under AM1.5G 100 mW/cm(2) illumination. (C) 2012 Elsevier B.V. All rights reserved.