It has been studied that the effect of different electron transporting materials, including 2-(4-biphenyl)-5-(4-tert-butylphenyl)1,3,4-oxidiazole (PBD), tris-8-hydroxy-quinolinato aluminum and Bis[2-(2-benzothiazoly) phenolato]zinc(II) on the properties of solar cells based on poly(3-hexylthiophene) and [6,6]-phenyl-C(61)-buytyric add methyl ester composites. The results suggest that the insertion of electron transporting layers (EFL) can improve the open circuit voltage (Voc) and power conversion efficiency (PCE) of the polymer solar cells. And the effect of thickness of the three ETL has also been investigated. The cell with a PBD layer exhibits an enhanced Voc by 0.16 V and the highest PCE, which is 1.6 times that of the cell without ETL The improved performance is due to the increased built-in potential in the interface between the active layer and Al electrode. (c) 2011 Elsevier B.V. All rights reserved.