We investigated the influence of glycerol doping to poly (3,4-ethylenedioxy-thiophene): poly(styrene sulfonate) (PEDOT:PSS) on the power conversion efficiency (PCE) of the bulk heterojunction photovoltaic cells using poly (3-hexylthiophene) and phenyl-C61-butyric acid methyl ester. In particular, a correlation between PCE and changes in the conductivity, surface morphology, contact properties, and work function of glycerol-doped PEDOT:PSS(G-PEDOT:PSS) was investigated as a function of an added glycerol ratio. The PCE was increased from 2.5 to 3.3% by using the optimum glycerol doping ratio. It is believed that the improved PCE of the photovoltaics is possibly due to the increased short-circuit current from the enhanced hole carrying ability as well as the enlarged contact area of the doped buffer layer. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3196243] All rights reserved.