The aim of this work has been to study the influence of modified hole-extraction layers on the performance of organic solar cells (OSCs) based on blends of poly (3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester. The hole-extraction layers consist of poly (3,4-ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) doped with different concentrations of bromine. Compared with pristine OSC without adding bromine to the hole-extraction layer, the bromine-doped OSCs show a 49% increase in the power conversion efficiency (from 2.12 to 3.16%), which could be attributed to the increase of electrical and optical properties of PEDOT:PSS films after the addition of bromine. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 125128, 2012