We investigated the effects of poly(3, 4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films treated with methoxyethanol (ME) on the performance of polymer solar cells, and the effects were compared with the PEDOT:PSS films treated with dimethyl sulfoxide (DMSO). In particular, a correlation between the performance parameters of polymer solar cells and changes in the conductivity, surface morphology, and work function of treated PEDOT:PSS was investigated as a function of an added ME and DMSO ratio. The enhanced conductivity of the treated PEDOT:PSS improved the short circuit current and reduced the series resistance of solar cells. While the enhanced conductivity and surface roughness of the treated PEDOT:PSS also induced the large leakage current and sacrificed the device FF. The open circuit voltage was almost constant, although the slightly reduced voltage was observed. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.