The authors have demonstrated and estimated the extension of active region in P3HT:PCBM solar photovoltaics due to the increase in the conductivity of PEDOT:PSS. For the polymer photovoltaics with a crossbar-type electrode geometry, the excess photogenerated carriers outside the nominal active region have contributed the measured photocurrent and thus affected the derived power conversion efficiency. In this work, glycerol and dimethyl-sulfoxide were, respectively, incorporated into PEDOT: PSS to increase the conductivity and therefore improve the performance of the devices. The method of restrictively illuminating the partially shielded device was introduced to eliminate the excess photocurrent and well define the real active region. The extension of active area was also figured out by fitting the short-circuit current of shielded device. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3437506]