Planar hybrid heterojunctions were built with poly 3-octylthiophene (P3OT) and chemical bath-deposited cadmium sulfide (CdS) thin films on a conductive glass substrate. The organic material, P3OT, acts as a light absorber and the inorganic one, CdS, as the electron acceptor. Two types of CdS films had been used: one is as-deposited and the other doped with HgO(2). Heterojunctions were formed by casting a chemically synthesized P3OT solution onto CdS films. The P3OT film thickness was also varied for heterojunction studies. Current vs. potential (I-V) characterizations under dark and illumination conditions were performed for the P3OT/CdS heterojunctions under 88 mW/cm(2) irradiance level, which show photovoltaic effect with different open circuit voltage (V(OC)) levels, being as high as 1V for some devices. A parametric analysis of I-V curves details the effect of CdS resistivity and P3OT film thickness on series and shunt resistance of the heterojunctions. (c) 2006 Elsevier B.V. All rights reserved.