In this work, we investigate in great detail the silicon nanowire (SiNW)/poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid solar cells (SCs). Because of the light-trapping effect, SiNW/PEDOT:PSS SCs absorb more light than planar Si/PEDOT:PSS SCs. Also, the light absorption increases with the length of the SiNWs. However, the SiNW's length is not the only factor that influences the SCs. Thus the SiNW/PEDOT:PSS SCs with the shortest wire length of 0.37 mu m have the best performance in terms of the highest power conversion efficiency of 8.40%, the largest short circuit current density of 24.24 mA cm(-2), and open circuit voltage of 0.532 V, compared with the SCs of other wire lengths. The reasons are two-fold. First, long SiNWs tend to aggregate at the top portion, making the infiltration of PEDOT:PSS difficult, so the coverage of PEDOT:PSS on the SiNWs is not complete. Second, the increase of SiNW length greatly reduces the minority-carrier lifetime. Our investigation will help develop SiNW SCs with improved performance. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.