We have incorporated silicon nanoparticles (Si-nps) into organic-inorganic hybrid solar cells in place of the chalcogenide nanocrystals that are commonly employed in such devices. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and phenyl-C-61-butyric acid methyl ester (PCBM) were employed as hole and electron transport layers, respectively. We used transmission electron microscopy, Raman spectroscopy, and ultraviolet-visible spectroscopy to fully characterize the Si-nps and relate their characteristics to the performance of the hybrid solar cells. We show that the open circuit voltage (V-OC) was largely dependent on the size and amorphous volume fraction of Si-nps. Our findings imply that the amorphous phase and small size of Si-nps produce band gap widening that increases the V-OC when coupled with PCBM as acceptor. The maximum V-OC was up to 0.634 V in a hybrid device with 5.7 nm Si-nps. (C) 2013 Elsevier B. V. All rights reserved.