The influence of the Cd-to-Se precursor ratio during the synthesis of CdSe nanoparticles (nc-CdSe) on the efficiency of solar cells made from semiconducting polymer/nanocrystal-blends (hybrid solar cells) was investigated. In these hybrid solar cells regioregular poly-(3-hexylthiophene 2,5 diyl) (P3HT) was used as the electron donor material while the acceptor was established by CdSe nanocrystals prepared via colloidal synthesis. Furthermore, the influence of the nc-CdSe-to-P3HT ratio in the semiconductor blend on the solar cell efficiency was investigated. CdSe:P3HT ratios of 8:1 to 10:1 were found to give the best results concerning the overall device performance as derived from current–voltage characterization. These findings were correlated with structural investigations of the active layer by means of atomic force microscopy (tapping mode AFM). Furthermore, the external quantum efficiency (EQE) of the hybrid solar cells was determined and also used to estimate the short circuit current density Jsc under standardized solar irradiation. The Jsc values from the EQE measurements were compared to the values obtained from the IV curves. Differences in these values could be explained by an intensity-dependent influence of trap states.