Solar cells based on a poly (p-phenylene vinylene) (PPV) derivative and zinc oxide nanoparticles can reach a power conversion efficiency of 1.6%. The transport of electrons and holes in these promising devices is characterized and it is found that the electron mobility is equal to 2.8 x 10(-9) m(2) V-1 s(-1), whereas the hole mobility amounts to 5.5 x 10(-10) m(2) V-1 s(-1). By modeling the current-voltage characteristics under illumination it is found that the performance of PPV/zinc oxide solar cells is limited by the charge-carrier mobilities. Subsequently, how to further improve the efficiency is discussed.