Electrodes made of vertically-aligned ZnO nanorods (NRs) have been prepared and analyzed in dye sensitized solar cells (DSC). We report a 20% power conversion efficiency increase during the first hours of solar cell testing at 1000 W m⁻² (AM 1.5). The latter has been attributed to the physisorption/chemisorption of the N-719 dye on the ZnO NRs induced by UV-light irradiation. The ZnO NRs were grown by the hydrothermal method for 6 h obtaining a ZnO layer thickness of about 1.8 μm. The highest solar cell efficiency obtained was 0.69% after UV light irradiation (at 72 °C, 0.63 V, 2.85 mA cm⁻², 0.39 FF). The effect of UV light has been monitored by UV-VIS, IV-curves and IPCE analyses with time, and has been related to the solar cell performance.