Hybrid Solar Cells (HSC) applying Nb-TiO2 in direct contact with a conducting organic polymer, MEH-PPV, show higher stability than the bare TiO2-based HSC when analyzed under inert atmosphere conditions. IPCE analyses revealed that inert atmospheres affect directly the semiconductor oxide in the first stages of the analyses but photovoltaic performance stabilizes after several hours. A 20 wt% Nb-doped TiO2 presented the highest stability and photovoltaic properties. The behavior has been attributed to the solubility limit of Nb within the TiO2 beyond 20 wt% doping level where the co-existence of NbO2 is observed. The HSCs were analyzed under controlled N-2 atmosphere and 1000 W/m(2) (AM 1.5) irradiation. (C) 2010 Elsevier B.V. All rights reserved.