We report on improved stability of poly(3-hexylthiopene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester bulk heterojunction solar cells using an indium tin oxide (ITO) anode and an indium metal cathode. Except for the ITO anode the devices are fabricated, stored, and tested entirely in air without encapsulation, exhibiting less than 10% loss in power conversion efficiency after 200 days. X-ray photoelectron spectroscopy shows that this improvement in ambient stability is correlated with the diffusion of indium from the cathode into the active polymer. The In oxidizes presumably resulting in a reduction in P3HT polymer chain degradation.