Pentacene/fullerene (C60) heterojunction solar cells: Device performance and degradation mechanisms

We demonstrate power conversion efficiencies of 1.5% from molecular photovoltaic devices based on bilayer pentacene/fullerene heterojunctions under 1 sun AM1.5G simulated irradiation. Importantly, we demonstrate the independence of the device performance on active area in the range 0.05–0.65 cm2, a critical consideration for future scaling up to manufacture. A degradation study under constant solar illumination shows two parallel mechanisms for degradation; a photooxidation resulting in a drop of the generated photocurrent, and a UV annealing effect reducing the fill factor, both of which can be eliminated by careful choice of analysis conditions.