Towards optimization of device performance in conjugated polymer photovoltaics: Charge generation, transfer and transport in poly(p-phenylene-vinylene) polymer heterojunctions

We fabricate photovoltaics comprised layers and blends of a hole-transporting derivative of poly(p-phenylene-vinylene) with a variety of electron-transporters: titanium dioxide, a cyano-substituted PPV, and a fullerene derivative (PCBM) to enhance device performance. Photovoltaic device characterization is combined with time-resolved and steady-state photoluminescence to understand the nature of the excited state and its effect upon device performance. We find that morphological differences, such as chain conformation or domain size, often overshadow the effect of charge transfer, so that device performance is not necessarily correlated with rapid decay times. Exciton generation is found to be a similarly important factor in most devices. These results provide insight into non-optimized device morphologies.