Fullerene concentration dependent bimolecular recombination in organic photovoltaic films

Organic photovoltaic devices made of a solution processed small molecule and a fullerene show a decrease in short circuit current with decreasing fullerene amounts. Transient absorption experiments show that the rate of bimolecular recombination increases as the system is deprived of fullerene. A simple expression for the bimolecular recombination coefficient derived by accounting for intrinsic carrier generation reproduces the observed behavior.