Device simulation of low-band gap polymer solar cells: Influence of electron-hole pair dissociation and decay rates on open-circuit voltage

We simulated the performance of recently developed highly efficient bulk heterojunction photovoltaic cells with poly [N-$9″$-hepta-decanyl-2,7-carbazole-alt-5,5-(⁠$4′,7′$-di-2-thienyl-$2′,1′,3′$-benzothiadiazole)] as the donor and [6,6]-phenyl $C70$-butyric acid methyl ester as the acceptor, using a device model. The simulated current-voltage curve is in excellent agreement with the experiment. This enables us to analyze how microscopic processes of excitons and charges govern the device performance. The influence of dissociation rate and decay rate of photoinduced electron-hole pairs on the open-circuit voltage $VOC$ is investigated. It is shown that a high dissociation rate relative to decay rate will lead to enhanced $VOC$⁠.