Role of the interface and extraction layer energetics in organic solar cells

Interface engineering plays an important role in performance improvement for bulk-heterojunction organic solar cells (OSCs). The charge carrier dynamics and energetic landscape at the donor:acceptor (D:A) interface can strongly differ from the bulk of the active layer. This is particularly crucial for the device performance when the interface is strongly disordered or nanostructured. In this work, we present a kinetic Monte Carlo (kMC) study to clarify the role of the disorder at the D:A interface and the interface between the photoactive layer and the extraction layer on the performance of bulk-heterojunction OSCs. We parametrize the material parameters for a moderately efficient OSC. Our results demonstrate that the disorder at the D:A interface especially tailors the photocurrent and fill factor, while the disorder at the extraction layer mainly controls the open-circuit voltage. The D:A interface plays the dominant role in device performance and needs to be controlled to achieve efficient OSCs. Furthermore, we show that losses due to the interface disorder can be partially restored in the presence of energy cascades by mixed phases within the interface region.