Role of Interface Energetics and Off-diagonal Disorder in Bulk Heterojunction Organic Solar Cells

Organic Solar Cells (OSCs) have been extensively studied regarding the impact of morphology and energetic disorder on power conversion efficiency (PCE). The impact of energetic disorder is well understood but the effect of disorder in molecular coupling (off-diagonal) and energetic disorder at the interface still needs investigation. We present a kinetic Monte Carlo (kMC) model to study the role of interface energetics and off-diagonal disorder on solar cell performance. We first analyze the impact of different energetic disorder at the acceptor(A)-donor(D) interface on the device performance. Our results reveal that the interface properties control the Voc and efficiency. For higher interface disorder, recombination increases and the Voc is reduced. We further demonstrate the impact of variable off-diagonal disorder at fixed interface disorder on the device. The results show that at higher off-diagonal disorder, recombination, as well as Voc, is reduced. The presented results allow a better understanding of the importance of the structural order at the interface for OSCs.