Conditions for efficient exciton dissociation in non-fullerene organic solar cells

Abstract

The minimum driving force strategy is usually applied to promote the exciton dissociation in organic solar cells (OSCs) without significant loss of open-circuit voltage. Despite the advances on this topic, the correlation between driving force and efficient free charge generation remains unclear. To answer this question, we employ a kinetic approach to study the charge separation in ten different donor/acceptor (D/A) blends [4] using non-fullerene acceptors. The model takes into account disorder effects in the driving forces (ΔG) and electronic coupling (β) to obtain the transitions rates (k) from the Marcus/Hush theory. We demonstrate that our model successfully predicts the measured photoluminescence quenching efficiency for acceptor excitation in those blends (Fig. 4). In addition, we show that a relationship derived from our approach (Eb,CT < ΔGHT) can successfully predict the quenching efficiency. The model also revealed the fundamental role played by the exciton lifetime to enhance the charge generation process. Our results demonstrate a comprehensive picture of the exciton dissociation at the heterojunction. In addition, our observations suggest guidelines for a rational material design aiming the optimization of OSCs.