A halogenated volatile additive strategy for regulating crystallization kinetics and enabling 20.40% efficiency polymer solar cells with low non-radiative recombination energy loss

Abstract

Halogenated volatile additives play an important role in well regulating the blend morphology in polymer solar cells (PSCs). However, the mismatched crystallization rate between the donor and acceptor often leads to difficulties in realizing a desirable morphology, further resulting in non-radiative recombination energy loss (ΔE_non-rad). Herein, a series of halogenated volatile additives of 1-fluoro-3,5-dimethoxybenzene (F-DMB), 1-chloro-3,5-dimethoxybenzene (Cl-DMB), 1-bromo-3,5-dimethoxybenzene (Br-DMB) and 1-iodo-3,5-dimethoxybenzene (I-DMB) have been designed to optimize the interaction with donors and acceptors, thereby regulating the crystallization kinetics, improving morphology quality and reducing ΔE_non-rad. As the weight of the halogen atoms of additives increased, the promoting effect of additives on PM6 strengthened gradually, thus shortening the crystallization time. However, such a promoting effect on L8-BO weakened, resulting in a longer crystallization time. Therefore, this strategy made the crystallization time ratio approach unity with a more balanced crystallization behavior. Due to the well-regulated crystallization kinetics and optimized intermolecular aggregation, an optimal morphology with suppressed energy disorder and ΔE_non-rad was realized. The I-DMB-treated PSCs exhibited the champion power conversion efficiency (PCE) of 20.40% and a minimized ΔE_non-rad of 0.189 eV. This work offers valuable insights into how to utilize volatile additives for regulating crystallization kinetics and optimizing a desirable morphology of PSCs for further improving photovoltaic performance.