Halogenated Volatile Additive Strategy for Regulating Crystallization Kinetics and Enabling 20.40% Efficiency Polymer Solar Cells with Low Non-Radiative Recombination Energy Loss

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