Highly efficient non-fullerene organic solar cells enabled by a delayed processing method using a non-halogenated solvent
The use of non-halogenated solvents is one of important requirements for large-scale industry production of polymer solar cells (PSCs). However, the current high-performance PSCs are mostly obtained using the halogenated solvents to ensure good solubility and morphology. In this work, we report high-performance PSCs processed using halogen-free solvent (toluene), reaching an efficiency of 17.33%, which, to the best of our knowledge, is the highest value reported for PSCs processed from non-halogenated solvents. Importantly, we show a novel aggregation or “aging” process of the non-fullerene acceptor in the toluene solvent, which can be used to fine-tune the crystal size of non-fullerene acceptor. As a result, we achieve an optimized nano-fibril like morphology of PM6:BTP-BO-4Cl by delaying the processing time. This is conducive to the charge dissociation and transport, and thus the greatly improved device performance. This method is expected to be investigated further and applied to other PSC systems toward the precise morphology optimization and performance improvements in the future.