Nucleation driving force-controlled fibril network formation enables polythiophene solar cells with exceeding 18% efficiency from non-halogenated solvent

Abstract

Polythiophenes are the most promising electron donors for organic solar cells (OSCs) in large-scale manufacturing due to their simple chemical structures and low production cost. However, the efficiency of polythiophene solar cells is largely limited by the difficulty in morphology optimization. Herein, we report the construction of refined fibril network structure in polythiophene:non-fullerene acceptor blends based on Classical Nucleation Theory. By screening solvents for polythiophene to obtain appropriate nucleation driving force while ensuring that the non-fullerene acceptor does not over-crystallize, a refined crystalline fibril network morphology in the blend consisting of a structurally simple polythiophene P5TCN-HD and non-fullerene acceptor was obtained. This optimal morphology improves exciton dissociation and charge transport, thereby endowed the solar cells with an unprecedented power conversion efficiency of 18.12% and a fill factor of 79.17%, marking new breakthroughs for polythiophene-based OSCs. Importantly, these successes were achieved from toluene, a common non-halogenated and environmental benign solvent. Moreover, we revealed the crucial impact of solvent quality on the formation of fibril network structure, offering valuable insights for optimizing the morphology of polythiophene systems. This underscores the promising prospect of polythiophenes in developing high-efficiency yet low-cost OSCs via environmental benign processing, which will drive the industrialization of OSCs.