Nucleation driving force-controlled fibril network formation using a non-halogenated solvent enables polythiophene solar cells with over 18% efficiency†

Abstract

Polythiophenes are the most promising electron donors for organic solar cells (OSCs) in large-scale manufacturing owing to their simple chemical structures and low production costs. However, the efficiency of polythiophene solar cells is largely limited because of the difficulty in morphology optimization. Herein, we report the construction of a refined fibril network structure in polythiophene:non-fullerene acceptor blends based on the classical nucleation theory. By screening solvents for polythiophene to obtain an appropriate nucleation driving force while ensuring that the non-fullerene acceptor does not over-crystallize, a refined crystalline fibril network morphology was obtained in the blend consisting of a structurally simple polythiophene P5TCN-HD and a non-fullerene acceptor. This optimal morphology improved exciton dissociation and charge transport, thereby endowing 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. Notably, these results were achieved using toluene as the solvent, which is a common non-halogenated and environmentally benign solvent. Moreover, the crucial impact of solvent quality on the formation of the fibril network structure was revealed, 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 environmentally benign processing, driving the industrialization of OSCs.