Tailoring molecular orientation to enhance photocurrent and fill factor in green-solvent processed organic solar cells

Abstract

The transition to non-halogenated solvents is a critical barrier to the scalable manufacturing of organic solar cells (OSCs). This work reveals distinct, thickness-dependent failure mechanisms in PTB7-Th:BTPV-4F-eC9 blends processed from benign solvents. We provide a definitive framework showing that in thin (80 nm) films, performance is dictated by molecular crystallization and orientation, which are directly controlled by the solvent and limit the short-circuit current. As the film thickness increases to a more commercially relevant 125 nm, a different mechanism dominates: performance loss is primarily driven by a reduction in the NFA absorption peak, which throttles charge generation while recombination rates remain unaffected. Crucially, we demonstrate that these limitations are not fundamental. We introduce a potent solid additive strategy that systematically overcomes both bottlenecks, simultaneously restoring favorable molecular orientation and NFA self-aggregation. This provides a clear mechanistic framework and a powerful new tool for designing high-efficiency, thickness-tolerant OSCs for scalable “green” manufacturing.