Initial temperature regulation of precursor solution assembly enables high performance organic solar cells

Abstract

A critical challenge in optimizing the morphology of organic solar cell active layers lies in achieving precise control over the pre-aggregation behavior of donors and acceptors using simple and solution-processable parameters to construct an ideal microstructure. To address this issue, this study proposes a precursor-solution assembly strategy based on tuning the initial temperature of the blended solution to optimize the microstructure of PM6:L8-BO binary organic solar cell active layers. The results demonstrate that a moderate initial temperature (60 °C) effectively regulates the pre-aggregation behaviour of the donor and acceptor, leading to an active layer with a smoother surface, more favourable phase separation, and better-coordinated molecular packing. Consequently, exciton dissociation and charge transport are facilitated, while recombination losses are suppressed. Ultimately, the PM6:L8-BO binary device achieves a power conversion efficiency of 20.23%, with significant improvements in both short-circuit current density and fill factor. Importantly, this strategy shows good universality, yielding optimal PCEs of 20.59% and 17.94% in both D18:L8-BO and PM6:Y6 devices with 60 °C coating, respectively. This work establishes a clear structure–property relationship linking initial temperature, pre-aggregation behaviour, thin-film microstructure, and device performance, thereby providing a novel strategy for morphology control and process optimization of high-performance organic solar cells.