Modulation of Phase Separation Morphology by Configuration Engineering in Bulk Heterojunction Organic Solar Cells

For bulk-heterojunction organic solar cells (OSCs), molecular structure design to control molecular stacking is crucial to obtain ideally phase-separated morphology and high device performance. Herein, the investigation focuses on two polythiophene-quinoxaline (PTQ) derivatives (PTQ8 and PTQ10) blended with Y6, utilizing coarse-grained molecular dynamics simulations based on the Lennard-Jones static potential (LJSP) method. The study reveals that the diminished photovoltaic efficiencies of PTQ8:Y6 blends, compared to PTQ10:Y6 blends, are not solely attributed to reduced driving forces. The introduction of fluorine-substituted sites in the thiophene group of PTQ polymer is identified as a significant factor. This alteration causes PTQ polymers in PTQ8:Y6 blends to coil, compromising the crystalline structure. PTQ8's bifluorine group induces a repulsive effect on the quinoxaline group, leading to a coiled-chain structure that hinders chain stacking. Conversely, PTQ10 exhibits a straighter chain conformation. Additionally, PTQ8's high solubility in chloroform prevents effective aggregation, further impeding suitable morphology formation. Coarse-grained simulations employing LJSP prove effective in precisely exploring the morphology of OSCs, offering crucial insights for materials in this field. This study explores the impact of blending PTQ8/PTQ10 with Y6 using CGMD. The diminished photovoltaic efficiencies of PTQ8:Y6 blends compared to PTQ10:Y6 blends are not solely attributed to reduced driving forces. The incorporation of fluorine-substituted sites within the PTQ emerges as a significant factor, inducing coiling within PTQ8 and consequently compromising the crystalline structure within the blends.image (c) 2024 WILEY-VCH GmbH