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

Abstract

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.