Chain conformation and aggregation structure regulation of an efficient acceptor–acceptor type photovoltaic polymer

Abstract

In recent years, donor copolymers with an acceptor₁–acceptor₂ (A₁–A₂) structure have attracted great attention in the field of organic solar cells (OSCs). Compared to the traditional D–A type donor, the double acceptor type polymer not only expands photovoltaic donor diversity, but also further deepens the energy level due to the stronger electron affinity. However, the general A₁–A₂ structure with non-linear polymeric conformations limited the efficient charge transportation and photovoltaic performance. Herein, fluorine substituted benzotriazole (FBTZ) was selected as an acceptor₁ (A₁) unit and copolymerized with a more planar 1,3-bis(thiophen-2-yl) benzodithiophene-4,8-dione (BDD) as an acceptor₂ (A₂) unit to construct two polymer donors P94 and P95 with an A₁–A₂ structure. The two copolymer donors show a deep-lying energy level and the P95 film exhibited a higher hole mobility of up to 1.0 × 10⁻³ cm² V⁻¹ s⁻¹. Interestingly, although P94 and P95 had the same main chains, it was found that less steric hindrance induced less H-aggregation and more linear polymer conformations. Correspondingly, the dominating J-aggregation and linear conformation of P95 exhibited a better power conversion efficiency of 13.51%. To the best of our knowledge, it is the highest efficiency of OSCs based on A₁–A₂ type copolymer donors in recent years. Therefore, the development of an A₁–A₂ type donor has great potential in constructing efficient photovoltaic donors.