Halogen‐Free [Formula: see text] ‐Conjugated Polymers Based on Thienobenzobisthiazole for Efficient Nonfullerene Organic Solar Cells: Rational Design for Achieving High Backbone Order and High Solubility

In [Formula: see text] ‐conjugated polymers, a highly ordered backbone structure and solubility are always in a trade‐off relationship that must be overcome to realize highly efficient and solution‐processable organic photovoltaics (OPVs). Here, it is shown that a [Formula: see text] ‐conjugated polymer based on a novel thiazole‐fused ring, thieno[2′,3′:5,6]benzo[1,2‐d:4,3‐d′]bisthiazole (TBTz) achieves both high backbone order and high solubility due to the structural feature of TBTz such as the noncovalent interlocking of the thiazole moiety, the rigid and bent‐shaped structure, and the fused alkylthiophene ring. Furthermore, based on the electron‐deficient nature of these thiazole‐fused rings, the polymer exhibits deep HOMO energy levels, which lead to high open‐circuit voltages (V (OC)s) in OPV cells, even without halogen substituents that are commonly introduced into high‐performance polymers. As a result, when the polymer is combined with a typical nonfullerene acceptor Y6, power conversion efficiencies of reaching 16% and V (OC)s of more than 0.84 V are observed, both of which are among the top values reported so far for “halogen‐free” polymers. This study will serve as an important reference for designing [Formula: see text] ‐conjugated polymers to achieve highly efficient and solution‐processable OPVs.