Efficient and Nonhalogenated Solvent-Processed Organic Solar Cells Enabled by Conjugated Donor–Acceptor Block Copolymers Containing the Same Benzodithiophene Unit

Organic solar cells (OSCs) based on conjugated block copolymers (CBCs) have gained considerable attention owing to their simple one-pot solution process. However, their power conversion efficiencies (PCEs) require significant improvement. Furthermore, the majority of efficient CBC-based OSCs are processed using environmentally toxic halogenated solvents. Herein, we develop a new CBC (PBDB-T-b-PY5BDT) and demonstrate efficient and stable OSCs achieved by a halogen-free solution process. We design a (D1-A1)-b-(D1-A2)-type CBC (PBDB-T-b-PY5BDT) that shares the same benzodithiophene (BDT) units in donor and acceptor blocks. This alleviates unfavorable molecular interactions between the blocks at their interfaces. The PBDB-T-b-PY5BDT-based devices exhibit a high PCE (10.55%), and they show good mechanical, thermal, and storage stabilities. Importantly, we discuss the potential of our OSCs by preparing two different control systems: one based on a binary polymer blend (PBDB-T:PY5BDT) and another based on a conjugated random copolymer (CRC, PBDB-T-r-PY5BDT). We demonstrate that the photovoltaic performance, device stability, and mechanical robustness of the CBC-based OSCs exceed those of the binary all-polymer solar cells and CRC-based OSCs.