Post‐Treatment‐Free Main Chain Donor and Side Chain Acceptor (D‐s‐A) Copolymer for Efficient Nonfullerene Solar Cells with a Small Voltage Loss

Main chain donor and side chain acceptor (D‐ s ‐A) copolymers are an important branch of the D–A copolymer family. However, the development of D‐ s ‐A copolymers significantly falls behind the alternative D–A copolymers, especially for organic solar cells, because a breakthrough in device performance is not yet obtained with a reported power conversion efficiency (PCE) of 2%–4%. Herein, a newly developed D‐ s ‐A copolymer PDRCNBDT , bearing 2‐(1, 1‐dicyanomethylene) rhodanine pendant group as the donor material, delivers a high PCE of 5.3% for nonfullerene solar cells. To the best of our knowledge, this is the best value reported for D‐ s ‐A copolymers to date. The improved PCE is observed to be associated with a very small energy loss ( E loss ) of 0.57 eV, accompanied by a high open‐circuit voltage ( V oc ) of 1.015 eV. It is important to note that this efficient D‐ s ‐A copolymer is employed in organic solar cells (OSCs), free of additive and annealing treatments.