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 (Eloss ) of 0.57 eV, accompanied by a high open-circuit voltage (Voc ) 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.