Polymer-like tetramer acceptor enables stable and 19.75% efficiency binary organic solar cells
Jianxiao Wang, Cheng Sun, Yonghai Li, Fuzhen Bi, Huanxiang Jiang, Chunming Yang, Xichang Bao, Junhao Chu
Abstract
Limited by large batch differences and inferior polymerization degree of current polymer acceptors, the potential high efficiency and stability advantages of all-polymer solar cells (all-PSCs) cannot be fully utilized. Alternatively, largely π-extended and structurally definite oligomer acceptors are effective strategies to realize the overall performance of polymer acceptors. Herein, we report a linear tetramer acceptor namely 4Y-BO with identical molecular skeleton and comparable molecular-weight relative to the control polymer acceptor PY-BO. The structurally definite tetramer shows refined film-forming kinetics and improved molecular ordering, offering uniform crystallinity with polymer donor and hence well-defined fibrous heterojunction textures. Encouragingly, the PM6:4Y-BO devices achieve an efficiency up to 19.75% (certified efficiency:19.58%), largely surpassing that of the control PM6:PY-BO device (15.66%) and ranks the highest among solar cells based on oligomer and polymer acceptors. More noticeably, thermal stability, photostability and mechanical flexibility are collectively enhanced for PM6:4Y-BO devices. Our study provides an important approach for fabricating high performance and stable organic photovoltaics.