Enabling Highly Efficient and Thermal‐Stable Polymer Solar Cells through Semi‐Alloy Acceptors Composed of a Hinge‐Like Dimer: A Versatile Doping Protocol

Abstract The simultaneous improvement of power conversion efficiency (PCE) and thermal stability is a critical scientific challenge in advancing the commercial applications of polymer solar cells. To address this challenge, a dumbbell‐shaped dimeric acceptor, DT19, is successfully designed and synthesized. It is incorporated as a third component into the PM1:BTP‐eC9 system. This ternary strategy demonstrates a synergistic enhancement of the PCE and thermal stability of the host binary system. In particular, the PM1:BTP‐eC9:DT19 system maintains a PCE of over 90% even after heating at 120 °C for 200 h. Additionally, the dimer‐doping ternary strategy exhibits excellent generality for the other four Y‐series systems and outperforms ternary systems containing alloy‐like acceptors in terms of thermal stability. It is because DT19, with its hinge‐like structure, can form a semi‐alloy acceptor with the host acceptor, leading to strong interchain entanglement with the polymer donor, thus overcoming phase separation and excessive aggregation under thermal stress. This new type of dimeric material, which can synergistically enhance the device efficiency and thermal stability of active layers, presents promising application prospects.