Modification of the Electron‐Deficient Core on Unfused‐Ring Acceptors Enabling High Open‐Circuit Voltage of Organic Solar Cells

Unfused‐ring acceptors with different electron‐deficient central units, dithieno[3,2‐f:2′,3′‐h]quinoxaline (KS40) and dithieno[3,2‐e:2′,3′‐g]‐2,1,3‐benzoxadiazole (KS41) are synthesized and characterized. When blended with PM6, KS40 with a weaker electron‐accepting quinoxaline exhibits a much higher open‐circuit voltage (VOC) of 0.945 V. As a result, the KS40‐based device achieves a power conversion efficiency (PCE) of 12.2%. PM6:KS41‐based devices, in contrast, afford improved charge mobilities as well as suppressed recombination behavior, which eventually leads to an improvement in the fill factor (72.4%). Consequently, the device is able to achieve a PCE of 11.6%.