Electron-deficient diketone unit engineering for non-fused ring acceptors enabling over 13% efficiency in organic solar cells

Different from the commonly studied non-fullerene electron acceptors with large fused backbone architecture and tedious synthesis steps, non-fused ring electron acceptors are attractive for organic solar cells (OSC) due to their simple synthesis and comparable device performance. However, it is key to choose appropriate building blocks for constructing non-fused ring electron acceptors to achieve high-performance OSCs. Herein, two simple non-fused ring electron acceptors, TPDC-4F and BTIC-4F, which possess the same terminals and 4H-cyclopenta[1,2-b:5,4-b ']dithiophene unit coupled with different electron-deficient diketone central units, are synthesized. TPDC-4F with a thieno[3,4-c]pyrrole-4,6-dione core exhibits a smaller optical bandgap of 1.42 eV, downshifted lowest unoccupied molecular orbital energy levels, higher electron mobility, and enhanced molecular packing order in neat thin films as compared to BTIC-4F with a 2,2 '-bithiophene-3,3 '-dicarboxyimide core. As a result, the OSC based on TPDC-4F with stronger molecular packing yielded a high power conversion efficiency (PCE) of 13.35% with a V-oc of 0.852 V, which is one of the best values ever reported in non-fused ring electron acceptors-based binary OSCs with V-oc over 0.85 V, and is better than that of OSC based on the BTIC-4F with weaker molecular stacking (PCE = 12.04%). This work demonstrates the application of electron-deficient diketone units in efficient non-fused ring electron acceptors and provides molecular design guidance for high-performance OSCs.