Asymmetric Fluorene‐Based Fused‐Ring Molecules Acceptors for Fullerene‐Free Organic Solar Cells

Abstract

Asymmetric fluorene‐based fused‐ring molecules acceptors 2,2′‐((2Z,2′Z)‐(((11,11‐dioctyl‐5,5‐dioxido‐11H‐benzo[b]fluoreno[2,3‐d]thiophene‐3,9‐diyl)bis(3‐octylthiophene‐5,2‐diyl))‐bis(methaneylylidene))bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile [BTOFIC] and 2,2′‐((2Z,2′Z)‐((5,5′‐(11,11‐dioctyl‐11H‐benzo[b]fluoreno[2,3‐d]thiophene‐3,9‐diyl)bis(3‐octylthiophene‐5,2‐diyl))bis(methanylylidene))‐bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diyl‐idene))dimalononitrile [BTFIC] are synthesized. BTOFIC and BTFIC are easily soluble in common organic solvents. The highest occupied molecular orbital energy levels, the lowest unoccupied molecular orbital energy levels, and the bandgaps (Egs) of BTOFIC and BTFIC are −5.91, −3.87, and 2.04 eV and −5.72, −3.81, and 1.91 eV, respectively. BTOFIC and BTFIC show the maximum absorption peak (λmax) at 548 and 648 nm and a strong shoulder peak at 592 and 576 nm in film, and the optical bandgaps of 1.87 and 1.81 eV, respectively. The organic solar cells (OSCs) fabricated with poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)] [PTB7‐Th]:BTOFIC and PTB7‐Th:BTFIC show a power conversion efficiency of 3.31% and 5.35%, respectively. In this research, it is revealed that BTOFIC and BTFIC can be potential asymmetric non‐fullerene acceptors for further development of OSCs.