Efficient ternary organic solar cells with BT-rhodanine-based nonfullerene acceptors in a PM6:Y6-BO blend

A series of benzothiadiazole (BT)-rhodanine-based nonfullerene acceptors (NFAs) were designed and synthesized. These BT-rhodanine-based NFAs were composed of BT as a central core with a 3-octylthienothiohene pi-bridge and two different rhodanine end groups (BT-rho for octylrhodanine and BT-rhoCN for dicyano-octylrhodanine end groups). The highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels were -5.53/-3.78 eV for a BT-rho film and -5.63/-3.90 eV for a BT-rhoCN film. The strong electron-withdrawing dicyano-octylrhodanine end group of BT-rhoCN downshifted the HOMO and LUMO levels by similar to 0.1 eV compared with those of BT-rho. The 10% BT-rho in a PM6:Y6-BO ternary organic solar cell exhibit a maximum power conversion efficiency (PCE) of 16.17% with a short-circuit current density (J(SC)) of 25.29 mA cm(-2), open-circuit voltage (V-OC) of 0.84 V, and fill factor (FF) of 76.13%. The hole/electron mobilities of the PM6:Y6-BO, 10% BT-rho, and 10% BT-rhoCN ternary devices were 2.20 x 10(-4)/1.85 x 10(-4) cm(2) V-1 s(-1), 3.66 x 10(-4)/3.77 x 10(-4) cm(2) V-1 s(-1), and 1.34 x 10(-4)/0.94 x 10(-4) cm(2) V-1 s(-1), respectively. The crystal coherence lengths (L(C)s) of the (010) peaks for the PM6:Y6-BO, 10% BT-rho, and 10% BT-rhoCN ternary films are 43.2, 60.8, and 33.7 A, respectively. The superior PCE of the 10% BT-rho ternary devices compared with that of the PM6:Y6-BO binary device is attributed to the enhanced hole and electron mobilities and the high crystallinity of the blend films, which contribute to the enhancement of the J(SC) and PCE.