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

Abstract

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 π-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 ∼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 × 10 −4 /1.85 × 10 −4 cm 2 V −1 s −1 , 3.66 × 10 −4 /3.77 × 10 −4 cm 2 V −1 s −1 , and 1.34 × 10 −4 /0.94 × 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 Å, 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. • New BT-based acceptors, BT-rho and BT-rhoCN, were synthesized by inserting rhodanine terminal groups. • Rhodanine end groups of BT-rho lowered the LUMO level and thus increased the open-circuit voltage. • An enhanced PCE of 16.17% was achieved using BT-rho as a third component in a PM6:Y6-BO blend.