High-performance organic solar cells based on a small molecule with thieno [3,2-b]thiophene as π-bridge

Herein, we synthesized a new acceptor-p-donor-p-acceptor (A-pi-D-pi-A) type small molecule donor material BTTR based on thienyl-substituted benzo[1,2-b:4,5-b'] dithiophene (BDT-T) as the electron-donating core, thieno [3,2-b] thiophene (TT) along with two thiophene units as the pi-bridge, and 3-ethylrhodanine (TR) as the electron-deficient end group. The optical, electrical, thermal properties and photovoltaic performance were investigated. BTTR shows strong absorption in the range of 300-700 nm, deep-lying HOMO energy level of -5.32 eV and high hole mobility of 1.01 x 10(-3) cm(2) V-1 s(-1). The organic solar cells (OSCs) based on BTTR: PC71BM (1:0.8, w/w) blend with tetrahydrofuran (THF) solvent vapor annealing (SVA) exhibited an optimized power conversion efficiency (PCE) of 8.0% with an open circuit voltage (V-oc) of 0.93 V, a short circuit current density (J(sc)) of 13.2 mA cm(-2), and a fill factor (FF) of 65.4% under the illumination of AM 1.5G, 100 mW cm(-2). The good photovoltaic performance indicates BTTR could be a promising donor material in solution-processed OSCs.