High-efficiency non-fullerene polymer solar cell fabricated by a simple process using new conjugated terpolymers

Abstract

A series of conjugated terpolymers, P2–P4, based on 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene as the electron-donating unit, methyl-3-thiophenecarboxylate (3MT) as the weak electron-accepting unit, and 1,3-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) as the strong electron-accepting unit were synthesized to investigate the effect of the contents of 3MT and BDD on their optical and electrochemical properties and the performance of the derived fullerene-free polymer solar cell (PSC) devices. By varying the contents of 3MT and BDD in the terpolymer structure, the solubility, absorption range, and energy levels could be efficiently tuned. Among the three terpolymers, the as-cast blend film of P3:acceptor with complementary absorption and favorable internal morphology exhibited the highest power conversion efficiency of 10.26% with a high open circuit voltage of 0.94 V and short circuit current density of 17.18 mA cm⁻² in the PSC. Although the three repeating units were randomly arranged along the polymer backbone, their PSCs exhibited an excellent shelf-life of over 1000 h under ambient conditions, which is as good as those of binary D–A copolymers.