Random D1–A1–D1–A2 terpolymers based on diketopyrrolopyrrole and benzothiadiazolequinoxaline (BTQx) derivatives for high-performance polymer solar cells†
We synthesized and characterized a series of new random terpolymers composed of two electron-accepting blocks, diketopyrrolopyrrole (DPP) and benzothiadiazolequinoxaline (BTQx), and one electron-donating benzo[1,2-b:4,5-b′]dithiophene (BDT) unit with different molar ratios of the BTQx block to DPP block (25%, 50%, and 75% BTQx). The random terpolymers compositional effects on the physicochemical properties and photovoltaic performances were studied. Different compositions of DPP and BTQx blocks in the conjugated backbone of the terpolymers had a crucial effect on the electrochemical and optical properties of the random terpolymers. These terpolymers were employed as a donor along with PC71BM as an acceptor for solution-processed polymer solar cells. Among all the terpolymers, P13 (BDT–DPP50–BTQx50) with a monomer composition of BTQx and DPP (50 : 50) blocks showed excellent light-collecting ability, high charge-carrier mobility, and a low-lying HOMO energy level. PSCs based on P13 (BDT–DPP50–BTQx50) exhibited a Voc of 0.86 V, a Jsc of 15.74 mA cm−2, and an FF of 0.68, leading to a high PCE of 9.20%, which is higher than that for D–A copolymers, i.e., P11 (7.37%) and P15 (8.11%). These results demonstrate that random terpolymerization is a simple and practical approach for optimization of a conjugated polymer donor for efficient polymer solar cells.