Multi-donor random terpolymers based on benzodithiophene and dithienosilole segments with different monomer compositions for high-performance polymer solar cells

We synthesized and characterized a series of new random terpolymers which are composed of two electron-rich segments, thienyl-substituted benzo[1,2-b:4,5-b’]dithiophene (BDT) and dithieno[3,2-b:2’,3’-d]silole (DTS), and one electron-deficient segment, thieno[3,4-c]pyrrole-4,6-dione (TPD), with different ratio of DTS segment to BDT segment (25%, 50%, and 75% DTS). The compositional effect of the random terpolymers on physicochemical properties and photovoltaic performances were studied. The different compositions of BDT and DTS segments in the conjugated backbone of the terpolymers had a crucial effect on the electrochemical properties of the random terpolymers. PTPD-BDT75-DTS25 (P1) with monomeric composition of BDT and DTS (75:25) segments showed excellent light harvesting ability, high charge carrier mobility, and low-lying HOMO energy level. Moreover, the photovoltaic performance of the random terpolymer based BHJ PSCs was strongly influenced by the composition of BDT and DTS segments in the conjugated backbones of the terpolymers. The inverted BHJ PSCs based on the PTPD-BDT75-DTS25 exhibited a V_oc of 0.94 V, a J_sc of 10.83 mA/cm², and a FF of 56.52%, leading to a high PCE of 5.78%.