Random D-A1-D-A2 terpolymers based on benzodithiophene, thiadiazole[3,4-e]isoindole-5,7-dione and thieno[3,4-c]pyrrole-4,6-dione for efficient polymer solar cells

Recent developments on regio-regular and randomterpolymers based on a donor/acceptor architecture (D-1-A-D-2-A or D-A(1)-D-A(2)) have shown promising results for their use as donormaterials in bulk heterojunction (BHJ) polymer solar cells. New random terpolymers including benzo[1,2-b: 4,5-b']-dithiophene (BDT) as the electron-donor moiety and thiadiazolo[3,4-e] isoindole-5,7-dione (TID) and thieno[3,4-c]pyrrole-4,6-dione (TPD) as electron-accepting moieties were synthesized by Stille cross-coupling polymerization. Incremental addition of TPD (from 0 to 90%) led to the following random terpolymers: P[(BDT-TID)(x)-(BDT-TPD)(y)](n). Their electro-optical and photovoltaic properties were investigated. These high molecular weight and highly processable random terpolymers exhibited broad and strong absorption (300-800 nm), moderate bandgaps (1.52 eV to 1.64 eV) and deep-lying HOMO/LUMO energy levels (-5.6 eV and -3.9 eV, respectively). First, the optimized inverted device ITO/ZnO/P1: PC71BM/MoO3/Ag (where P1 is a typical D/A copolymer; TID 100%; TPD 0%) showed a power conversion efficiency up to 6.36% which is higher than the PCE reported in the literature for an analog of P1 (3.42%). Then, devices based on random terpolymers (P2-P10) showed power conversion efficiencies ranging from 5.06% (for P7; 40% TID/60% TPD) up to 6.70% (for P2; 90% TID/10% TPD) when PC61PM is used as the electron acceptor. A PCE as high as 7.30%, a Voc of 0.81 V, a Jsc of 13.86 mA cm(-2) and a FF of 65% were achieved for P2 when PC71PM was used. This PCE is among the highest PCE values reported for random terpolymer-based polymer solar cells.