A highly efficient random copolymer showing a record PCE of 7.03% was prepared.

Pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (DPPD)‐based large band gap polymers, P(BDT‐TDPPDT) and P(BDTT‐TDPPDT), are prepared by copolymerizing electron‐rich 4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) unit with novel electron deficient 2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (TDPPDT) unit. The absorption bands of polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) cover the region from 300 to 600 nm with an optical band gap of 2.11 eV and 2.04 eV, respectively. The electrochemical study illustrates that the highest occupied/lowest unoccupied molecular orbital energy levels of P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) are −5.39 eV/−3.28 eV and −5.44 eV/−3.40 eV, respectively. The single layer polymer solar cell (PSC) fabricated with a device structure of ITO/PEDOT:PSS/P(BDT‐TDPPDT) or P(BDTT‐TDPPDT):PC70BM+DIO/Al offers a maximum power conversion efficiency (PCE) of 6.74% and 6.57%, respectively. The high photovoltaic parameters such as fill factor (∼72%), open circuit voltage (Voc, ∼0.90 V), incident photon to collected electron efficiency (∼76%), and PCE obtained for the PSCs made from polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) make them as promising large band gap polymeric candidates for PSC application. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3564–3574

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Two benzodithiophene (BDT)‐based broad absorbing low band gap random copolymers, P1 and P2, incorporating electron accepting imide functionalized pyrrolo[3,4‐c]pyrrole‐1,3‐dione (TDPPDT) and lactam functionalized pyrrolo[3,4‐c]pyrrole‐1,4‐dione (DKPP) derivatives are prepared. The copolymerization of differently alkylated two TDPPDT derivatives with both of BDT and DKPP offers random copolymers P1 and P2. The absorption bands of polymers P1 and P2 cover the region from 300 to 900 nm and the estimated band gaps of P1 and P2 are 1.43 and 1.39 eV, respectively. The highest occupied molecular orbital energy levels of P1 and P2 are identical, at –5.25 eV. The organic field effect transistors made from P1 and P2 provide a hole mobility μ of 3.0 × 10−4 and 3.6 × 10−5 cm2 V−1 s−1, respectively. Polymer solar cells (PSCs) prepared from P1 and P2 afford a maximum power conversion efficiency of 1.64% and 2.14%, respectively.