Strategy to Modulate the Electron-Rich Units in Donor–Acceptor Copolymers for Improvements of Organic Photovoltaics

We present an effective strategy to modulate the electron-rich capability in donor–acceptor (D-A) polymers for improving the performances of organic solar cell (OSC) devices. In order to confirm this strategy, based on a series of the reported D–A polymers ((PCPDTBT­(Pa1), PCPDTFBT (Pa2), and PCPDTDFBT (Pa3)) which contain the electron-donating cyclopentadithiophene (CPDT) and differently electron-withdrawing units of benzo­[c]­[1,2,5,]­thiadiazole (BT), 5-fluorobenzo­[c]­[1,2,5]­thiadiazole (FBT), and 5,6-difluorobenzo­[c] [1,2,5]­thiadiazole (DFBT), we replace CPDT with electron-donating dithienogermolodithiophene (DTTG) in polymers Pa1–Pa3, respectively, and design a series of new D–A polymers Pb1–Pb3. Compared with the polymers Pa1–Pa3, the new designed polymers Pb1–Pb3 not only yield a greater red-shift of the absorption spectrum of the donor polymer and result in a larger absorption region within the solar emission spectrum and an improved light-absorbing efficiency but also exhibit much better electron transfer efficiency in active layer, larger hole transport rates and higher open circuit voltage. Moreover, the estimated power conversion efficiency of the designed polymers in OSC applications reaches up to ∼8.4%. Conclusively, the approach based on modulating the electron-donating capability in D–A polymer chain is a feasible way to enhance their intrinsic properties of donor polymers and thereby achieving the purpose that improves the performances of the OSC devices