Novel perylene diimide based polymeric electron-acceptors containing ethynyl as the π-bridge for all-polymer solar cells

We designed and synthesised two n-type donor-acceptor copolymers based on perylenediimide (PDI). These copolymers contained an ethynyl moiety as the pi-bridge between PDI and the electron-donating unit of either benzodithiophene (BDT) or fluorine (F), with the corresponding polymers denoted as PPDI-BDT and PPDI-F, respectively. The molecular geometry and the optical and electrochemical properties of the polymers were affected by the electron-donating unit. Both copolymers exhibited relatively broad light-absorption profiles and deep lowest unoccupied molecular orbital energy levels of about -3.8 eV. All-polymer solar cells (all-PSCs) were fabricated using these copolymers as the electron-accepting material and a medium-bandgap conjugated polymer, PBDB-T, as the electron-donating material. The resulting all-PSC based on PPDI-F exhibited a power conversion efficiency of 5.09%, which is significantly higher than that of the device fabricated using PPDI-BDT (2.73%). This improvement was attributed to the higher open-circuit voltage, greater charge carrier mobility and more effective charge transfer of the PBDB-T:PPDI-F blend film. These results suggest that the developed n-type PDI-based copolymers are promising candidates as electron-accepting materials for the construction of high-performance all polymer solar cells. (C) 2017 Elsevier B.V. All rights reserved.