Fluorinated Thieno[2′,3′:4,5]benzo[1,2-d][1,2,3]triazole: New Acceptor Unit To Construct Polymer Donors

A new acceptor unit, fluorinated thieno[2',3':4,5]benzo[1,2- d ][1,2,3]triazole (fBTAZT), has been designed and synthesized to build two donor-acceptor (D-A) copolymers with the none/fluorinated benzodithiophene (BDT) unit, which have been applied as the electron-donating material with ITIC as an electron-accepting material to fabricate the nonfullerene polymer solar cells (PSCs). It is found that fluorination at the BTAZT unit and BDT unit exerts a significant influence on photophysical properties and photovoltaic performances of the PSCs. As a result, when the fluorine atom is introduced both into the BTAZT unit and the side-chain thiophene ring of the BDT unit, the corresponding polymer PfBTAZT-fBDT exhibits deeper highest occupied molecular orbital-lowest unoccupied molecular orbital energy level and shows stronger interchain interaction with a little broad and red-shift absorption and high charge mobilities as well as good phase-separated morphologies, thus leading to higher power conversion efficiency of 6.59% in nonfullerene PSCs compared with another polymer PfBTAZT-BDT without F atom at the BDT unit, indicating that fBTAZT can be acted as a medium strong organic acceptor to build D-A polymer donor for high efficient PSCs.