Fluorinated phenanthrenequinoxaline-based D-A type copolymers for non-fullerene polymer solar cells

Three polymers with indacenodithiophene (IDT) as the electron-rich unit and phenanthrenequinoxaline (phanQ) or fluorine substituted phenanthrenequinoxaline (FphanQ, 2FphanQ) as the electron-deficient units have been synthesized. The band gaps of PIDT-phanQ, PIDT-FphanQ, PIDT-2FphanQ were estimated to be 1.68, 1.68 and 1.71 eV with a HOMO energy level of -5.28, -5.33 and -5.41 eV, respectively. The photovoltaic performance of the three polymers in non-fullerene polymer solar cells with Y6 as the acceptor material was carefully investigated. The corresponding devices showed improved V-oc as the fluorine atom increased in the phanQ unit, but the champion PCE was achieved in the PIDT-FphanQ:Y6 based device due to its higher J(sc) and FF. The best PCE was recorded to be 11.6% with a V-oc of 0.79 V, a J(sc) of 21.4 mA cm(-2) and a FF of 68.7% for the PIDT-FphanQ:Y6 blend without using additives. The results indicate that the proper design in donor and acceptor units of D-A conjugated polymer, i.e. introducing the moderate fluorine substitutes, will be able to simplify the processing for the efficient PSCs applications.