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 Voc 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 Jsc and FF. The best PCE was recorded to be 11.6% with a Voc of 0.79 V, a Jsc 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.