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

Abstract

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. Three donor polymers based on IDT unit and Phenanthrenequinoxaline derivatives were developed. The photovoltaic performance was improved by tuning the number of fluorine on the phenanthrenequinoxaline moiety. High efficiency was obtained without the use of additives, thus simplifying processing of efficient polymer solar cells. • Three polymers based on indacenodithiophene and phenanthrenequinoxaline units were designed for photovoltaic applications. • The mono-fluorinated polymer PIDT-FphanQ delivers a best PCE of 11.6% due to higher J sc and FF. • The high photovoltaic performance was achieved without solvent additives, simplifying the process for efficient PSC.