Conjugated polymers consisting of quinacridone and quinoxaline as donor materials for organic photovoltaics: orientation and charge transfer properties of polymers formed by phenyl structures with a quinoxaline derivative

Abstract

In this study, a highly soluble poly[quinacridone-alt-quinoxaline] series (PQCQx, PQCTQx, PQCTPz) was synthesized through the Suzuki coupling reaction by introducing planar quinacridone and highly soluble quinoxaline. The polymers were soluble in general organic solvents, and the M_n was 15.6–85.0 kg mol⁻¹. The optical band gap energy was 1.82–1.97 eV, which was similar to the band gap of a benzothiadiazole derivative. The HOMO and LUMO levels of the polymers were −5.32 to −5.46 eV and −3.40 to 3.50 eV, respectively. According to XRD measurements, the PQCQx and PQCTPz showed the formation of an ordered lamellar structure and conventional edge-on π-stacking, while the PQCTQx showed face-on formation relative to the substrate. This study also evaluated the OPV characteristics by fabricating a bulk-heterojunction-type polymer solar cell. For the device structure of ITO/PEDOT:PSS/active layer (PQCTQx:PC₇₁BM = 1 : 2 with DIO)/PFN/Al, the values of open-circuit voltage (V_OC), short-circuit current (J_SC), fill factor (FF) and power conversion efficiency (PCE) were 0.85 V, 7.6 mA cm⁻², 54.9%, and 3.6%, respectively.