We fabricated inverted polymer solar cells (PSCs) using an organic–inorganic hybrid interlayer for electron extraction. The surface energy and surface defects of an organic–inorganic ZnO–PFN hybrid film, which was prepared by dissolving the conjugated polymer electrolyte poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)] (PFN) in a ZnO solution, were reduced, compared to ZnO film. By introducing the ZnO–PFN electron extraction layer, the interfacial contact between the active and electron extraction layers was improved and the series resistance of the PSC device was decreased. As a result, electron extraction from the active layer to the electrode was enhanced. The highest power conversion efficiency (PCE) of the inverted PSCs was 9.2%. Moreover, the ZnO–PFN-based inverted PSCs showed improved long-term stability compared to ZnO-based devices. The ZnO–PFN interlayer aimed to overcome the drawbacks of the conventional hydrophilic surface of ZnO, based on the properties of the conjugated polymer (PFN) without the need for additional processes. It was therefore simple to fabricate the inverted PSCs, making the devices commercially viable.

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.