Novel self-doping alcohol-soluble quinacridone-based small molecule at the cathode interface layer of organic solar cells

Interfacial modification plays a crucial part in improving the photovoltaic performance and stability of organic solar cells (OSCs). The self-doping effect can enhance the inter-ohmic contact at the active layer material with the cathode. Therefore, we synthesised a self-doping alcohol-soluble quinacridone-based small molecule, 5,12-bis(3-(dimethylamino)propyl)-5,12-dihydroquinolo[2,3-b]acridine-7,14-dione (QAN), with a self-doping effect, and introduced QAN as cathode interfacial layers (CILs) into OSCs. The central nuclear structure of QAN is an electron-deficient unit with a large conjugated structure. This structure facilitates electron transport as a cathode-interface material. Additionally, its polar side chains enhance the solution-processing capability and contribute to a more pronounced self-doping effect. Compared with the devices without interfacial material, the open-circuit voltage(V-OC) and short-circuit current (J(SC)) with QAN as an interfacial material increased. What's more, the optimal photoelectric conversion efficiency (PCE) of the QAN CIL device is increased to 9.05 % for the same experimental conditions, which is 40 % higher than the device without interface material. By characterizing the surface morphology, it was found that the PTB7-Th:PC71BM active layer devices exhibited a smooth surface morphology and improved hydrophilicity when inserted with QAN CIL, which helps to enhance the physical contact of the active layer with the cathode, in addition to charge extraction and transport. This result suggests that introducing QAN as the CILs of the device is a viable way to improve the performance of the OSCs.