Improved Performance of Inverted Near-Infrared Organic Photodetectors Based on ZnO/PFN as Double-Layer Interfacial Materials

In this article, the poly [(9,9 bis (3 ’-(N, N-dimethylamino-propyl)-2,7-(2, 9-dioctylfluorene)] (PFN) and zinc oxide (ZnO) are used as the double-layer electron transport layer (ETL). The performance of organic photodetector (OPD) can be effectively improved by adjusting the solvent, thickness, and annealing temperature of the active layer. According to the hydrophobicity analysis, the active layer can form closer contact with the ZnO/PFN double-layer ETL than pure ZnO device, thus forming the better interpenetrating network structure. According to the surface morphology analysis, the active layer deposited on ZnO/PFN has the more uniform phase separation. Compared with different ETL material, the number of trap states in the ZnO/PFN-based device is significantly reduced. The larger depletion layer width is obtained from the ZnO/PFN double-layer ETL device. The parallel resistance of double-layer ETL devices is much higher than that of single-layer ETL devices. The high carrier mobility of the device in the light condition indicates the fast response speed. The dark current density of ZnO/PFN double-layer ETL devices are reduced to 10−11 A cm−2, and the specific detectivity of up to 1013 Jones was obtained. These results indicate that near-infrared (NIR) OPDs based on ZnO/PFN double-layer ETL have great potential in health detection.