Narrowband Ultraviolet Photodetectors Based on Nanocomposite Thin Films with High Gain and Low Driving Voltage

Abstract

Narrowband ultraviolet (UV) photodetectors are highly desired in multiple areas. Photodetectors based on organic–inorganic nanocomposites offer high sensitivity, widely adjustable response range, light weight, and low-temperature solution processibility. However, the broad absorption range of organic and inorganic semiconductor materials makes it difficult to achieve a narrowband detection feature for nanocomposite photodetectors. In this work, nanocomposite thin films containing the wide band gap conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(bithiophene)] (F8T2) blended with wide band gap ZnO nanoparticles (NPs) serve as the active layers of the photodetectors. Narrowband UV photodetectors with high gain and low driving voltage are demonstrated by adopting a symmetric device structure, controlling the active layer composition and microstructure, and manipulating the light penetration depth in the active layer. The fabricated photodetector exhibits a high external quantum efficiency of 782% at 358 nm under a low forward bias of 3 V with the full-width at half-maximum of 16 nm. Combined with a low dark current, a high specific detectivity of 8.45 × 1012 Jones is achieved. The impacts of the F8T2:ZnO NPs weight ratio and the device structure on the UV-selectivity and the device performance are investigated and discussed. Our method offers a pathway to design and fabricate narrowband UV photodetectors.