Solution-processed ZnO:graphene quantum dot/Poly-TPD heterojunction for high-performance UV photodetectors

Abstract

Recently, ZnO-based photodetectors have gained immense attention for ultraviolet detection applications owing to their abundance and cost-effective synthesis. However, low responsivity, slow speed, and complicated fabrication limit the applications of these detectors. Herein, we report a high-performance UV photodiode based on n-type graphene quantum dot-decorated ZnO (ZnO:GQD) and p-type poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine (Poly-TPD) heterojunction. First, we demonstrate the incorporation of GQD in ZnO not only reduces the ZnO surface roughness and ZnO nanoparticle size but also promotes the transport of photogenerated carriers and increases the charge lifetime of ZnO. The effect of GQD content on the physical and chemical characteristics of the ZnO film is investigated using Raman spectroscopy, XRD, SEM, AFM, UV-vis spectroscopy, and PL. Second, under the appropriate GQD concentration condition, the performances of various ZnO:GQDbased devices are compared to understand the charge transport mechanism. As a result, the photodiode based on ZnO:GQD/Poly-TPD shows the most balanced energy structure, enhanced mobility, and alleviation in charge recombination relative to the other devices. The ZnO:GQD/Poly-TPD photodetector exhibits excellent performance under 365-nm UV illumination: a rise/decay time of 0.37/0.78 s and a specific detectivity of 2.1 x 10(11) Jones (at -3 V bias) with outstanding stability at least for 10 weeks without significant photocurrent degeneration.