Graphene quantum dot (GQD)-sensitized ZnO nanorods/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) Schottky junction has been fabricated for visible-blind ultraviolet (UV) photodetector applications. Schottky diode parameters such as ideality factor, effective work function, and series resistance have been studied for GQD-modified and pristine ZnO nanorod-based devices. Under illumination of broadband light of intensity 80 mW/cm, GQD-sensitized samples showed 11 times higher photocurrent value compared to pristine ZnO at -0.75 V external bias. GQD-modified detector demonstrated maximum photocurrent at UV region (wavelength ∼340 nm) for all reverse bias voltages. ZnO nanorods/polymer Schottky junction UV detectors revealed high external quantum efficiency (EQE) more than 100%. Interestingly, GQD sensitized nanorod-based device demonstrated high EQE value of 13,161% at -1 V bias (wavelength ∼340 nm), which is eight times higher than pristine ZnO NR-based detector. GQD-modified detectors also showed superior responsivity (36 A/W), detectivity (1.3 × 10 Hz/W) at -1 V bias under incident of light of wavelength 340 nm. Even at very low intensity of UV light (0.07 mW/cm), GQD-modified UV detectors showed high photocurrent (∼7.0 mA/cm).

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Vertically aligned TiO2 nanorods (NRs) were synthesized on a fluorine-doped tin oxide-deposited glass substrate by the hydrothermal method. A Schottky junction ultraviolet photodetector was fabricated by spin-coating of the poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) polymer on TiO2 NRs. For the improvement of device performance, the electrical conductivity of the polymer was increased by adding dimethyl sulfoxide (DMSO) and concentrated H2SO4 acid. The diode parameters, i.e., work function, series resistance, and ideality factor, were studied for all devices. Photoresponse behavior of the TiO2 nanorod/PEDOT:PSS junction was studied upon illumination of white light of intensity 80 mW/cm2. Our acid-treated sample demonstrated the highest photocurrent value, which is 10 times larger than that of DMSO-treated and 39 times larger than that of the untreated sample. Our acid-treated device showed superior external quantum efficiency (∼12 560%), responsivity (∼34.43 A/W), and detectivity (∼1.6 × 1011 Hz1/2/W) at ∼340 nm wavelength under −1 V bias.

Nitrogen‐doped graphene quantum dots (N‐GQDs) have been synthesized using a hydrothermal process. The N‐GQDs are highly crystalline with a size of 3–7 nm and made up of 1–3 layers of graphene. UV/Vis absorption studies reveal two major absorption peaks at 237 and 334 nm, which are attributed to the π→π* transition of C=C and n→π* transition of C=O bonds, respectively. The additional broad peak observed at 460–500 nm is attributed to the n→π* transition of C=N bonds. The N‐GQDs are highly luminescent and exhibit excitation‐dependent emission. The photoelectrochemical properties of pristine ZnO and N‐GQD‐sensitized ZnO nanorods have been investigated. N‐GQD‐sensitized nanorod photoanodes demonstrate superior photoconversion efficiency, incident photon‐to‐current conversion efficiency, and power conversion efficiency compared with pristine ZnO nanorods.