N-pentylisatin and ZnO NWs based organic-inorganic hybrid device for broad range photodetection

Abstract

In this work, a two-terminal and broad spectral range organic-inorganic hybrid photodetector device containing N-pentylisatin -based compound coated semiconducting Zinc oxide (ZnO) nanowires (NWs) on a glass substrate is fabricated. In SEM measurement, the average diameter of the hexagonal top tips, typical for ZnO NWs, was found to be ∼170 nm whereas, the XRD spectrum showed a single well-pronounced peak at 34.36° corresponding to 002 plane of ZnO with an average crystallite size of ∼90 nm, thus confirming the vertical-alignment as well as high crystallinity of ZnO NWs. Moreover, in the SEM images, the N-pentylisatin was observed to fill and cover the sidewalls and top tips of the ZnO NWs. The UV–Vis–NIR optical absorption spectra showed an absorption edge at 2.38eV for N-pentylisatin, 3.08 eV for as-synthesized (pristine) ZnO NWs thin film, and the absorption edge shifted to NIR for hybrid thin-film, i.e., N-pentylisatin coated ZnO NWs thin film. This extended range absorption in the hybrid film is attributed to the optical excitation from the HOMO level of N-pentylisatin to the conduction band (CB) of ZnO NWs. The coated devices showed the photoresponse for all LEDs (IR, red, green, blue), whereas the pristine NWs (without N-pentylisatin coating) showed only response to Blue and White LEDs. The photosensitivity (photo to dark current ratio) of the hybrid device is two to three orders of magnitude larger than the pristine device for the entire Visible (blue, green, red) to IR range. It would be worthwhile to mention that the conductivity of the ZnO NWs thin film was reduced almost 10 to 100 times after coating with N-pentylisatin, thereby indicating that terminating oxygen molecules of the N-pentylisatin act as an electron acceptor.