Hierarchical Zinc Oxide Nanostructures: Enhancement in Optical Properties for Photoelectrochemical Photodetector

Abstract

This study reports the preparation of zinc oxide nanorod arrays (ZnO NRAs) on patterned glass substrates via the photolithography method to be used as photoanode material for photoelectrochemical photodetector (PEC PD) applications. The excellent alignment of ZnO NRAs has been observed on the patterned substrates via photolithography. Therefore, the effects of circular patterns having different circle diameters (D:20 µm, 2D:40 µm, 4D:80 µm in diameter) and the distance between circles have been investigated in the PEC PD application. ZnO thin films have been prepared by physical vapor deposition using RF magnetron sputtering. Subsequently, the photoresist has been spun on the ZnO layer, followed by exposure to laser light with 375 nm of wavelength. Vertically aligned ZnO NRAs have been grown on the patterned surface by the facile chemical bath deposition method. Surface analysis of patterned substrates of ZnO NRAs has been performed via optical profilometry. First, the effects of the diameter changes of the circles and the distance between the circles in the pattern on PEC PD performance have been verified in various electrolytes. PEC PD measurements have been performed under applied potential (-1V to +0.4V voltage (vs. Ag/AgCl)) at UV irradiation and dark condition to obtain responsivity, selectivity, and detectivity parameters. Second, ZnO NRAs have been coated with an indium sulfide (In2 S3 ) thin film layer using the ultrasonic spray pyrolysis method to shift the light absorption through the visible region. It has been determined that In2 S3 -coated ZnO NRAs provided the highest charge transfer at the photoanode/electrolyte interface when the diameter of circles is D in pattern and the distance between the circles is decreased.