Investigation of hydrothermal growth time and temperature for optimized ZnO nanowire arrays toward photovoltaics

Abstract

The challenge of meeting energy demands has led to the development of nanotechnology. Semiconductor nanowires are considered a promising option among various nanomaterials for efficiently capturing solar radiation in an axial geometry. This work presents the growth of ZnO nanowire arrays on seeded-coated glass substrates using a two-step hydrothermal method, by examining the effect of two crucial hydrothermal growth parameters: time and temperature of growth. X-ray diffraction (XRD) spectra showed the hexagonal wurtzite shape of the ZnO nanowires which displayed a preferred (002) axial orientation. To estimate the crystallite size, strain, stress, and energy density values, we used the Modified Williamson-Hall models. Scanning electron microscopy (SEM) observations showed that the growth time and temperature have a significant impact on the length and diameter of the nanowires, which increase with increasing time and temperature. A clear correlation was also observed between the diameter and density of the nanowires. Optical analysis showed that ZnO nanowires exhibited good transmittance of about 90% in the near ultraviolet and visible spectrum, but this decreased with increasing growth time and temperature. The measured bandgap energy showed a red shift, which confirmed its correlation with the structural characteristics. The improved optical and structural features of ZnO nanowires were analyzed with regards to their potential use in photovoltaics.