Effect of initial galvanic nucleation on morphological and optical properties of ZnO nanorod arrays

Zinc oxide (ZnO) nanorod arrays with controllable packing density have been prepared on transparent conductive oxide substrates using a short, simple galvanic nucleation step. The packing density of the ZnO nanorods (NR) was increased by ~ 200% from 8.5 × 108 cm− 2 to 1.7 × 109 cm− 2 by increasing the initial galvanic nucleation (IGN) current density from − 0.2 mA/cm2 to − 1.4 mA/cm2. Coinciding with the increase in NR density, a decrease in average NR diameter and length is observed. A strong influence of the IGN step on the optical properties can be correlated, despite otherwise identical deposition conditions. Photoluminescence measurements show decreasing Vis:UV emission, indicating a relative decrease of deep-level defects, and thus an improvement in crystal quality of the ZnO NR induced by the IGN step. The light scattering strongly decreases with increasing IGN current density, while simultaneously an increase in total and specular transmittance and a decrease in absorbance and reflectance are observed. Angular-resolved transmission and reflection measurements demonstrate non-Lambertian scattering with the angular distribution depending on wavelength and NR morphology. Thus, the variation of the IGN allows tuning the optical properties to optimize solar cell performance.