Electrodeposition of ZnO layers for photovoltaic applications: controlling film thickness and orientation

Abstract

A systematic study of the effect of the zinc oxide (ZnO) electrodeposition parameters (concentration, temperature, potential and pH) on film morphology, thickness, transparency, roughness and crystallographic orientation is presented with the view of producing optimized thin, planar, and continuous ZnO films for photovoltaic applications. Electrochemical measurements of the deposition charge as a function of time are used to understand the mechanism of nucleation and textured growth. Continuous thin films of crystalline ZnO are obtained at temperatures below 100 °C without the need for subsequent annealing. The formation of continuous films is favoured by high concentrations of Zn²⁺ precursor (> 100 mM), high temperature (> 70 °C) and low potentials (< −1.1 V/AgAgCl). A low bulk solution pH is shown to be a key factor in obtaining thin continuous films and the crystallographic orientation of these films can also be controlled by the deposition parameters. The importance of orientation and thickness control on device performance is shown by using the electrodeposited films as electron extracting interlayers in a model organic photovoltaic system.