Fabrication of Transparent Conductive Zinc Oxide Co-Doped with Fluorine and Zirconium Thin Solid Films by Ultrasonic Chemical Pyrolysis: Effects of Precursor Solution Aging and Substrate Temperature

Highly transparent, conducting zinc oxide [ZnO] thin films co-doped with fluorine and zirconium have been deposited on glass substrates by the ultrasonic chemical spraying technique. The effects of aging of the starting solution and substrate temperature on the structural, morphological, and electrical properties of the ZnO:F:Zr films have been studied. The resistivity of the films decreases with the aging time of the starting solution until the seventeenth day reaching a minimum of about ？？？cm and then increases. Though all the samples are of polycrystalline hexagonal wurtzite type and grow preferentially with (002) plane parallel to the substrate, their morphology depends strongly on the aging time of the reaction solution. The optical transmittance of all the films remained around 80% in the visible spectral range. These highly transparent, low resistive thin films are expected to be highly useful as transparent electrodes in the fabrication of thin film solar cells. 1. Introduction The demand of low-cost and high-performance optoelectronic devices leads to the development of more efficient transparent conductive oxide (TCO) thin films. Among the popular TCOs, the last decade has seen the emergence of zinc oxide [ZnO] as one of the most important materials for manufacturing transparent electrodes utilized in the fabrication of amorphous silicon-based solar cells. Apart from their high optical transparency, the ZnO thin films are highly stable in the hydrogen-plasma environment commonly used for the fabrication of silicon-based p-i-n structures [1]. ZnO thin films have been deposited by a wide variety of techniques, like evaporation [2], sputtering [3], chemical vapor deposition [4, 5], sol-gel [6, 7], and chemical spray [8, 9], among others. Among those, the chemical spray technique has been successfully used for the deposition of conductive and transparent ZnO thin films. Keeping in mind the high optical transparency as one of the basic requirements, incorporation of several dopants has been tried to reduce the resistivity of ZnO films. On the other hand, like all the chemical deposition techniques, chemical spray technique involves several parameters or deposition conditions which control the physical properties of the fabricated thin films. However, a complete knowledge of the effect of deposition conditions on the physical characteristics of ZnO thin films is far from being reached. The spray pyrolysis technique is based on the pyrolytic decomposition of small droplets of a zinc-containing solution onto a heated substrate, under atmospheric