ZnO Transparent Conducting Thin Films Deposited by Ultrasonic Spray Pyrolysis, for Solar Energy Conversion

Abstract

Undoped and indium-doped zinc oxide thin films were deposited by ultrasonic spray pyrolysis (Pyrosol process) onto soda-lime glass substrates. Several precursors and solvents were tested for undoped zinc oxide thin film deposition. Only a solution of zinc acetate on methyl alcohol allowed us to obtain good quality ZnO thin films; indium doping was achieved by adding a few drops of a saturated solution of In(C5H702)3 on acetylacetone. Resistivities as low as 2·10-3 Ω-cm, Hall mobilities as high as 21 cm2/V-s and effective carrier concentrations as high as 1.3·1020 cm-3 have been obtained. Electron concentrations are always lower than indium contents on films. Average optical transmission on the whole visible range as high as 85% for the best conductive films has been obtained. Refractive index of layers is modified by the growth temperature and indium doping. Haacke’s figure of merit up to 5·10-3 Ω-1 in a 500 nm. thick films was obtained. Indium doping improves stability of the electrical properties of ZnO conducting films. This films are suitable for solar energy conversion, particularly in photovoltaic applications (ZnO/CdTe and ZnO/Si solar cells).