Interrelation between Chemical, Electronic, and Charge Transport Properties of Solution-Processed Indium-Zinc Oxide Semiconductor Thin Films

Solution-processed metal oxide semiconductors are of high interest for the preparation of high-mobility transparent metal oxide (TMO) semiconductor thin films and thin film transistors (TFTs). It has been shown that the charge transport properties of indium-zinc oxide (IZO) thin films from molecular precursor solutions depend strongly on the preparation conditions, in particular on the precursor conversion temperature T-pc and, to some surprise, also on the concentration of the precursor solution. Therefore, the chemical and the electronic structure of solution-processed IZO thin films have been studied in detail with Xray photoelectron spectroscopy (XPS) under systematic variation of Tpc and the concentration of the precursor solution. A distinct spectral feature is observed in the valence band spectra close to the Fermi level at E-B = 0.45 eV binding energy which correlates with the trends in the sheet resistivity, the field effect mobility mu(FE), and the optical gap E-g(opt) from four-point-probe (4PP), TFT, and UV-vis measurements, respectively. A comprehensive model of the interrelation between the conditions during solution-processing, the chemical and electronic structure, and the charge transport properties is developed.