In this study, the structural, optical, and electrical effects of Hf incorporation as a function of Hf atomic concentration were investigated using the solution process. Increases of Hf incorporation in Hf-InZnO (HIZO) thin films were associated with segregation of each element, and enhancement of optical bandgap energy and absorbance. We suggested that Hf could replace Ga as a carrier suppressor in the InZnO (IZO) system due to its low standard electrode potential, a property that reflects the oxidizing tendency of a metal cation. We observed that even small doses of Hf also resulted in the effective reduction of the carrier concentration in the IZO system. An increase of Hf incorporation in HIZO TFTs caused electrical properties including on-current, threshold voltage, and subthreshold swing to decrease, shift positively, and increase, respectively. (C) 2010 Elsevier B.V. All rights reserved.