Solar light-driven hydrogen by photocatalytic water splitting over a semiconductor photoelectrode has been considered a promising green energy carrier. P-type semiconducting copper oxides (Cu2O and CuO) have attracted remarkable attention as an efficient photocathode for photoelectrochemical (PEC) water splitting because of their high solar absorptivity and optical band gaps. In this study, CuO thin films were prepared using the sol-gel spin coating method to investigate the effects of aging time and layer dependency. Electrodeposition was also applied to fabricate Cu2O thin films. Cu2O thin films annealed at 300 °C are a hetero-phase system composed of Cu2O and CuO, while those at 400 °C are fully oxidized to CuO. Thin films are characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-VIS), Fourier transform infrared spectroscopy (FTIR), spectroscopic ellipsometry (SE), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman microscopy. The hetero-phase thin films increase the photoconversion efficiency compared to Cu2O. Fully oxidized thin films annealed at 400 °C exhibit a higher efficiency than the hetero-phase thin film. We also verified that CuO thin films fabricated using electrodeposition show slightly higher efficiency than the spin coating method. The highest photocurrent of 1.1 mA/cm2 at 0.10 V versus RHE was measured for the fully oxidized CuO thin film under one-sun AM1.5G illumination. This study demonstrates a practical method to fabricate durable thin films with efficient optical and photocatalytic properties.

In this work, a high-mobility amorphous In-W-O thin transistor (a-IWO TFT) is studied for flat panel displays applications. The effects of oxygen content on the electrical performance and reliability of a-IWO TFTs are mainly investigated by modulating oxygen partial pressure during IWO channel deposition. Experimental results show the high oxygen partial pressure will degrade the electrical stability and cause a large threshold voltage shift (∆ ) in the a-IWO TFT device. To elucidate the origin of electrical instabilities, the interface trap densities, , at the interface between gate insulator and IWO layer as well as bulk trap density, , in the bulk of IWO film were extracted for comparisons. It shows that the interface states are increased as increasing oxygen partial pressures. The enhanced trapping of electron due to the increased interface states is considered to lead to large ∆ in the TFT with increasing oxygen partial pressures.