ZnO/Cu/ZnO (ZCZ) thin films were deposited at room temperature on a glass substrate using direct current (DC) and radio frequency (RF, 13.56 MHz) magnetron sputtering and then the effect of post-deposition electron irradiation on the structural, optical, electrical and transparent heater properties of the films were considered. ZCZ films that were electron beam irradiated at 500 eV showed an increase in the grain sizes of their ZnO(102) and (201) planes to 15.17 nm and 11.51 nm, respectively, from grain sizes of 13.50 nm and 10.60 nm observed in the as deposited films. In addition, the film’s optical and electrical properties also depended on the electron irradiation energies. The highest opto-electrical performance was observed in films electron irradiated at 500 eV. In a heat radiation test, when a bias voltage of 18 V was applied to the film that had been electron irradiated at 500 eV, its steady state temperature was about 90.5 °C. In a repetition test, it reached the steady state temperature within 60 s at all bias voltages.

ZnO thin films are of considerable interest because they can be customized by various coating technologies to have high electrical conductivity and high visible light transmittance. Therefore, ZnO thin films can be applied to various optoelectronic device applications such as transparent conducting thin films, solar cells and displays. In this study, ZnO rod and thin films are fabricated using aqueous chemical bath deposition (CBD), which is a low-cost method at low temperatures, and environmentally friendly. To investigate the structural, electrical and optical properties of ZnO for the presence of citrate ion, which can significantly affect crystal form of ZnO, various amounts of the citrate ion are added to the aqueous CBD ZnO reaction bath. As a result, ZnO crystals show a nanorod form without citrate, but a continuous thin film when citrate is above a certain concentration. In addition, as the citrate concentration increases, the electrical conductivity of the ZnO thin films increases, and is almost unchanged above a certain citrate concentration. Cu(In,Ga)Se2 (CIGS) solar cell substrates are used to evaluate whether aqueous CBD ZnO thin films can be applicable to real devices. The performance of aqueous CBD ZnO thin films shows performance similar to that of a sputter-deposited ZnO:Al thin film as top transparent electrodes of CIGS solar cells.

ZnO crystals with different morphologies are synthesized through thermal evaporation of the mixture of Zn and Cu powder in air at atmospheric pressure. ZnO crystals with wire shape are synthesized when the process is performed at 1,000 oC, while tetrapod-shaped ZnO crystals begin to form at 1,100 oC. The wire-shaped ZnO crystals form even at 1,000 oC, indicating that Cu acts as a reducing agent. As the temperature increases to 1,200 oC, a large quantity of tetrapod-shaped ZnO crystals form and their size also increases. In addition to the tetrapods, rod-shaped ZnO crystals are observed. The atomic ratio of Zn and O in the ZnO crystals is approximately 1:1 with an increasing process temperature from 1,000 oC to 1,200 oC. For the ZnO crystals synthesized at 1,000 oC, no luminescence spectrum is observed. A weak visible luminescence is detected for the ZnO crystals prepared at 1,100 oC. Ultraviolet and visible luminescence peaks with strong intensities are observed in the luminescence spectrum of the ZnO crystals formed at 1,200 oC.

We report on the fabrication and photoelectrochemical(PEC) properties of a Cu2O thin film/ZnO nanorod array oxide p-n heterojunction structure with ZnO nanorods embedded in Cu2O thin film as an efficient photoelectrode for solardriven water splitting. A vertically oriented n-type ZnO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type Cu2O thin film was directly electrodeposited onto the vertically oriented ZnO nanorods array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were characterized using X-ray diffraction and scanning electron microscopy as well as Raman scattering. The PEC properties of the fabricated Cu2O/ZnO p-n heterojunction photoelectrode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the Cu2O/ZnO photoelectrode was found to exhibit a negligible dark current and high photocurrent density, e.g., 0.77 mA/cm2 at 0.5 V vs Hg/HgCl2 in a 1 mM Na2SO4 electrolyte, revealing an effective operation of the oxide heterostructure. In particular, a significant PEC performance was observed even at an applied bias of 0 V vs Hg/ HgCl2, which made the device self-powered. The observed PEC performance was attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential, including the light absorption and separation processes of photoinduced charge carriers.