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P-type CuO-Cu2O nanocomposite semiconductors composed of Cu2O-embedded CuO aggregations and Cu2O aggregation consisting of space-filling CuO grains have been fabricated by photoelectrochemical high-frequency potential-switching of 100 to 1000 cycles in an aqueous solution containing copper(II) sulfate hydrate, tartaric acid, and sodium hydroxide, and the size of both the CuO and Cu2O grains decreased from 40–44 nm to approximately 10 nm remaining the characteristic monoclinic and cubic lattices with an increase in cycle numbers. The bandgap energy of CuO components was almost a constant value of 1.5 eV, and the Cu2O components showed a decrease in bandgap energy from 2.05 eV to 1.85 eV with an increase in cycle number due to the Cu2+ state incorporation, and the CuO-Cu2O nanocomposites possessed an ionization energy of approximately 5.2 eV and work function of approximately 4.6 eV respectively, and were close to those for single CuO and Cu2O layers.

A metallic Cu layer with a sheet resistance of 0.19 Ω was chemically prepared on a glass substrate by chemical reduction of the intermediate Cu(OH)2/Cu(O,S) bilayers using dimethylamine-borane (DMAB), while Cu(OH)2, and Cu(O,S) layers were fabricated by a sequential chemical bath deposition (CBD) in aqueous solutions containing copper (II) nitrate hydrate and ammonium nitrate with urea and thiourea. The thickness of the Cu(OH)2 and resultant Cu layers were strongly affected by the structure under the Cu(O, S) layer, and a metallic Cu layer was formed mainly from the Cu(OH)2 layer. The reduction reactions of Cu(OH)2 and Cu(O, S) were discussed based on thermodynamics.

The quality of a semiconductor, which strongly affects its performance, can be estimated by its photoluminescence, which closely relates to the defect and impurity energy levels. In light of this, it is necessary to have a measurement method for photoluminescence properties with spatial resolution at the sub-micron or nanoscale. In this study, a mapping method for local photoluminescence properties was developed using a focused synchrotron radiation X-ray beam to evaluate localized photoluminescence in bi-layered semiconductors. CuO/Cu2O/ZnO semiconductors were prepared on F:SnO2/soda-lime glass substrates by means of electrodeposition. The synchrotron radiation experiment was conducted at the beamline 20XU in the Japanese synchrotron radiation facility, SPring-8. By mounting the high-sensitivity spectrum analyzer near the edge of the CuO/Cu2O/ZnO devices, luminescence maps of the semiconductor were obtained with unit sizes of 0.3 μm × 0.3 μm. The devices were scanned in 2D. Light emission 2D maps were created by classifying the obtained spectra based on emission energy already reported by M. Izaki, et al. Band-like structures corresponding to the stacking layers of CuO/Cu2O/ZnO were visualized. The intensities of emissions at different energies at each position can be associated with localized photovoltaic properties. This result suggests the validity of the method for investigation of localized photoluminescence related to the semiconductor quality.

The internally stacked CuO/Cu2O photoactive layers were prepared by electrodeposition of the Cu2O layer followed by heating in air. The 1.4 eV-p-CuO layer was heteroepitaxially grown on the Cu2O la...

Hematite (α-Fe2O3) films were prepared by cathodic polarization in an aqueous solution containing iron (Ⅱ) sulfate hydrate, potassium hydroxide, dimethylamine-borane (DMAB), and L-ascorbic acid and their structural and magnetic characteristics were investigated with X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscope observation, optical absorption measurement, and vibrating sample magnetometer (VSM), in addition to electrochemical characterizations for the electrodeposition before and after heating in ambient atmosphere and vacuum. The hematite films prepared at −1.0 and −1.1 V possessed characteristic hexagonal lattice and bandgap energy around 2.2 eV, and some amount of Fe2+ was contained in the hematite film, with increased Fe2+ content at −1.0 V. The films prepared at −0.8 and −0.9 V showed characteristic hematite bandgap energies with a decreased absorption but did not show any structural characteristics from the XRD and Raman spectra. The hematite films prepared at −1.0 V, and −1.1 V showed ferromagnetic features with 11 A·m2·kg−1 and 2.3 A·m2·kg−1 in saturation mass magnetization and 29.5, and 25 mT in coercivity, respectively. The hematite film was thermally transformed to magnetite (Fe3O4) possessing characteristic cubic lattice by heating at 673 K in vacuum, and the saturation mass magnetization increased to 89.2 A·m2·kg−1.

Scintillators, which convert high-energy rays such as X-rays and positrons into visible and ultraviolet light, are incorporated as radiation detectors in X-ray computer tomography (X-ray CT) and positron emission tomography (PET), which system performances highly depends on the characteristics of the scintillator used. In this study, SrGa2S4:Eu/ZnO vertical nanowires (ZnO-vnws) bilayer scintillators were fabricated by electrodeposition of ZnO-vnws followed by electrophoresis deposition of SrGa2S4:Eu particles, and their structure, optical properties, and scintillator characteristics were evaluated. The ZnO-vnws were composed of vertically aligned ZnO nanowires with an excellent (001) out-of-plane orientation, and the SrGa2S4:Eu layer was composed of particles adhered to the ZnO-vnws. The SrGa2S4:Eu/ZnO-vnws bilayer scintillators emitted visible light at a wavelength of 533 nm with a lifetime of 0.389 μs and functioned as a scintillator for X-ray irradiation. The resolution and luminescence intensity of the SrGa2S4:Eu/ZnO-vnws bilayer scintillators were improved by the introduction of the ZnO-vnws layer, when compared with those of the ZnO-vnws-free-SrGa2S4:Eu layer, when the thickness ratio of SrGa2S4:Eu layer to ZnO-nws length were 1.1 ∼1.3. The SrGa2S4:Eu/ZnO-vnws bilayer scintillator revealed a spatial resolution of 6.8 μm, which was slightly larger than 5.4 μm of a ready-made LuAG single-crystal scintillator.

Thin-film ZnO/Cu2O photovoltaic devices were prepared by electrochemical deposition in aqueous solutions, and significant improvements in the photovoltaic performances, especially external quantum efficiency (EQE), were achieved by rapid thermal annealing (RTA). ZnO were electrodeposited on Ga: ZnO-coated glass substrates from solutions containing zinc nitrate, and Cu2O were electrodeposited on the ZnO layer from solutions containing copper acetate and lactic acid. The photovoltaic performances were evaluated after annealing the ZnO/Cu2O layers at varying temperatures of 423–573 K under vacuum for 60 min, and a high EQE of nearly 100% was demonstrated by RTA at 423 K under vacuum. To elucidate the improvement effect of the RTA, structural characterizations were carried out with XRD and FESEM, and the optical and electrical properties were examined by UV–vis absorption spectroscopy and Hall effect measurements, respectively. The improvements in EQE was mainly attributed to the lessening of scattering defects in the light-absorbing Cu2O layer such as lattice dislocations and grain boundaries, which improved the charge collection efficiency. The photovoltaic performances deteriorated at elevated temperatures above 523 K due to the generation of small Cu particles on the Cu2O surface, which is associated with the generation of nanopores in the Cu2O bulk.

Electrochemical processes in aqueous solutions are widely used for preparation of metals, alloys, composites, metal oxides and compounds. For understanding and designing an electrochemical process, it is crucial to study its soluble chemical species, potential-pH diagram, and solubility curves drawn based on thermodynamics. In this review, equilibrium electrode potentials, critical pH values, and dissolved chemical species related to the oxidation-reduction, acid-base, and ligand-exchanging reactions, in addition to the calculation based on standard Gibbs free energy are first briefly mentioned. This is followed by the description of the change in equilibrium electrode potentials of metal and metal compounds as demonstrated in the electrochemical preparation of the Cu–In–Se precursor for the Cu(In,Ga)Se2 solar cell application. Additionally, the advantages and usefulness of soluble chemical species, potential-pH diagram, and solubility curves are discussed, by giving examples of direct electrodepositions of metal oxides, the chemical introduction of impurities into ZnO enabling characteristic control, the chemical bath deposition process (CBD) for Zn(S,O,OH) buffer layer in Cu(In,Ga)Se2 solar cell, and lastly, the design of the electrochemical process for fabricating CuO/Cu2O bilayers.

The copper oxides are best performing metal oxide materials regarding solar energy conversion, and due to their abundance, scalability, ease of fabrication and subsequently being low-cost, Cu2O and CuO have attracted extensive attraction. In this research, Cu2O layers were electrodeposited on Ga:ZnO (GZO) and annealed to form directly-stacked GZO/Cu2O/CuO. The external quantum efficiency (EQE) of the devices was evaluated which demonstrated peculiar negative regions around 500 nm besides the typical 410 nm originating from the Cu2O. Reversed bias voltages were applied to investigate the changes, and along with the disappearance of negative regions, a peak around 550 nm and an absorption edge at 850 nm appeared, which increased with the increment of bias voltage. To elucidate the mechanism, the electronic states were investigated by x-ray photoelectron spectra (XPS). Species identification was also successful which showed the presence of CuO on the topmost layer and the underlying Cu2O, which was difficult to analyze by XRD due to its thinness. The schematics of the band-alignments were drawn based on the calculations from the XPS measurements. The conduction band of the Cu2O appeared elevated, which contributed to the speculated two-way flow of the charge when illuminated, and explains the appearance of the negative EQE regions. The charge transportation was successfully controlled and aligned when bias voltages were applied, which caused the disappearance of negative regions and the appearance of the absorption edge of the CuO.

Cuprous oxide (Cu2O), a terrestrial abundant, low cost, nontoxic, intrinsically p-type oxide semiconductor with bandgap energy of about 2eV, has recently received increasing attention as a light absorbing layer in solar cells. However, the performances of electrochemically constructed Cu2O solar devices are poor compared to the theoretical power conversion efficiency. This research was conducted focusing on the EQE performance, which is closely related to the short circuit current of a solar device. ZnO/Cu2O-PV-devices were constructed electrochemically with 3-electrode cell on Ga:ZnO/SLG substrates; ZnO layers were deposited from an aqueous solution of 8 mmolL-1 zinc nitrate hexahydrate at 63°C, 0.01 Coulomb cm−2, and -0.8V, while Cu2O layers were deposited from aqueous solution containing 0.4 molL-1 copper (II) acetate monohydrate (pH12.5), at 40°C, 1.5 Coulomb cm−2, and -0.4V. Devices were then annealed under different temperatures of 150°C, 200°C, 250°C, and 300°C for 60 minutes with a Rapid Thermal A...

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/pssa.201700862