Masanobu Izaki

TRANSPARENT ZINC OXIDE FILMS PREPARED BY ELECTROCHEMICAL REACTION

Transparent zinc oxide (ZnO) films has been cathodically deposited on conductive glasses from a simple aqueous zinc nitrate electrolyte kept at 335 K. ZnO films prepared had a wurtzite structure and exhibited an optical band gap energy of 3.3 eV which is characteristic of ZnO. A 2‐μm‐thick ZnO film with an optical transmittance of 72% has been deposited by electrolysis only for approximately 20 minutes at the cathodic potential of −1.0 V compared with the Ag/AgCl reference electrode.

Electrochemically constructed p-Cu2O/n-ZnO heterojunction diode for photovoltaic device

Polycrystalline n-ZnO/p-Cu2O heterojunctions have been fabricated by low-temperature eletrodepositions of ZnO and Cu2O layers in aqueous solutions. The condition for forming the Cu2O layer significantly reflected the electrical rectification characteristic and the photovoltaic performance, and the heterojunction fabricated under optimized conditions showed an excellent electrical rectification characteristic and a photovoltaic performance of 1.28% in conversion efficiency under an AM 1.5 illumination.

Electrolyte Optimization for Cathodic Growth of Zinc Oxide Films

Zinc oxide is of considerable interest to the optical and electronic industries, because of its electrical, optical, and acoustic characteristics. ZnO films can be prepared by several techniques, such as radio frequency (RF) magnetron sputtering, chemical vapor deposition, and molecular beam epitaxy. Preparation of oxide films by electrodeposition from aqueous solutions has several potential advantages over the other techniques. However, the formation of oxide films through electrochemical reactions have been demonstrated only on thallic oxide by Switzer and zirconium oxide by Gal-Or. In this work, the authors have prepared transparent ZnO films with optical bandgap energy of 3.3 eV by electrodeposition from an aqueous, 0.1 mol/liter zinc nitrate electrolyte. The deposition technology is still being developed. This paper reports the effects of the electrolyte concentration on the electrodeposition and properties of the ZnO films.

Characterization of Transparent Zinc Oxide Films Prepared by Electrochemical Reaction

Transparent zinc oxide (ZnO) films have been grown by galvanostatic cathodic deposition onto conductive glasses from a simple aqueous zinc nitrate electrolyte maintained at 335 K. The as-deposited ZnO films were characterized with Fourier transform infrared absorption spectroscopy, x-ray diffraction, scanning electron microscopy, optical transmission and absorption studies, and measurement of sheet resistivity as a function of cathodic current density. The ZnO films prepared had a wurtzite structure and exhibited an optical bandgap energy of 3.3 eV which is characteristic of ZnO. At a low cathodic current density of 0.05 mA/cm{sup 2}, ZnO films with excellent electrical characteristics have been obtained. A 2 {micro}m thick ZnO film with an optical transmittance of 72% was deposited by electrolysis for approximately 20 min at a cathodic current density of 10 mA/cm{sup 2}.

Transparent Zinc Oxide Films Chemically Prepared from Aqueous Solution

Transparent zinc oxide (ZnO) films had been chemically deposited on nonconductive glass from aqueous solutions containing zinc nitrate and dimethylamine-borane (DMAB) kept at 323 K. The ZnO films had a wurtzite structure and exhibited an optical bandgap energy of 3.3 eV which is characteristic of ZnO. A 0.2 μm thick ZnO film with an optical transmittance of 80% was deposited by immersion for approximately 20 min in an aqueous solution containing 0.05 mol/liter zinc nitrate and 0.05 to 0.1 mol/liter DMAB.

Structural and Electrical Characterizations of Electrodeposited p-Type Semiconductor Cu2O Films

The p-type semiconductor cuprous oxide (Cu 2 O) film has been of considerable interest as a component of solar cells and photodiodes due to its bandgap energy of 2.1 eV and high optical absorption coefficient. We prepared Cu 2 O films on a conductive substrate by electrodeposition at 318 K from an aqueous solution containing copper sulfate and lactic acid. The structural and electrical characterizations of the resulting films were examined by X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption measurements, and the Hall effect measurement, respectively. The resistivity varied from 2.7 × 10 4 to 3.3 X 10 6 Ω cm, while the carrier density was from 10 1 2 to 10 1 4 cm - 3 and the mobility from 0.4 to 1.8 cm 2 V - 1 s - 1 , depending on the preparation conditions, i.e., solution pH and deposition potential. The carrier density was sensitive to the atomic ratio of Cu to O in the films and the mobility to the grain size.

Preparation of Manganese Oxide Thin Films by Electrolysis/Chemical Deposition and Electrochromism

Manganese oxide (MnO 3 ) thin films were deposited onto transparent and conductive tin oxide-coated glass substrates by electrochemical deposition (at 1.2 V vs. Ag/AgCl) and subsequent chemical [electrolysis/chemical (EL/C)] processing in a manganese ammine complex solution at pH 8. Characterization by X-ray diffraction (XRD) of the films revealed that the crystal structure formed in the films by EL/C deposition is assigned to γ-Mn 2 O 3 and/or Mn 3 O 3 . X-ray photoelectron spectroscopy (XPS) was also performed to focus on exchange splitting effect shown in Mn 3s spectra and peak analyses of O Is spectra of the films. From electrochemical, quartz crystal microbalance, XRD, XPS, and atomic force microseope studies, a mechanism of film growth was illustrated, featuring time course of rest potential during chemical process. The XPS data also suggested that the electrochromic behavior, turning brown and light yellow by the anodic and cathodic polarization in potassium borate buffer solution at pH 10. originates from a transformation between two oxygen groups in hydroxide (Mn-O-H) and oxide (Mn-O-Mn) accompanied by the change in valence of Mn. The repeated EC switching performance of the films was also assayed.

Characterization of Boron‐Incorporated Zinc Oxide Film Chemically Prepared from an Aqueous Solution

Boron-incorporated ZnO film which had a wurtzite structure and showed optical bandgap energy of 3.3 eV was prepared chemically onto a nonconductive substrate by immersing the substrate in an aqueous solution containing a zinc nitrate and dimethylamineborane (DMAB) at 333 K. Effects of the incorporated boron on the structural, optical, and electrical characteristics of ZnO film were investigated using X-ray diffraction, evaluation of surface morphology with an atomic force microscope, measurements of optical transmission spectra, and Hall measurement. Small amounts of boron atoms, which originated from the DMAB, were incorporated into ZnO grain and gave the lattice expansion. A pore-free ZnO film with a smooth surface was obtained from the 0. 1 mol/L DMAB solution. The ZnO film showed optical transmission as high as 80% in the visible light region and resistivity of 3.6 × 10 2 Ω cm with carrier concentration of 1.7 × 10 16 cm -3 and mobility of 1.0 cm 2 V -1 s -1 . It was speculated that the incorporated boron atom acted as a donor in the ZnO film.

Cu2SnS3 thin-film solar cells fabricated by sulfurization from NaF/Cu/Sn stacked precursor

Cu2SnS3 thin films were prepared by crystallization in a sulfur/tin mixing atmosphere from stacked NaF/Cu/Sn precursors deposited by the sequential evaporation of Sn, Cu elements, and NaF. The NaF mole ratio was changed at (x = 0 to 0.12). From X-ray diffraction patterns and Raman spectra, the Cu2SnS3 thin films were considered to have a monoclinic structure. The grain size of the Cu2SnS3 thin films decreased with increasing NaF/Cu mole ratio. The band-gap energies of the Cu2SnS3 thin films determined from quantum efficiency spectra were 0.93 and 1.02 eV. The solar cell with x = 0.075 demonstrated the best performance, namely, Voc = 283 mV, Isc = 37.3 mA/cm2, FF = 0.439, and ? = 4.63%.

Preparation of transparent and conductive zinc oxide films by optimization of the two-step electrolysis technique

The two-step electrolysis technique was developed for the purpose of preparation of a transparent and conductive zinc oxide (ZnO) film by cathodic deposition from a simple zinc nitrate aqueous solution at ambient temperature. The structural, optical, and electrical characterizations were performed with an atomic force microscope, scanning electron microscope, reflection high-energy electron diffraction, X-ray diffraction, measurements of optical transmission and absorption spectra, and Hall measurement. The purpose was achieved by using a two-step electrolysis consisting of first-step electrolysis at - 1.2 V referred to an Ag/AgCl electrode for electric charge of 0.03 C cm -2 and of second-step electrolysis at -0.7 V. The first-step electrolysis gave homogenous deposition of ZnO particles over an entire substrate surface. During the second-step electrolysis the ZnO particles grew normal to the substrate surface, and the resultant ZnO film did not contain any defects such as pores and showed smooth surface. The ZnO film showed high optical transmission of about 80% in the visible light region and resistivity as low as 4 × 10 -3 Ω cm with 6.5 × 10 19 cm -3 carrier concentration and 23.7 cm 2 V -1 s - 1 mobility.