Yasusada Ueno

Electrophoretically Deposited CdS and CdSe Anodes for Photoelectrochemical Cells

The electrophoretic deposition of CdS, CdSe, and their mixtures has been studied for the preparation of thin film anodes for photoelectrochemical cells. These films were obtained in a homogeneous state on SnO/sub 2//sup -/ coated glass substrates from the suspensions using polar organic dispersion media. Prior to photoelectrochemical experiments, the thin film anodes were thermally treated for 3 hr at 400/sup 0/-600/sup 0/C. An energy conversion efficiency of 2% was observed for the photoelectrochemical cells using these film anodes in S/sup 2 -//S /SUB lx/ /sup 2 -/ electrolytes.

Electrochemical solar cell based on a sprayed CdS film photoanode

Electrochemical studies of the CdS film deposited onto a transparent conductive SnO2-coated glass slide by chemical spray deposition were performed in aqueous polysulphide solutions and the output characteristics of the electrochemical photocell (sprayed CdS film/polysulphide electrolyte/Pt) were measured. It was proved to be possible to construct a regenerative photocell free from the light losses through the polysulphide solution path by illuminating the CdS film anode through the SnO2-coated glass. Quantum yield and the maximum energy conversion efficiency of this photocell for monochromatic excitation of 480 nm were about 8% and 0.5%, respectively. It is concluded that the poorer quantum yield of this photocell employing CdS film than that of a photocell employing single crystal CdS can be attributed to the existence of lattice imperfections in the film.

Photochargeable multilayer membrane device composed of CdS film and prussian blue battery

Photoenergy conversion and storage are attracting attention not only in solar energy utilization but also in photodevices which are important for the future socalled photonics (photoelectronics). Photoinduced charge separation and the following accumulation of the separated charges are typical processes in photoenergy/information conversion and storage. These processes are generally carried out in different systems or phases respectively to result in a whole achievement. If they are combined to realize in one device, it must be of much value for the development of photodevices. Such a device is capable of photocharge and dark-discharge, and would open a new field in photoenergy and information conversion/storage. Some systems for photocharge and dark-discharge have been reported that are composed of liquidjunction semiconductor and redox electrolyte present in solution[l-51. A new concept is now proposed to realize photocharge and dark-discharge by a multifunctional solid state device, which must be of great use for practical application. The present authors have designed a multilayer membrane device for photocharge and dark-discharge so that each layer bears a function such as photoinduced charge separation, accumulation of positive/negative charges, separation of reactants. As for the membrane materials, polymer is most suited for practical use[6]. As a charge storage material, Prussian Blue (PB) which is a high molecular and polynuclear mixedvalent iron cyanide complex was chosen in the present paper. Electrochemical behavior of PB has been well characterized by Neff and Itaya et aI.[7-91. This complex, whose composition is represented by Fe:’ [Fe”(CN),]:-, has three kinds of reversible redox states, so that it can store both positive and negative charges. PB batteries were reported by NefllO], Kanekorll, 123, and Honda et al.[13] in which two PB films were utilized for an anode and a cathode. A multilayer PB polymer battery (PB/Nafion/PB) has been fabricated, and its reaction characteristics have been studied electrochemically and spectrophotometrically by the present authors[12]. Photoreaction of PB film coated on TiO, has been studied in aqueous electrolyte solution[14], but this system uses only ultraviolet light and dark-discharge has not been reported. In the present paper, a multilayer solid type photochargeable device driven by visible light irradiation will be reported which is composed of n-CdS semiconductor film and trilayered PB battery membranes.

Crystal growth of cadmium selenide by fused salt electrolysis and its photoelectrochemical properties

Abstract The electrodeposition of CdSe crystals has been examined under potentiostatic condition on graphite electrodes in LiClKCl melts containing CdCl 2 and Na 2 SeO 3 . Deposits with various morphologies, needle-like, hollow-like, dendritic and columnar crystals, have been obtained by controlling the deposition potential. These as-grown deposits have fairly good photoelectrochemical characteristics and photoelectrochemical cells with a maximum conversion efficiency of 6.1% under white light illumination of 37 mW/cm 2 were constructed using a CdSe photoanode.

Synthesis of Cu‐In‐S Compounds and Their Photoelectrochemical Characterization

The authors describe three different compounds in the pseudobinary Cu/sub 2/S-In/sub 2/S/sub 3/ system, namely, CuInS/sub 2/, CuIn/sub 5/S/sub 8/, and CuIn/sub 11/S/sub 17/, synthesized selectively in high yields by using the homogeneous precipitation technique. This process consists of the formation of (Cu/sub 2/S)/sub x/(In/sub 2/S/sub 3/)/sub 1-x/ precipitates from a Na/sub 2/S/sub 2/O/sub 3/ solution containing different quantities of CuCl/sub 2/, InCl/sub 3/, and CH/sub 3/COOH and the subsequent firing of the resulting precipitates at 600{sup 0}C. Polycrystalline n-CuIn/sub 5/S/sub 8/ and n-CuIn/sub 11/S/sub 17/ electrodes prepared in the form of sintered pellets exhibit anodic photocurrents of ca. 16 mA/cm/sup 2/ under 100 mW/cm/sup 2/ white light irradiance. Bandgaps have been determined to be 1.45 eV (direct) and 1.26 eV (indirect) for CuIn/sub 11/S/sub 17/, 1.40 eV (direct), 1.13 eV (indirect) for CuIn/sub 5/S/sub 8/, and 1.50 eV (direct) and 1.24 eV (indirect) for CuInS/sub 2/. Energy conversion efficencies as high as 3.3-3.4% have been obtained for n-CuIn/sub 5/S/sub 8-/ or n-CuIn/sub 11/S/sub 17-/ based cells under white light illumination of 100 mW/cm/sup 2/.

Chemical bath precipitation of CdSe particles for use in a photoelectrochemical cell

Abstract A simple synthetic procedure for CdSe particles was investigated for use in photoelectrochemical applications. The particles obtained by the homogeneous precipitation reaction between selenosulfite and cadmium hydrated or ammine complex ions were thermally treated and then used as photoanode materials in photoelectrochemical cells (PECs). For the resultant cell, energy conversion efficiencies of 4–8% were obtained under white light illumination of 50 mW/cm2.

Photoelectrochemical Properties of Polycrystalline Films of CdS Doped with Cu

The authors describe photoelectrochemical properties of polycrystalline, photoconductive CdS electrodes doped with Cu studies with particular emphasis on the role of Cu impurity level. They exhibit both anodic photocurrent and cathodic photocurrent of considerably high values. They found by voltammetric and spectral response experiments that the light absorption by the Cu level contributes to pronounced cathodic photoresponse arising from their photoconductivity and significant red shift in spectral response for anodic photocurrent up to 820 nm. Both these observations are novel as far as CdS-based phottoelectrochemical configurations are concerned. Furthermore, quantum efficencies exceeding 0.2 for the anodic photocurrent in the red shift region have been obtained. All these results can be reasonably explained by considering photoeffects associated with Cu impurity in CdS.

Synthesis and photoelectrochemical characterization of (Ag2S)x(In2S3)1−x and AgInS2−ySey

Abstract Ternary n-type AgInS2 and AgIn5S5 have been synthesized selectively by homogeneous precipitation from an aqueous solution containing the prescribed amounts of AgNO3, In2(SO4)3, Na2S2O3 and CH3COOH followed by heat treatments of the resulting precipitates at 500–800°C. Quaternary n-type AgInS2−ySey semiconductors were also synthesized by sintering of a mixture of as-precipitated AgInS2 and elemental Se. Photoelectrochemical characterization of these semiconductors was studied using the photoanodes prepared in the form of sintered pellets in a polysulfide electrolyte. Compared with the relatively poor saturated photocurrent for AgInS2 (0.7 mA/cm2) and AgIn5S8 (0.01 mA/cm2, AgInS1.5Se0.5 photoanode exhibits a higher photocurrent (20 mA/cm2) under 100 mW/cm2 white-light illumination. This effect has been ascribed to the development of a highly oriented chalcopyrite crsytal during the sintering process at 800°C for 2 h. The chalcopyrite is a solid solution of AgInS2 and AgInSe2 and has band gaps between those of AgInS2 and AgInSe2. An energy conversion efficiency of 0.55%, a fill factor of 0.40, and a Voc of 0.23 V has been obtained for the oriented quarternary photoanode.

Microscopic observation of electrodeposition sites of Tl2O3 at n-type CdSe electrode

Abstract The deposition site selectivity of Tl2O3 on CdSe surfaces with well defined crystallographic orientations has been investigated. It was found that under illumination anodic deposition of Tl2O3 and its cathodic dissolution on a polycrystalline and a single crystal electrode took place reversibly in a Tl+ ion containing solution. This deposition reaction was promoted by photogenerated holes and occurred uniformly on the grain surface except on the (0002) face. In the dark, the deposition of Tl2O3 only occurred on the polycrystalline electrodes, and no deposition occurred on single crystal electrodes. SEM observation showed that the deposition reaction took place selectively at the grain boundaries and Tl2O3 deposited on the grain boundaries did not cathodically redissolve.

Photoelectrochemical analyses of photocatalytic reactions of azobenzene on TiO2 powder

Abstract Photoelectrochemical processes in the formation of 2-phenylindazole from 4-methoxyazobenzene with powdered TiO 2 photocatalyst in methanolic solution has been analyzed by using a TiO 2 film electrode under controlled potentials. The experimental facts that the reaction yields depend strongly upon the electrolytic potential and are quite high only under weak anodic polarization (weak upward band bending) suggest that electrons as well as positive holes participate in the formation of 2-phenylindazole cooperatively, which confirms our assumption for the reaction mechanism reported earlier. The results demonstrate that the photoelectrochemical techniques serve as a useful tool for clarifying photocatalytic processes in the organic synthesis occurring on illuminated semiconductor powders.