CdSe Electrodes Research Articles

CdSe electrochemical solar cells: the effect of ion surface treatments

Surface treatments of CdSe photoanodes may passivate grain boundaries or redistribute surface state energies. Cold-pressed CdSe electrodes were dipped for various lengths of time in cold or boiling ZnCl2 solution. The current-voltage characteristics and the dependence of the quantum efficiency on the applied forward bias were investigated and compared with the performance of untreated electrodes and electrodes dipped in HgCl2 solution. Zinc ion dipped photoanodes showed a pronounced increase in the solar performance because of an increase in the open-circuit voltage; mercuric ion dipped electrodes revealed a substantial decrease in the open-circuit voltage. The change in performance was much smaller for dipped cold-pressed CdSe electrodes than for electro-plated photoanodes.

Response to “Comment on ‘Adsorption of Hydroxide and Sulfide Ions on Single‐Crystal n ‐ CdSe Electrodes’” [J. Electrochem. Soc., 131, 2614

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Controlled photoelectrochemical etching of CdSe and observation of a photocathodic effect

Controlled photoetching of CdSe can be achieved by cyclic voltammetry in a partially stabilizing electrolyte, such as sulfite solution. By choosing the appropriate conditions for the photoetching such as concentration of the electrolyte and illumination intensity the semiconductor electrode is photoetched in the anodic half cycle, and the resultant oxidized layer of elemental Se is removed in the cathodic half cycle. The photocurrent of the CdSe electrode in 1 M sulfite solution increases gradually during the first hour of illumination under reverse bias conditions, with concomitant morphological changes similar to those previously observed for photoetched CdSe. The junction between CdSe/Se/sulfite exhibits a strong photocathodic effect which disappears after the Se top layer is carefully removed from the CdSe surface. The spectral response of the photocathodic current shows a strong peak at 740 nm under a bias of −1200 mV vs. SCE. It shifts slightly to the red and decreases in magnitude as the bias become even more cathodic. Possible mechanisms for this effect are discussed. It is suggested that the Se top layer shifts the flat band potential of the system in the positive direction (in accordance with previous results) thereby facilitating the creation of an accumulation layer which gives rise to the photocathodic effect. Auger microprobe analysis shows that most oxidized CdSe is released as elemental selenium rather than oxides, during photoetching. Thermodynamic data seem to support that observation.

Novel method for the preparation of nCdSe electrodes for photoelectrochemical cells

A new method for the preparation of nCdSe thin film electrodes which give a cell efficiency of 5.7% is presented. The band gap of the material deposited by this method was calculated and was found to be lower than the band gap reported earlier by various workers. The photoresponse is relatively constant over a wide range of wavelengths and it does not decrease at shorter wavelengths. The increase in the stability when the CdSe electrode is coated with a thin film of indium is also reported. The formation of CdSe on cadmium-plated nickel dipped in SeO 2 is a time-dependent process. The best fill factor and efficiency for a film of CdSe 2.4 μm thick are reported. The cadmium plating on nickel, the growth of CdSe films by dipping cadmium-plated nickel in SeO 2, the stability of the photoresponse and its dependence on the thickness of the CdSe film are described in detail. Finally the values of efficiency found in the present work are compared with reported values.

Photoelectrochemistry of CdSe in Sulfite Electrolyte

AbstractCyclic voltammetry is used to discriminate between two light induced reactions occurring on the surface of CdSe electrodes: Oxidation of the sulfite solution and self oxidation of the crystal itself. The latter reaction (photoetching) can be used to improve the performance of any photoelectrochemical cell based on CdSe as is shown here. The charge transfer of holes to the SO2‐3 electrolyte appears to be the rate determining step with photogenerated Se dissolution in the electrolyte playing an appreciable, but lesser, role. SO2‐3 ions are shown to adsorb weakly onto the surface of CdSe — a conclusion that supports a previous study. Thus, sulfite solutions are less favorable for use in a photoelectrochemical cells with CdSe but they can be used to carry out controlled photoetching of the CdSe electrode which leads to a reduction of the density of defects on the surface of that electrode and increases its surface area considerably.

Adsorption of Hydroxide and Sulfide Ions on Single‐Crystal n ‐ CdSe Electrodes

Flatband potentials were determined for (112̅0) electrodes as a function of OH− and SH− concentrations. Surface coverage was calculated from the observed flatband potential shift. The Frumkin isotherm was applied to the data, and thermodynamic parameters were determined. The standard free energies of adsorption for OH− and S= were found to be −2.3 and −6.9 kcal/mol, respectively. At high SH− concentrations, there was evidence for a decrease in the repulsive interactions of the S= and OH− ions.

Photoelectrochemical cells with mixed polycrystalline n-type CdSPbS and CdSCdSe electrodes

The photoelectrochemical behaviour of n-type CdS (polycrystalline) containing small amount of PbS or CdSe in S 2− /S 2− n redox system has been studied. Mixed polycrystalline n-type CdSPbS electrodes were prepared by electrodeposition and the n-type CdSCdSe electrodes were made by partial replacement of sulphide ions of CdS electrode with selenide ions from a solution of sodium selenosulphate. It has been observed that both the mixed chalcogenide electrodes exhibit better photoresponse than the simple CdS electrode.

Electroluminescence of Polycrystalline CdSe Thin Film Photoelectrodes: A Sensitive Probe for Surface Recombination

not Available.

Improved performance of cadmium chalcogenide photoelectrochemical cells: surface modification using copper sulphide

The effect of copper sulphide species on the photoactivity of cadmium chalcogenide photoelectrodes is discussed. This species, believed to be CuS, is applied using two methods. In the first, polished CdSe electrodes are dipped into a solution containing cupric ions, immersed in polysulphide solution and subsequently operated as anodes. In the latter technique, copper species migrates from a sulphided, brass counter electrode to an etched CdSe or CdSexTe1-x photoelectrode. In the former case, the main effect of the copper treatment is an increase in the short-circuit photocurrent while in the latter case, the dark cathodic current decreases and the open-circuit voltage increases. The effect of these treatments is explained by preferential deposition of copper (or some copper-containing species) at surface defect sites, resulting in the partial passivation or blocking of these sites.

Chalcopyrite-type ternaries as photoelectrodes in wet solar cells

The performance of photoelectrochemical cells, containingn-CuInX2 (X=S, Se) semiconductor electrodes, has been studied as a function of solution composition and temperature. Significant differences with cells using CdSe or CdIn2Se4 electrodes are found, also in terms of output stability. These results, together with surface analyses, suggest the occurrence of binary chalcogenides on the electrode surfaces, which seems to influence the behaviour of these cells favourably

Fluorescent window as wavelength shifter for a polysulfide containing photoelectrochemical cell

It is possible to obtain a gain in conversion efficiency of a photoelectrochemical cell by the use of a fluorescent wavelength shifter. If the dye is chosen in such a way that its adsorption and fluorescence spectrum fits the photocurrent onset of the cell, gains in efficiency can be found. By the use of fluoresceine in methanol solutions as the shifter and a polysulfide electrolyte, gains of up to 6% can be obtained with a CdSe 0.65Te 0.35 electrode and up to 10% with a CdSe electrode. The effect is also observed when using plastic sheets, doped with the dye. If the dimensions of the sheet exceed those of the cell an appreciable concentrating effect is also observed. These effects are found either with a xenon light source or with direct sunlight and are not corrected for constant quantum flux. With light which is richer in low wavelength radiation, much higher gains are obtained which is important for the concentration of diffuse light. Uranyl doped glass gives also shifting effects, but these are too small to give a measurable gain in efficiency. The conclusion is drawn that it is not so much the small Stokes shift of an organic dye, which prevents its use for this purpose, but its instability. The stable inorganic ions on the other hand, do not absorb sufficient light, because of their low oscillator strength.

Localized Photoprocesses at Semiconductor-Electrolyte Interfaces Using a Programmable Laser Spot Scanner

ABSTRACTA highly focused laser can be used to perform spatially selective photoelectrochemistry at semiconductor-electrolyte interfaces. These processes may be used for imaging (etching, deposition, etc.) or for nondestructive mapping of semiconductor properties from photoelectric response. A programmable laser scanner is described which can be used for both. An example of imaging is given for photoelectrochemical etching of pits in CdSe electrodes, which may be applied to archival data storage. Nondestructive evaluation is shown for a CdS crystal, in which the lateral distribution of subband gap photovoltage response is related to surface states incurred by polishing damage.

Optimising the photoelectrochemical performance of electrodeposited CdSe semiconductor electrodes

The effects of deposition potential on the performance of CdSe electrodes in CdSe-based PEC cells have been determined at 40°C. An optimum deposition potential range was determined. A 4.24% efficient CdSe PEC cell was constructed using a CdSe thin-film electrode deposited in the optimal potential range. Several post-annealing treatments for enhancing the performances of CdSe thin-film electrodes are described.

The Mechanism of Photocatalysis on Semiconductor Powders in a Liquid Medium. New Experimental Methods and Their Results

AbstractTwo new methods are described for following the reactions occurring on semiconductor powders, when illuminated in a solution of reactants. The reaction between nitroaromatics and hydrazine gives gaseous nitrogen as one of the products, which can be measured manometrically. The rate with CdSe as the catalyst is strongly dependent on the structure of the nitroaromatic, giving faster reactions for the better electron acceptors. The more polar the solvents the lower the yields. The reaction between K4Fe(CN)6 and air in aqueous solution is measured by electrochemical reduction of the product K3Fe(CN)6. Rates are strongly dependent on heat treatments given to the semiconductor before reaction and the dependence of rate on CdSe heat treatment is very similar for both the nitrobenzene/hydrazine reaction in methanol and the K4Fe(CN)6 oxidation in water. Electrochemical measurements with CdSe electrodes in benzene show the current onset to be at a potential similar to the first reduction potential of the nitroaromatics used, which explains the strong rate dependence on the reduction potential of the nitroaromatic. A mechanism is proposed for the n‐type case of a rapid reaction occurring between the minority carriers and hydrazine, by which the powder charges up negatively and the electron transfer from the charged powder to the nitroaromatic in solution is rate determining. With p‐type semiconductors, which give slower rates, the minority carrier reaction with the nitroaromatics is rate determining and only little positive charge accumulates on the particles.

Role of Disorder in Photoelectrochemical Solar Cells with Polycrystalline Photoanodes

This paper reports measurements of electrical impedance versus frequency on photoelectrochemical solar cells and metal-insulator-semiconductor junctions using polycrystalline, electrodeposited $n$-CdSe electrodes. A simple power law in frequency for the photoelectrochemical cell impedance is interpreted in terms of a percolation conduction at the semiconductor-electrolyte interface with use of arguments supported by measurements on this and related systems.

An economic analysis of photoelectrochemical cells

The economic viability of photoelectrochemical cells is examined for two representative systems based on n-type GaAs and n-type CdSe electrodes in contact with aqueous polyselenide and polysulfide electrolytes respectively. Cell fabrication costs for these systems are compared with a test case comprising a sequence of processes in a typical fabrication of silicon p-n junction solar cells. A standardized methodology based on the solar array manufacturing industry costing standards improved price estimation guideline is employed for the comparison. Under the framework of assumptions implicit in this analysis, photoelectrochemical systems emerge as a viable cost-competitive option to silicon p-n junction solar cells. The sensitivity of the computed cell costs to parameters such as cell efficiency and material costs is discussed.