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Au/n‐WSe2 Schottky junctions usually exhibit linear dark current‐voltage characteristics, apparently dominated by structural defects, and low open circuit photovoltages. After treatment of the WSe2 with polyiodide in a liquid junction configuration and subsequent deposition of Au, good diode characteristics and high Voc are obtained which are similar to those exhibited by WSe2/polyiodide liquid junctions. The role of the polyiodide treatment is ascribed to defect passivation. The barrier height of the WSe2/Au junction (∼1.0 eV) is particularly high for a semiconductor of Eg=1.2 eV and supports recent work which claims that MoS2 (similar structure to WSe2) forms Schottky junctions which behave close to the Schottky limit.

High efficiency (12.7%) CdSe0.68Te0.32/cesium polysulfide photoelectrochemical cells are demonstrated in this work. Crystals of the ternary alloy Cd(Se, Te) of type n type were synthesized by the traveling heater method. The nature of the polysulfide electrolyte, based on Cs polysulfide without excess hydroxide and containing small amounts of copper ions, is shown to be of particular importance in determining the cell efficiency. Reasonable output stability of the cell was obtained under accelerated tests.

Thin-film polycrystalline Cd(Se,Te) alloy photoelectrodes, which show output stability comparable to CdSe photoelectrodes when possessing the hexagonal (wurtzite) structure and which have optical band gaps similar to that of pure CdTe, are discussed.

By illuminating a CdSe photoanode in an electrolyte in which it is photoelectrochemically unstable, a selective etching of the CdSe to a matte black surface occurs with formation of small pits (≈1000 A diameter). This photoelectrochemical etch was found to improve the output characteristics of the CdSe‐polysulfide photoelectrochemical cell through an increase in short‐circuit current (SCC) for single‐crystal CdSe, and an increase in fill factor and SCC for polycrystalline CdSe, where the improvement is more marked. This increase could be explained only partly through decreased reflectivity of the surface, and is probably connected with removal of (near) surface recombination centers.

Parallel secondary electron and charge collection images of a CdS/Au Schottky barrier show that photoetching of the CdS improves the charge collection efficiency. This is explained in terms of preferential removal of (near) surface recombination centers by the photoetching. Evidence is given that lack of photoetching of specific areas of the surface is due to the fact that such areas are photoelectrochemically inactive, possibly because of poor electrical contact with underlying CdS, and combined photoetching and scanning electron microscopy investigation is suggested as a way to check semiconductors for inactive regions.

Die Eigenschaften einer photoelektrochemischen Zelle auf der Basis von n-leitendem (in einer Gluhentladung abgeschiedenem) amorphem hydriertem Si (a-Si:H) mit dem nichtwasrigen Elektrolytsystem Ferrocenium/Ferrocen in Ethanol werden mit denen einer entsprechenden Zelle mit kristallinem Si (c-Si) verglichen.

Optical band gaps, ${E}_{g}$, up to 0.5 eV higher than in single-crystal samples, are observed for chemically deposited films of CdSe and explained in terms of a quantum-size effect, whereby the electrons are localized in individual crystallites. The increase in ${E}_{g}$ depends strongly on deposition temperature, with the greatest increase obtained at the lowest temperature. Annealing at temperatures above the deposition temperature causes a decrease in ${E}_{g}$; this decrease is stronger at higher annealing temperature. Structural studies of the as-deposited layers showed them to be composed of microcrystalline, cubic CdSe, and electron microscopy resolved them into individual crystallites of typically 40--80-A\r{} diameter, depending on deposition temperature. This is the first example reported of a three-dimensional quantum-size effect in a film.

THE PEC1 has acquired popularity among researchers in the past years, mainly because of its possible use in solar energy conversion2,3. The major problem at present is to find a semiconductor electrode with an optical band gap (written as just band gap below) small enough to allow it to absorb a reasonably large portion of the solar spectrum, and at the same time being stable against photocorrosion. We here report that WO3 meets these criteria although it is not very efficient at solar wavelengths.

Die Eigenschaften einer photoelektrochemischen Zelle auf der Basis von n-leitendem (in einer Gluhentladung abgeschiedenem) amorphem hydriertem Si (a-Si:H) mit dem nichtwasrigen Elektrolytsystem Ferrocenium/Ferrocen in Ethanol werden mit denen einer entsprechenden Zelle mit kristallinem Si (c-Si) verglichen.

Utilisation de la methode iterative sur ordinateur pour calculer les differentes especes dans des solutions aqueuses de polysulfures de metaux alcalins, comprenant OH − ,H + ,H 2 S,HS − ,S 2− ,S 2 2− ,S 3 2− ,S 4 2− ,S 5 2− , eau et cations de metal alcalin. Calcul de la distribution de ces 11 especes chimiques dans les solutions susceptibles d'etre utilisees comme electrolytes dans des piles photoelectrochimiques

A simple, versatile method for fabricating semiconductor layers for use as photoelectrodes in photoelectrochemical cells is described. This method, in which a slurry of the semiconductor is painted onto a substrate, is demonstrated particularly for Cd (and Zn) chalcogenides, but is shown to be applicable to other materials of photovoltaic interest, such as . Also, the method allows for simple fabrication of layers of solid solutions, such as cadmium mixed chalcogenides.

CdS and CdSe films electrodeposited from chalcogen-containing non-aqueous electrolytes are shown to possess a nanocrystalline structure and exhibit 3-D quantum size effects. A large variation in optical transmission spectra, due for the most part to this sizequantization, is shown. Photoelectrochemical activity of the as-deposited films is discussed in terms of their nano-structure. Extension of the crystallite size effects to a metalinsulator transition in MoO2 deposited from a similar electrolyte is mentioned.

Porous electrocatalytic electrodes for the polysulfide redox system, containing one of various metallic sulfides (especially of Co, Cu, Pb) are described. Emphasis is placed on their use as counterelectrodes in photoelectrochemical cells employing polysulfide electrolytes. Their activity is measured as a function of electrolyte temperature and composition. The ratio of S to S2−, and through it the local redox potential of the solution, is shown to be an important factor controlling electrode activity. The short and long term stability of the electrodes, as cathodes, is discussed, and it is shown that, when used in conjunction with photoanodes, and may poison the photoelectrode surface, thereby reducing total cell efficiency.

The importance of solution effects for photoelectrochemical performance is discussed at the hand of experiments done at photoelect-rodes. The solution composition is shown to be of crucial importance for photoelectrochemical behavior and the significance of this for photocatalytic phenomena is discussed.

Hysteresis in the current-voltage characteristics of hybrid organic-inorganic perovskite-based solar cells is one of the fundamental aspects of these cells that we do not understand well. One possible cause, suggested for the hysteresis, is polarization of the perovskite layer under applied voltage and illumination bias, due to ion migration within the perovskite. To study this problem systemically, current-voltage characteristics of both regular (light incident through the electron conducting contact) and so-called inverted (light incident through the hole conducting contact) perovskite cells were studied at different temperatures and scan rates. We explain our results by assuming that the effects of scan rate and temperature on hysteresis are strongly correlated to ion migration within the device, with the rate-determining step being ion migration at/across the interfaces of the perovskite layer with the contact materials. By correlating between the scan rate with the measurement temperature, we show that the inverted and regular cells operate in different hysteresis regimes, with different activation energies of 0.28 ± 0.04 eV and 0.59 ± 0.09 eV, respectively. We suggest that the differences observed between the two architectures are due to different rates of ion migration close to the interfaces, and conclude that the diffusion coefficient of migrating ions in the inverted cells is 3 orders of magnitude higher than in the regular cells, leading to different accumulation rates of ions near the interfaces. Analysis of VOC as a function of temperature shows that the main recombination mechanism is trap-assisted (Shockley-Read Hall, SRH) in the space charge region, similar to what is the case for other thin film inorganic solar cells.

We explain the cause for the photocurrent and photovoltage in nanocrystalline, mesoporous dye-sensitized solar cells, in terms of the separation, recombination, and transport of electronic charge as well as in terms of electron energetics. On the basis of available experimental data, we confirm that the basic cause for the photovoltage is the change in the electron concentration in the nanocrystalline electron conductor that results from photoinduced charge injection from the dye. The maximum photovoltage is given by the difference in electron energies between the redox level and the bottom of the electron conductor's conduction band, rather than by any difference in electrical potential in the cell, in the dark. Charge separation occurs because of the energetic and entropic driving forces that exist at the dye/electron conductor interface, with charge transport aided by such driving forces at the electron conductor/contact interface. The mesoporosity and nanocrystallinity of the semiconductor are importa...

Photovoltaic effects in CdSe quantum dot (QD) films have been studied using surface photovoltage spectroscopy and complementary methods. The results show that, contrary to previous studies, nonnegligible electric fields can exist in QD films. As a result, driftlike currents must be considered, in addition to the well-known diffusion like currents. However, it is found that the specific case of photovoltage sign reversal, observed after etching highly quantized CdSe QD films, is governed by diffusion like transport. The latter is highly influenced by preferential trapping of one type of charge carrier. The preferential trapping is shown to be surface localized and is strongly ambient dependent. It is shown that the photovoltaic properties of these CdSe QD films are dominated by their surface state distribution.

The role of Cu in CdTe/CdS solar cell instability remains the subject of much debate. The investigation of a range of ‘Cu’-contacted CdTe/CdS cells, which had received various thermal stress treatments, is described. Cells that were stressed in air exhibit strong current-voltage (I-V) rollover and junction degradation. No such degradation was observed for ‘Cu’-contacted cells that had been stressed in dry-N2 atmosphere. Cu is found to diffuse rapidly through the cell structure during back contact annealing and to accumulate in the CdS layer. With stress, significant levels of Cu dope the grain bulk, producing (with Cl) high resistance, photoconducting CdS. This behavior is independent of stress atmosphere and is, therefore, unlikely to (initially) be a dominating mechanism for cell degradation. Our results suggest simple air oxidation of the back contact interface to be a likely origin of I-V rollover in CdTe/CdS cells.

WE report here on a major improvement in the conversion efficiency of corrosion-free photoelectrochemical cells (PECs) and on a novel extension of such cells which allows the storage of part or all of the converted energy in situ for subsequent use.

We report a photoelectrochemical solar cell (PEC) with in situ storage, operating at 11.3% overall solar to electrical conversion efficiency, with a generated power insensitive to daily fluctuations in solar radiation. A primary advantage of PECs, compared to photovoltaic solar cells, had been their proposed capacity for in situ storage by the addition of a single electrochemical half cell1. Several systems combining photoelectrochemical conversion with electrochemical storage have been presented with maximum efficiencies of approximately 3 per cent. A series of polysulphide solution effects2–5 resulted in a high efficiency caesium polysulphide n-Cd(Se,Te) single crystal PEC6. As will be shown, this leads to an autonomous cell with sufficient voltage to bypass the previous necessity for bipolar dual photoelectrode storage, allowing single photoelectrode induced electrochemical storage, with a high continuous output.

We show that the oxygen content of YBa 2 Cu 3 O 7−x can be reduce at room temperature by using electrochemical techniques. The products have been characterized by x-ray powder diffraction, electrical resistivity, and magnetic susceptibility. The reduced material shows a broadened transition to the superconducting state.

Photoelectrochemical solar cells (PECs) may become an economic method for conversion of light to electricity, due largely to the simplicity of formation, and quality, of the poly-crystalline semiconductor–electrolyte junction. Within the past few years, conversion efficiencies of thin-layer poly crystalline-based cells have increased from ∼1% to a recently reported 7.3% for the n-GaAs/Sex2− system1. PECs based on the CdSe–polysulphide system have been studied extensively recently. CdTe, with a band-gap, Eg, ∼1.45 eV is better matched to the solar spectrum than CdSe (Eg∼1·75 eV), but is unstable in polysulphide solutions as a photoanode at the current densities to be expected under normal solar irradiation (>10 mA cm−2). A poly sulphide-based PEC is described here which uses poly-crystalline layers of CdSe0.65Te0.35, electrodes of which are prepared by painting a slurry of the semiconductor onto a T1 substrate, and sintering. Subsequent surface treatments of these layers lead to a solar-to-electrical conversion efficiency of up to 8%, with stability comparable to the thin-layer polycrystalline CdSe/polysulphide system2.