Solar energy, conversion photoelectrochemical cells

Nakato, Y., Ueda, K., Yano, H., and Tsubomura, H., Effect of microscopic discontinuity of metal over layers on the photo voltages in metal-coated semiconductor-liquid junction photoelectrochemical cells for efficient solar energy conversion, /. Phys. Chem., 92, 2316, 1988. 

Solar energy conversion and photovoltaic devices encompass one of the most active applied topics of research in this area191. Thus, photoelectrochemical cells based on electrodes (Sn02, Pt) coated with tetrapyrroles have been studied for a long time191-194. Most studies were performed with phthalocyanines due to their stability and wide range of redox... 

Solar energy conversion in photoelectrochemical cells with semiconductor electrodes is considered in detail in the reviews by Gerischer (1975, 1979), Nozik (1978), Heller and Miller (1980), Wrighton (1979), Bard (1980), and Pleskov (1981) and will not be discussed. The present chapter deals with the main principles of the theory of photoelectrochemical processes at semiconductor electrodes and discusses the most important experimental results concerning various aspects of photoelectrochemistry of a semiconductor-electrolyte interface a more comprehensive consideration of these problems can be found in the book by the authors (Pleskov and Gurevich,... 

The stability of semiconductor electrodes, their resistance to photocorrosion, become an especially urgent problem in connection with ever-extending photoelectrochemical applications of semiconductors. This refers, first of all, to electrodes of photoelectrochemical cells for solar energy conversion. 

The heterojunctions of the polyacetylene were realized not only with inorganic photoconductors but also with organic polymers [139]. The results obtained show good similarity with barrier and heterojunction characteristics for inorganic semiconductors. Photoelectrochemical cell for solar energy conversion with polyacetylene electrodes and Na2S, electrolyte had an efficiency of 1 % at 2.4 eV [140], The complicated phenomena take place at the electrodeelectrolyte interface. 

This volume, based on the symposium Photoeffects at Semiconductor-Electrolyte Interfaces, consists of 25 invited and contributed papers. Although the emphasis of the symposium was on the more basic aspects of research in photoelectrochemistry, the covered topics included applied research on photoelectrochemical cells. This is natural since it is clear that the driving force for the intense current interest and activity in photoelectrochemistry is the potential development of photoelectrochemical cells for solar energy conversion. These versatile cells can be designed either to produce electricity (electrochemical photovoltaic cells) or to produce fuels and chemicals (photoelectrosynthetic cells). 

The sensitization of electrodes to visible light by dye molecules is an old area of science with a rich history [2]. A dye-sensitized photoefifect was measured at a semiconductor surface as early as 1887 in Vienna [3]. The accepted mechanisms for the dye sensitization of electrodes emerged from photoelectrochemical studies in the 1960s and 1970s [4-6]. These studies were motivated by a desire to quantify interfacial electron transfer processes and develop cells useful for solar energy conversion. The two most common approaches are shown schematically in Figure 1. 

Semiconductor electrochemistry has various important applications, such as solar energy conversion by photoelectrochemical cells, photo-detoxification of organic waste, etching processes in semiconductor technology and device fabrication, photoplating and photography. In particular, the first-mentioned application provided a great impetus to research in the field of semiconductor electrochemistry. 

Such protecting systems are oxidized or reduced, thereby stabilizing semiconductor photoelectrodes, and this effect is used in photoelectrochemical cells for solar energy conversion. The solvent (e.g., water) can also act as a protector if it is oxidized (reduced) easier than the semiconductor electrode material. Situations like this arise with many oxide electrodes (Ti02, SrTi03,... 

Hall continues to put the case for large-scale biological solar energy conversion, but isolated systems have also received considerable attention in the laboratory. Bhardwaj et al have described a chloroplast photoelectrochemical cell in which chloroplasts were placed between an electron acceptor, such as anthraquinone-2-sulphonate and an electron donor, dichlorophenol or indo-phenol. The authors claim a 1% monochromatic power conversion efficiency for their most successful cells. Adams et by contrast, have used isolated... 

Generation of photocurrent at the semiconductor/electrolyte interface upon its illumination makes it possible to carry out photoelectrochemical reactions which can be used either for chemical fuel production, or purification of waters. Principles of operation of electrochemical cells with semiconductor electrodes for solar energy conversion to electrical and chemical energy are formulated. Most efficient cells for electricity and hydrogen production are surveyed. Certain processes for photo-destruction of pollutants, recovery of metals, etc. with making use of semiconductor dispersions are briefly discussed. 

These conditions are valid for any photoelectrochemical reaction, both for "useful" reactions that underlie the solar energy conversion in the PEC cells, and the deleterious reactions like (photo)corrosion reaction. Indeed, the latter reaction can be also assigned certain value of a reversible electrode potential, (p° (or electrochemical potential, Fjec). Hence, anodic decomposition of a semiconductor, with participation of holes is possible (in the dark) when... 

The optimization of photoelectrochemical devices for solar energy conversion depends on the choice of semiconductor, electrolyte, and cell design. The performance of the cell is strongly dependent upon the design, surface area, and placement of the counterelectrode and current collectors. This type of solar cell may be economical under concentrated illumination or in regions where electrical power has high value. 

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