Liquid-junction solar cell

Following the same procedure, the kinetic constants have been determined for very different electrochemical conditions. When n-WSe2 electrodes are compared in contact with different redox systems it is, for example, found9 that no PMC peak is measured in the presence of 0.1 M KI, but a clear peak occurs in presence of 0.1 M K4[Fe(CN)6], which is known to be a less efficient electron donor for this electrode in liquid junction solar cells. When K4[Fe(CN)6] is replaced by K3[Fe(CN)6], its oxidized form, a large shoulder is found, indicating that minority carriers cannot react efficiently at the semiconductor/electrolyte junction (Fig. 31). 

Miller B, Heller A (1976) Semiconductor liquid junction solar cells based on anodic sulphide films. Nature 262 680-681... 

Tomkiewicz M, Ling I, Parsons WS (1982) Morphology, properties, and performance of electrodeposited n-CdSe in liquid junction solar cells. J Electrochem Soc 129 2016-2022... 

In any case, it is perceived from the above discussion that the problem of longterm chemical stability of polycrystalline semiconductor liquid junction solar cells is far from being solved. Still, as already pointed out in the early research, any practical photovoltaic and PEC device would have to be based on polycrystalline photoelectrodes. Novel approaches mostly involving specially designed PEC systems with alternative solid or gel electrolytes and, most importantly, hybrid/sensitized electrodes with properties dictated by nanophase structuring - to be discussed at the end of this chapter - promise new advances in the field. 

Heller A, Chang KC, Miller B (1977) Spectral response and efficiency relations in semiconductor liquid junction solar cells. J Electrochem Soc 124 697-700 Elhs AB, Kaiser SW, Wrighton MS (1976) Optical to electrical energy conversion. Characterization of cadmium sulfide and cadmium selenide based photoelectrochemical cells. J Am Chem Soc 98 6855-6866... 

McCann JF, Kainthla RC, Skyllas-Kazacos M (1983) Chemical deposition of Cdi xHgxS thin film electrodes for liquid-junction solar cells. Sol Energy Mater Sol CeUs 9 247-251... 

Robbins M, Bachmann KJ, Lambrecht VG, Thiel EA, Thomson J Jr., Vadimsky RG, Menezcs S, Heller A, Miller B (1978) CulnS2 liquid junction solar cells. J Electrochem Soc 125 831-832... 

Benniston AC, Haniman A (2008) Artificial photosynthesis. Materials Today 11 26-34 Inoue T, Fujishima A, Konishi S, Honda K (1979) Photoelectrocatalytic reduction of carbon dioxide in aqueous suspensions of semiconductor powders. Nature 277 637-638 Halmann M (1978) Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells. Nature 275 115-116 Heminger JC, Carr R, Somorjai GA (1987) The photoassisted reaction of gaseous water and carbon dioxide adsorbed on the SrH03 (111) crystal face to form methane. Chem Phys Lett 57 100-104... 

M. Halmann. Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells. Nature. 1978, 275(5676) 115-116. 

Water is involved in most of the photodecomposition reactions. Hence, nonaqueous electrolytes such as methanol, ethanol, N,N-d i methyl forma mide, acetonitrile, propylene carbonate, ethylene glycol, tetrahydrofuran, nitromethane, benzonitrile, and molten salts such as A1C13-butyl pyridium chloride are chosen. The efficiency of early cells prepared with nonaqueous solvents such as methanol and acetonitrile were low because of the high resistivity of the electrolyte, limited solubility of the redox species, and poor bulk and surface properties of the semiconductor. Recently, reasonably efficient and fairly stable cells have been prepared with nonaqueous electrolytes with a proper design of the electrolyte redox couple and by careful control of the material and surface properties [7], Results with single-crystal semiconductor electrodes can be obtained from table 2 in Ref. 15. Unfortunately, the efficiencies and stabilities achieved cannot justify the use of singlecrystal materials. Table 2 in Ref. 15 summarizes the results of liquid junction solar cells prepared with polycrystalline and thin-film semiconductors [15]. As can be seen the efficiencies are fair. Thin films provide several advantages over bulk materials. Despite these possibilities, the actual efficiencies of solid-state polycrystalline thin-film PV solar cells exceed those obtained with electrochemical PV cells [22,23]. 

Parkinson, B.A., Heller, A., and Miller, B., Effects of cations on the performance of the photoanode in the n-gallium arsenide/potassium selenide (K2Se)-potassium diselenide (K2Se2)-potassium hydroxide/carbon semiconductor liquid junction solar cell, /. Electrochem. Soc., 126,954,1979. 

Bhattacharya, R. N. Pramanik, P. 1982. Semiconductor liquid junction solar cell based on chemically deposited Bi2S3 thin film and some semiconducting properties of bismuth chalcogenides. J. Electrochem. Soc. 129 332-335. 

As described in Section 3 of Chapter 4, the stabilization of n-Si electrode by coating with poly(pyrrole) has attracted much attention. The stabilization of a small bandgap n-semiconductor electrode against oxidation is of great value not only to convert visible light into chemical energy, but also to construct liquid-junction solar cells operated under visible irradiation. The poly(pyrrole) film is usually electropolymerized on the semiconductor electrode dipped in the aqueous solution of pyrrole. The remarkable stabilizing effect of poly(pyrrole) film on polycrystalline n-Si is shown in Fig. 22 67). The photocurrent obtained under irradiation in the aqueous solution of... 

In summary, at nanostructured tin-oxide semiconductor-aqueous solution interfaces, back ET to molecular dyes is well described by conventional Marcus-type electron-transfer theory. The mechanistic details of the reaction, however, are remarkably sensitive to the nature of the semiconductor-dye binding interactions. The mechanistic differences point, potentially, to differing design strategies for kinetic optimization of the corresponding liquid-junction solar cells. 

Ions that are not chemisorbed do not affect the performance of semiconductor liquid junction solar cells.32 Weakly chemisorbed ions produce inadequate splitting of surface states between the edges of the conduction and valence band and increase rather than decrease the density of the surface states in the band gap and thus the recombination velocity. Bi3+ is an example of such an ion. As seen in Figure 5, it decreases the efficiency of the n—GaAs 0.8M K2Se-0.1M K2Se2-lM KOH c cell.30 Since the chemisorption of Bi3+ is weak, the deterioration in performance is temporary. The ion is desorbed in 10 min. and the cell recovers. 

Inoue, T., Watanabe, T., Fujishima, A., and Honda, K., Competitive Oxidation at Semiconductor Photoanodes, in Semiconductor Liquid--Junction Solar Cells, Heller, A., Ed., The Electrochemical Society, Princeton, N3, 1977, 210. 

Heller, A., ed. "Semiconductor Liquid Junction Solar Cells" The Electrochemical Society, Inc. Princeton, N.J., 1977. 

When CdSe was in contact with the solid electrolyte containing iodine redox species, negative photopotentials and anodic photocurrents were detected. This is analogous to the behavior of n--type semiconductor in liquid-junction solar cells. In the case of solid... 

J. F. Gibbons, G. W. Cogan, C. M. Gronet, and N. S. Lewis, A 14% efficient nonaqueous semicon-ductor/liquid junction solar cell, Appl Phys. Lett. 45(10), 1095, 1984. 

C. M. Gronet, N. S. Lewis, G. Cogan, and J. Gibbons, n-type silicon photoelectrochemistry in methanol Design of a 10.1% efficient semiconductor/liquid junction solar cell, Proc. Natl. Acad. Sci. USA 80, 1152, 1983. 

We are investigating the effects of binding non-electroactive molecules to electrode surfaces. The attached layer will be sufficiently thin (ca. 1 monolayer) that electron transfer across the electrode/electrolyte interface will not be inhibited. However, other surface properties may be advantageously modified. For semiconductor electrodes, desirable changes include suppression of the photo-activated surface corrosion and shifts in the flatband potential. We are seeking to improve the performance of semiconductor liquid-junction solar cells by these means. 

Gibbons J. F., Cogan G. W., Gronet C. M. and Lewis N. S. (1984), A 14% efficient nonaqneons semicondnctor liquid junction solar cell , Appl. Phys. Lett. 45, 1095-1097. 

Tenne R. and Hodes G. (1980), Improved efficiency of cadmium selenide photoanodes by photoelectrochemical etching , Appl. Phys. Lett. 37, 428-430. Tomkiewicz M., Ling 1., and Parsons W. S. (1982), Morphology, properties, and performance of electrodeposited normal CdSe in liquid-junction solar cells ,... 

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