Electrochemical solar cell

An interesting idea has been to prepare the photosensitive electrode on site having the liquid play the dual role of a medium for anodic film growth on a metal electrode and a potential-determining redox electrolyte in the electrochemical solar cell. Such integration of the preparation process with PEC realization was demonstrated initially by Miller and Heller [86], who showed that photosensitive sulfide layers could be grown on bismuth and cadmium electrodes in solutions of sodium polysulfide and then used in situ as photoanodes driving the... 

Gerischer H, Gobrecht J (1976) On the power characteristics of electrochemical solar cells. Ber Bunsenges Phys Chem 80 327-333... 

Gobrecht J, Tributsch H, Gerischer H (1978) Performance of synthetical n-MoSc2 in electrochemical solar cells. J Electrochem Soc 125 2085-2086... 

As it has been described in various other review articles before, the conversion efficiencies of photovoltaic cells depend on the band gap of the semiconductor used in these systems The maximum efficiency is expected for a bandgap around Eg = 1.3eV. Theoretically, efficiencies up to 30% seem to be possible . Experimental values of 20% as obtained with single crystal solid state devices have been reported " . Since the basic properties are identical for solid/solid junctions and for solid/liquid junctions the same conditions for high efficiencies are valid. Before discussing special problems of electrochemical solar cells the limiting factors in solid photovoltaic cells will be described first. 

Table 1. Photovoltage Up, photocurrent ip fill factor FF and efficiency p of regenerative electrochemical solar cells... 

The scale of electrochemical work functions makes it possible to calculate the outer potential difference between a solution and any electrode provided the respective reaction is in equilibrium. A knowledge of this difference is often important in the design of electrochemical systems, for example, for electrochemical solar cells. However, in most situations one needs only relative energies and potentials, and the conventional hydrogen scale suffices. 

Heller A (1982) Electrochemical solar cells. Solar energy 29 153-162... 

Figure 15.1 Schematic illustration of two types of photoelectrochemical cells. A dye-sensitized solar cell (left) a conventional electrochemical solar cell (right). (1) A dye-loaded porous wide gap semiconductor (2) transparent conducting grass, (3) an electrolyte containing a redox couple, (4) Pt or carbon counter electrode, (5) a sealing material, (6) back contact, (7) a semiconductor electrode (n-type). Photogeneration of electron has occurred at the gray zone.

Audas, R. and Irwin, J.C., Investigation of the Performance of an M0S2/17I2/C Electrochemical Solar Cell, J.Appl.Phys., 52, 6954, (1981). 

Fornarini, L., Stirpe, F., Scrosati, 8. and Razzini, G., Electrochemical Solar Cells with Layer-Type Semiconductor Anodes. Performance of n-MoSs Cells, Solar Energy Materials, 5, 107, (1981). 

L. Fomarini, F. Stirpe, and B. Scrosati, Electrochemical solar cells with layer-type semiconductor anodes. Nonaqueous electrolyte cells, J. Electrochem. Soc. 129, 1155, 1982. 

Figure 10.13 Energy diagram for a bipolar-bandgap indirect ohmic storage multiple-bandgap photo-electrochemical solar cell (MBPEC) (Licht et al, 1998 and 1999).

Heller A. (1982), Electrochemical solar cells , in lUPAC Frontiers of Chemistry, Laidler K. J (ed.), Pergamon, Oxford, New York, pp.27-40. 

Sharon M. (1988), Photoelectrochemical solar cells , in Santhanam K. S. V. and Sharon M. (eds.). Studies in Physical and Theoretical Chemistry, Vol. 50 Photo-electrochemical Solar Cells, Elsevier, New York, p. 162. 

The most important advantage of photoelectrochemical cells with semiconductor electrodes, as compared to, for example, solid-state semiconductor solar cells, is a relatively low sensitivity of their characteristics to the crystalline perfection of the semiconductor and the degree of its purification. Polycrystalline semiconductor electrodes in electrochemical solar cells exhibit both high absolute and high relative (as compared to single-crystal electrodes) conversion efficiency. This opens, at least in principle, the way of... 

Measurements with crystals of moderate photoelectrical quality non-specific reaction with holes specific photoreaction e.g. with C) photocurrents shift characteristically with redox potential photointercalation solar energy conversion and storage regenerative electrochemical solar cells photodecomposition of HI into jHj + photoelectroanalytical probe. 

Figure 29. Schematic illustration of a regenerative dye-sensitized electrochemical solar cell. CB, conduction band VB, valence band of the semiconductor D, dye molecule Red/Ox, redox couple electrolyte C, counterelectrode.

J. Gobrecht, R. Potter, R. Nottenburg, and S. Wagner, An n-CdSe/SnO2/n-Si tandem electrochemical solar cell, J. Electrochem. Soc. 130 (1983) 2280-2283. 

W. Kautek and H. Gerischer, A kinetic derivation of the photovoltage for electrochemical solar cells employing small-band gap semiconductors, Elec-trochim. Acta 27 (1982) 355-358. 

Indium phosphide has been a successful material in the preparation of solid-state, photovoltaic, and photoelectrocatalytic electrochemical solar cells [237-240]. Photovoltaic soUd-state solar cells reach single-junction efHciencies above 24% [237]. When used as a photocathode in photoelectrochemical solar energy conversion, the material has shown excellent stability [239], related to the unique surface chemistry of the polar InP(lll) A-face that exposes In atoms only [240]. The photoelectrochemical conditioning of single-crystalline p-type InP with the aim of preparing efficient and stable photoelectrochemical solar cells for photovoltaic and photoelectrocatalytic operation is described in the following and the induced surface transformations are analyzed employing a variety of surface-sensitive methods. 

For application in solid-state devices, the structure would be covered by a transparent conducting oxide (TCO) such as ZnO or indium tin oxide (ITO), followed by the contact finger system. For electrochemical solar cells, a redox electrolyte is used as contact In photovoltaic systems, typical redox couples such as Fe(II)/(III),... 

H., Lindquist, S.E, and Hagfeldt, A, (2002) A 5% effident photo electrochemical solar cell based on nanostructured ZnO electrodes. Solar Energy Mater. Solar Cells, 73, 51-58,... 

Polymer electrolytes have interesting properties for practical use in batteries, smart windows, and electrochemical solar cells, fuel cells, and water desalination [58], The electrolyte system lets the batteries to be produced in countless structures and has been used in devices as well as cellular telephones and laptop computers [18],... 

Esposito DV, Dobson KD, McCandless BE, Birkmire RW, Chen JG (2009) Comparative study of tungsten monocarbide and platinum as counter electrodes in polysulfide-based photo-electrochemical solar cells. J Electrochem Soc 156 B962-B969... 

Jackowska, K., and Tien, H. T., Electrochemical solar cells with polypyrrole coated CdBe sintered electrodes, J. Appl. Electrochem., 18, 357-362 (1988). 

In summarizing, one can say that the conversion efficiencies of electrochemical solar cells with semiconductor electrodes are very similar to those for solid state devices. Additional problems arise by the possibility that the electron transfer reactions at the interfaces can be slow. This disadvantage may however be compensated by the larger flexibility in the adjustment of the redox potentials of the electrolytes to the properties of the semiconductors and by the very simple formation of the heterojunction at which the unfavorable effects of interfacial electronic states are less pronounced. The most serious problem of such cells remains the photodecomposition which has to be overcome before such devices can reach practical importance. 

Schwarzburg K, Willig F (1999) Origin of photovoltage and photocurrent in the nanoporous dye-sensitized electrochemical solar cell. J Phys Chem B 28 5743-5746... 

---