Photoelectrochemical solar cell

In practice, the electrochemical behavior of semiconductor-electrolyte interfaces is far more complex than that described above (for a good review, see Boddy [1965]). One of the complications arises because the semiconductor surface at the electrolyte-semiconductor interface is not equivalent to that in the bulk. In particular, the energy states localized at the surface for holes and/or electrons are different than those present in the bulk. These surface states may arise in several ways—for example through pretreatment (etching, polishing, etc.) of the semiconductor surface before immersion in the electrolyte. The surface states can be detrimental to the PESC efhciency if they increase the recombination of the electron-hole pairs in the semiconductor, thus reducing the number of holes (electrons for p-type material) available for chemical reaction with the redox species in solution. 

Another complication arises because the semiconductor may chemically or electrochemically react with the electrolyte after immersion, leaving a layer on the surface of the semiconductor which has different electrical or electrochemical characteristics (e.g. an insulating layer) from the semiconductor. Because the photocurrent under illumination is very sensitive to the semiconductor-electrolyte interface, these surface perturbations not only ehange the electrochemical behavior but they can, in extreme cases, completely inhibit the photoresponse. 

In the case of the polished + etched + oxidized sample, C was associated with the space charge layer capacitance. No further data were used. Thus, Ci is representative of the change in capacitance of the space charge layer from the presence of the oxide layer. 

To determine the effect of oxidation, a Mott-Schottky plot of the space charge capacitance before and after oxidation was compared. In these plots, which were originally derived for a metal-semiconductor interface (Schottky [ 1939,1942], Mott [1939]) but hold equally well for the metal-electrolyte interface, a linear relationship is predicted between the applied potential and one over the square of the capacitance arising from the space charge layer in the saniconductor. The slope is inversely proportional to the effective donor or acceptor concentration in the semiconductor. For the semiconductor-electrolyte interface (Bard and Faulkner [1980]), 

Several key features of this study should be emphasized. IS clearly can be used to successfully model a semiconductor-electrolyte interface in a PESC. The ability to probe the physics of this interface using IS while controlling the applied potential can allow significant insight into the important parameters of the device. In particular, the surface states at the semiconductor-electrolyte interface may be determined, as can their relative importance after several different pretreatments or in different cell configurations. The electrical characteristics of the interface, for example the flat-band potential and the space charge capacitance, can also be determined. 

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Aqueous polysulflde solutions have been widely investigated as primary electrolytes in photoelectrochemical solar cells (PEC Chap. 5). The complexity of these solutions arising from the overlap of multiple chemical equilibria is well... 

Licht S (1995) Electrolyte modified photoelectrochemical solar cells. Sol Energy Mater Sol Cells 38 305-319... 

Erese KW Jr (1982) A high efficiency single-crystal CdSe photoelectrochemical solar cell and an associated loss mechanism. Appl Phys Lett 40 275-277... 

Licht S, Peramunage D (1990) Efficient photoelectrochemical solar cells from electrolyte modification. Nature 345 330-333... 

Hodes G, Manassen J, Neagu S, Cahen D, Mirovski Y (1982) Electroplated cadmium chalcogenide layers Characterization and use in photoelectrochemical solar cells. Thin Solid Films 90 433-438... 

Mirovsky Y, Tenne R, Hodes G, Cahen D (1982) Photoelectrochemical solar cells Interpretation of cell performance using electrochemical determination of photoelectrode properties. Thin Solid Films 91 349-355... 

Bhattacharya RN (1986) Electrodeposited CdSeo.sTeo.s photoelectrochemical solar cells. J Appl Electrochem 16 168-174... 

Licht S (1986) Combined solution effects yield stable thin-film Cd(Se,Te)/polysulfide photoelectrochemical solar cells. J Phys Chem 90 1096-1099... 

Mirovsky Y, Cahen D (1982) n-CulnSe2/fK)lysulfide photoelectrochemical solar cells. Appl Phys Lett 40 727-728... 

Pandey RN, Misra M, Srivastava ON (1998) Solar hydrogen production using semiconductor septum (n-CdSe/n and n-U02/Ti) electrode based photoelectrochemical solar cells. Int J Hydrogen Energy 23 861-865... 

Nakato K, Takabayashi S, Imanishi A, Murakoshi K, Nakato Y (2004) Stabilization of n-Si electrodes by surface alkylation and metal nano-dot coating for use in efficient photoelectrochemical solar cells. Sol Energy Mater Sol Cells 83 323-330... 

Narayanan, R., M. Deepa, and A.K. Srivastava, Nanoscale connectivity in a Ti02/CdSe quantum dots/functionalized graphene oxide nanosheets/Au nanoparticles composite for enhanced photoelectrochemical solar cell performance. Physical Chemistry Chemical Physics, 2012.14(2) p. 767-778. 

Kongkanand, A. Martinez Dominguez, R. Kamat, P. V., Single wall carbon nanotube scaffolds for photoelectrochemical solar cells. Capture and transport of photogenerated electrons. Nano Lett. 2007, 7, 676-680. 

Rh2 is the rate of production (moles/s) of hydrogen in its standard state per unit area of the photoelectrode. The standard Gibbs energy AG° = 237.2 kj/mol at 25°C and 1 bar, and Pt is the power density (W/m ) of illumination. The numerator and denominator have units of power and hence, as in the case of photoelectrochemical solar cells, the photoconversion efficiency is the ratio of power output to the power input. 

Aqueous polysulfide electrolytes are regularly the matter of fundamental photo-electrochemical studies (see Sect. 5.2 in Volume 6) and of the development of high-energy efficiency and highly stable photoelectrochemical solar cells [100,101]. Aqueous polysulfide solution chemistry is also of importance to the pulp and paper industry [102], and provides an opportunity for a battery cathode based on the... 

Figure 2 A module of an photoelectrochemical solar cell based on a dye-sensitized TiOz nanocrystalline film.

Study of the Potential Distribution at the Semiconductor-Electrolyte Interface in Regenerative Photoelectrochemical Solar Cells... 

Over the past 15 years there has been a wealth of research on development and application of transition metal complex sensitizers to the development of dye sensitized photoelectrochemical (solar) cells (DSSCs) [113]. Charge injection from the excited state of many sensitizers has been found to be on the subpicosecond timescale, and a key objective has been to identify chromophores that absorb throughout the visible spectrum. For this reason, Os(II) complexes appear attractive and a variety of attempts were made to make use of these complexes in DSSCs in the 1990s [114-116]. Work has continued in this area in recent years and representative examples are given below. 

The electronic properties of semiconductors junctions are strongly dependent on their interfaces. This is especially true for semiconductor/electrolyte contacts as in photoelectrochemical solar cells, for which a variety of possible reactants must be considered. 

In this paper our results to simulate the photoactive semiconductor/ electrolyte interface in UHV by adsorbing halogens and H20 on semiconductor surfaces are described. For these experiments layer type compounds and ternary chalcogenides have been considered because clean faces can easily be prepared by cleaving the crystals in UHV and because the reactions with halogens are intensively studied for photoelectrochemical solar cells. 

For instance, in a photovoltaic or a photoelectrochemical solar cell, a (small) drop in the electrochemical potential over the active phase is necessary for collecting the electrons [6, 9]. However, it leads to a decrease of the work that an electron can perform in the external circuit. 

Sorensen, B. (2002b). Understanding photoelectrochemical solar cells. In "PV in Europe, from PV Technology to Energy Solutions", Roma Int. Conf. ( Bal, J., et al, eds.), pp. 3-8. WIP Munich and ETA Florence. 

A. Switzer, The n-silicon/thallium (111) oxide heterojunction photoelectrochemical solar cell, J. Electrochem. Soc. 133, 722, 1986. 

Y. Nakato, K. Ueda, and H. Tsubomura, Novel approch to efficient photoelectrochemical solar cells using electrolyte/discontinuous metal/semiconductorjunction, J. Pkys. Chem. 90, 2090, 1986. 

As will be shown in Section 2.4, these observations have a large impetus on the performance of photoelectrochemical solar cells. It should also be mentioned the reverse processes, here the oxidation of the redox system, does not necessarily also occur via the conduction band. Since the reorganisation energies are typically in the range of A, = 0.5-1.2 eV, the oxidation of the redox couple may occur via the valence band, especially for semiconductors of a bandgap smaller than 2 eV. 

Tachibana Y., Akiyama H. Y., Ohtsuka Y., Torimoto T. and Kuwabata S. (2007), CdS quantum dots sensitized Ti02 sandwich type photoelectrochemical solar cells , Chem. Lett. 36, 88-89. 

SEMICONDUCTOR/LIQUID JUNCTION PHOTOELECTROCHEMICAL SOLAR CELLS... 

Semiconductor/Liquid Junction Photoelectrochemical Solar Cells... 

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