PHOTOELECTROCHEMICAL CHARACTERIZATION

Renewed interest in semiconductor-liquid junctions started to emerge after it was demonstrated that a device based on partially reduced TiOj in contact with an aqueous electrolyte can sensitize photoelectrolysis of water (8). Immediatelyfollowing that work, the need tofind alternativefuel sources rekindled interest in solar energy. As a result, the study of energy conversion at semiconductor-liquid junctions grew to form almost a separate discipline that was named photoelectrochemistry,  

Before liquid-junctions can enter in force as an alternative junction technique to MOS and Schottky barriers for the characterization of semiconductors, a careful delineation of parameters thatareindependent of the nature of the junction will have to be compiled. To accomplish this, more fundamental work has to be done in comparative studies of the potential distribution under different junction configurations (9). 

Photoelectrochemistry is still an emerging discipline in that it is not yet possible to write this chapter in the form of a tutorial in which one can give a series of steps and techniques that, once applied to a given system, results in a complete understanding of the system in terms of structure, mechanism and kinetics. There is no single semiconductor/electrolyte system of which our understanding is sufficient for its predictive power to provide any degree of satisfaction. Afew systems such as Si and InP come close. 

Per definition, semiconductor/liquid junctions act as a focal pointfor 

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The redox behavior of the SeSO -Zn-EDTA system has been discussed on the basis of Pourbaix and solubility diagrams [11], Different complexes and substrates have been employed in order to optimize the electrodeposited thin films. By the selenosulfate method it is generally possible to grow ZnSe with an almost stoichiometric composition however, issues of low faradaic efficiency as well as crystallinity and compactiveness of the product, remain to be solved. Interestingly, in most reports of photoelectrochemically characterized ZnSe electrodeposits, the semiconductor film was found to be p-type under all preparation conditions (ZnSe is normally n-type unless deliberately doped p-type). 

Bhattacharya RN, Cahen D, Hodes G (1984) Electrodeposition of Cu-In-S layers and their photoelectrochemical characterization. Sol Energy Mater 10 41-45... 

Gutierrez MT, Salvador P (1987) Photoelectrochemical characterization and optimization of a liquid-junction photovoltaic cell based on electrodeposited CdSe thin films Influence of anneaUng and photoetching on the physical parameters determining the cell performance. Sol Energy Mater 15 99-113... 

Singh K, Siivastava ML, Mishra SSD (2006) Electrochemical deposition and photoelectrochemical characterization of colloidal HgS containing CdSe composites. Sol Energy Mater Sol Cells 90 923-932... 

Herrero J, Ortega J (1988) n-Type ln2S3 thin films prepared by gas chalcogenization of metalhc electroplated indium Photoelectrochemical characterization. Sol Energy Mater 17 357-368... 

Jaramillo TE, Baeck SH, Shwarsctein AK, Choi KS, Stucky GD, McFarland EW (2005) Automatated electrochemical synthesis and photoelectrochemical characterization of Zni-xCOxO thin film for solar hydrogen production. J Comb Chem 7 264-271... 

Miyake M, Torimoto T, Sakata T, Mori H, Yoneyama H (1999) Photoelectrochemical characterization of nearly monodispersed CdS nanoparticles-immobilized gold electrode. Langmuir 15 1503-1507 Torimoto T, Tsumura N, Miyake M, Nishizawa M, Sakata T, Moii H, Yoneyama H (1999) Preparation and photoelectrochemical properties two dimensionally organized CdS nanoparticle thin films. Langmuir 15 1853-1858... 

Mathew X, Bansal A, Turner JA, Dhere R, Mathews NR, Sebastian PJ (2002) Photoelectrochemical characterization of surface modified CdTe for hydrogen production. J New Mater Electrochem Systems 5 149-157... 

Valderrama RC, Sebastian PJ, Enriquez JP, Gamboa SA (2005) Photoelectrochemical characterization of GIGS thin films for hydrogen production. Sol Energy Mat Sol Cells 88 145-155... 

Photoelectrochemical characterization was also carried out on CdS films using different sizes of CdS nanocrystals [75]. Voe increased with decreasing crystal size from 0.58V (75 nm) to 0.68 V (5 nm). Surprisingly, he was not dependent... 

Besides evaluating photoelectrodes for use in PECs, photoelectrochemical characterization can be used for other purposes. For example, photocurrent spectra of CD CdS has been used to measure the semiconductor bandgap (as f vs. hv), and agreement between the bandgap values measured by this method and by absorption spectroscopy for as-deposited and annealed films was found [78]. 

The assembly of solar cells based on copper complexes required 2 optimization and multilayered photoanodes with a compact 2 underlayer, necessary to suppress the back recombination from the exposed FTO contact. The photoelectrochemical characterization carried out with a 0.2 M Cu(I)/Cu(II) electrolyte (Cu(II) molar... 

In the remainder of this section we briefly overview fundamental concepts, vocabulary, photoelectrochemical characterization techniques and the dye-sensitization mechanisms developed for planar electrodes. We end the section with a short literature review of dye-sensitization studies. 

N.R., and Sebastion, P.J. Photoelectrochemical Characterization of Surface Modified CdTe for Hydrogen Production, submitted to International Journal on New Materials for Electrochemical Systems. 

Miyake, M., T. Torimoto, T. Sakata, H. Mori, and H. Yoneyama, Photoelectrochemical characterization of nearly monodisperse CdS nanoparticles-immobilized gold electrodes. Langmuir, 1999. 15 pp. 1503-1507... 

Armstrong, N.R., Nebesny, K.W., Collins, G.E., Lee, P.A., Chau, L.K., Arbour, C., and Parkinson, B.A. (1991) 0/I-MBE formation of highly ordered phthalocyanine/semiconductor junctions by molecular-beam epitaxy photoelectrochemical characterization. Proc. SPIE, 1559,18-26. 

Yoshida, T., Oekermann, T., Okabe, K., Schlettwein, D., FunabiM, K., and Minoura, H. (2002) Cathodic electrodeposition of ZnO/eosinY hybrid thin films from dye added zinc nitrate bath and their photoelectrochemical characterizations. Electrochemistry, 70, 470d87. 

Idowu, M., Loewenstein, T., Hastall, A., Nyokong, T., and Schlettwein, D. (2010) Photoelectrochemical characterization of electrodeposited ZnO thin... 

Liang Y, Enache CS, Krol R (2008) Photoelectrochemical characterization of sprayed a-Fe203 thin films influence of Si doping and Sn02 interfacial layer. Int J Photoenergy 739864 1-7... 

P. Bertoncello, A. Natargiacomo, V. Erokhin, and C. Nicolini, Functionalization and photoelectrochemical characterization of poly[3-3 (vinylcarbazole)] multi-walled carbon nanotube (PVK-MWNT) Langmuir-Schaefer films. Nanotechnology, 17, 699-705 (2006). 

N.S. Gaikwad, G. Waldner, A. Bruger, A. Belaidi, S.M. Chaqour, M. Neumann-Spallait, Photoelectrochemical characterization of semitransparent WO3 films. J. Electrochem. Soc. 152, G411-G416 (2005)... 

T.F. Jaramillo, S.H. Baeck, A. Kleiman-Shwarsctein, K.S. Choi, G.D. Stucky, E.W. McFarland, Automated electrochemical synthesis and photoelectrochemical characterization of Zni xCoxO thin films for solar hydrogen production. J. Comb. Chem. 7, 264—271 (2005)... 

To determine the conductivity type, note the direction of potential shift with illumination. If OCP moves Positive (towards more anodic potentials) with illumination, the material is p-type. If OCP moves Negative (towards more cathodic potentials), the material is n-type. If the potential did not change with illumination, there may be an issue with electrode fabrication/contacts, the material may be photo-inactive under these conditions, or the material may not be viable for PEC applications. If no response to illumination is observed, it is doubtfiil that the material, as mounted, wiU respond to any other photoelectrochemical characterization techniques. However, the researcher may still wish to perform CV scans as described in section Three-Electrode j-V and Photocurrent Onset to completely rule out photoactivity of the material. 

T.G. Deutsch, J.L. Head, J.A. Turner, Photoelectrochemical characterization and durability analysis of GaInPN epilayers. J. Electrochem. Soc. 155, B903-B907 (2008)... 

Photoelectrodes, consisting of CdS nanocrystals that are directly attached to an electrode (gold or conducting oxide) or indirectly via a dithiol molecular linker have been studied extensively [19, 20, 116-120]. Here, we will focus on work that demonstrates the power of small-amplitude methods in photoelectrochemical characterization [26, 123, 124]. By measuring the photoelectrochemical activity of gold/Q-CdS electrodes, as the potential of the gold electrode was varied, it could be concluded that photoinduced electron transfer between the gold surface... 

The measurement of changes in the optical properties of nanocrystals attached to an electrode caused by variations in the electrode potential forms a challenging but interesting characterization method. Recently, a bleaching of the HOMO-LUMO transition of CdS nanocrystals has been observed when the electrode Fermi level was in resonance with the LUMO [128]. This led the authors to conclude that the pho-toexcited state in CdS contains an electron in the LUMO (and a trapped hole). This is in agreement with the results obtained by photoelectrochemical characterization of gold/Q-CdS electrodes (see earlier). 

Basu, J. and K.K. Rohatgi-Mukheijee (1991). Photoelectrochemical characterization of porphyrin-coated electrodes. Solar Energ. Mater. 21, 317-325. 

Yang, M.Z., M.G. de Backer, and F.X. Sauvage (1990). Electrochemical and photoelectrochemical characterizations of electrodes covered by zinc tetra 2,3 p5uidino-porphyrazine layers. New J. Chem. 14, 273-277. 

Fig. 4.9 Photoelectrochemical characterization of Si-doped Fc203 electrodes prepared by the APCVD technique. The left graph shows the current-voltage characteristics in darkness and under simulated sunlight (100 mW/cm ) at a scan rate of 50 mV/s. (a) Unmodified Fe203 (b) the same electrode after cobalt treatment. The right graph shows the incident photon-to-current efficiency (IPCE) spectrum of the same electrode at different conditions, (a) Unmodified Fc203 at 1.23 Yrhe (b) after cobalt deposition, at 1.23 Vrhe> (c) at 1.43 Vrhe, (d) at 1.03 Vrhe, (e) at 1.23 Vrhe but illuminated through the Sn02 substrate (f) absorption spectrum of this electrode. From [105] used with permission...

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