Interface under illumination

DCE interface in the presence of TPBCl [43,82]. The accumulation of products of the redox reactions were followed by spectrophotometry in situ, and quantitative relationships were obtained between the accumulation of products and the charge transfer across the interface. These results confirmed the higher stability of this anion in comparison to TPB . It was also reported that the redox potential of TPBCP is 0.51V more positive than (see Fig. 3). However, the redox stability of the chlorinated derivative of tetra-phenylborate is not sufficient in the presence of highly reactive species such as photoex-cited water-soluble porphyrins. Fermin et al. have shown that TPBCP can be oxidized by adsorbed zinc tetrakis-(carboxyphenyl)porphyrin at the water-DCE interface under illumination [50]. Under these conditions, the fully fluorinated derivative TPFB has proved to be extremely stable and consequently ideal for photoinduced ET studies [49,83]. Another anion which exhibits high redox stability is PFg- however, its solubility in the water phase restricts the positive end of the ideally polarizable window to < —0.2V [85]. 

Salvador [100] introduced a non-equilibrium thermodynamic approach taking entropy into account, which is not present in the conventional Gerischer model, formulating a dependence between the charge transfer mechanism at a semiconductor-electrolyte interface under illumination and the physical properties thermodynamically defining the irreversible photoelectrochemical system properties. The force of the resulting photoelectrochemical reactions are described in terms of photocurrent intensity, photoelectochemical activity, and interfacial charge transfer... 

Fig. 16.4 Charge transfer at the n-type semiconductor-solution interface under illumination [Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission from Memming (2001)]...

FIGURE 1.19. Creation and movement of electronic carriers at the semiconductor/electrolyte interface under illumination. 

K. Chandrasekaran, R. C. Kainthla, and J. O. Bockris, An impedance study of the silicon-solution interface under illumination, Electrochim. Acta 33, 327, 1988. 

The surface states at the semiconductor electrolyte interface under illumination for the electrochemical redjgtion of carbon dioxide has been determined to be 10 cm. Surface states are induced by adsorbed ions and act as faradaic mediators for the photo-electrochemical reduction of carbon dioxide. It is shown that CO is adsorbed on platinum and adsorbed C0 is the intermediate radical. The rate determining step involves further reduction of CO to give the final products. Adsorption of NH, ions on p-GaP has been studied using FTIRRAS. At cathodic potentials adsorbed ammonium ions are reduced and the reduced ammonium radical desorbs. The structure of adsorbed ammonium is investigated. 

Figure 20 is a schematic representation of a p-type semiconductor/electrolyte interface under illumination. Each absorbed photon, the energy of which is larger than the energy gap of the semiconductor, makes an excited electron in the conduction band and a hole in the valence band. Some of the excited electrons reach the semiconductor surface and some recombine with holes before reaching the surface. The electrons which reach the surface would transfer to an acceptor (oxidized form of a redox couple), be trapped by surface states, or recombine with holes in the valence band at the... 

Figure 20. Schematic representation of p-type semiconductor/electrolyte interface under illumination. Semiconductor side is divided into space charge region (SCR) and field free region (FFR) at x = W. Numbers in the figure represent the following steps (1) Excitation of an electron from the valence band to the conduction band, leaving a hole in the valence band. (2) Recombination in the bulk. (3) Recombination in the space charge region. (4) Electron transfer from the conduction band to an oxidized state. (5) Electron capture by a surface state. (6) Electron transfer from the surface state to the oxidized state (electron transfer via surface state). (7) Hole capture by the surface state (surface recombination via surface state). There is also a possibility of direct recombination of a conduction band electron with a valence band hole, although this step is not shown in the figure.

In the first chapter, Uosaki and Kita review various theoretical models that have been presented to describe the phenomena that occur at an electrolyte/semiconductor interface under illumination. In the second chapter, Orazem and Newman discuss the same phenomena from a different point of view. In Chapter 3, Boguslavsky presents state-of-the-art considerations of transmembrane potentials and other aspects of active transport in biological systems. Next, Burke and Lyons present a survey of both the theoretical and the experimental work that has been done on hydrous oxide films on several metals. 

The multiple band gap solar to electrical conversion efficiency of 19.2% compares favorably to the maximum 15 to 16% solar to electrical energy conversion efficiency previously reported for single band gap PECs [9, 10]. Small photoelectrochemical efficiency losses can be attributed to polarization losses accumulating at the solution interfaces. Under illumination, a photocurrent density of 13 mA cm seen in Fig. 7 is consistent with polarization... 

Physics of Semiconductor-Liquid Interfaces Under Illumination (A. Heller, Ed.), Princeton Electrochemical Society (1977). 

The flux of charge carriers across the semiconductor/electrolyte interface under illumination is dependent on the potential (E), the electron density (n), and the hole density (p) throughout the semiconductor. The calculation of electron and hole current flow requires the use of the Poisson, steady-state carrier continuity equations and carrier transport equations ... 

---