Charge transport chemistry effects

Nieto, R, Jr., and Tucceri, R.L 1996. The effect of pH on the charge transport at redox polymer-modified electrodes An a.c. impedance smdy apphed to poly(o-aminophenol) film electrodes. Journal of Electroanalytical Chemistry 416, 1-24. 

In this chapter we report on properties of nanometer-sized semiconductor particles in solution and in thin films and thereby concentrate on the photochemical, photophysical, and photoelectrochemical behavior of these particles. We shall, very briefly, describe the energetic levels in semiconductors and the size quantization effect. The bottleneck in small-particle research is the preparation of well-defined samples. As many preparative aspects are already reviewed in several actual assays, we present here only the preparative highlights of the last two years. In Section IV we describe the fluorescence properties of the particles. We report on different models for the description of the very complex fluorescence mechanism and we show how fluorescence can be utilized as a tool to learn about surface chemistry. Moreover, we present complex nanostructures consisting of either linked particles or multiple shells of different nanosized materials. The other large paragraph describes experiments with particles that are deposited on conductive substrates. We show how the combination of photoelectrochemistry and optical spectroscopy provides important information on the electronic levels as well as on charge transport properties in quantized particle films. We report on efficient charge separation processes in nanostructured films and discuss the results with respect to possible applications as new materials for optoelectronics and photovoltaics. 

This phenomenon is akin to thermodynamic phase transitions in other branches of physical chemistry. The abrapt deterioration of the charge transport rate in poly(tetracyanoquinodimethane Fig. 6.22) or poly(vinylferrocene) films [23] at high electrolyte concentrations (10moldm LiCl or 5moldm CaCh) and its temperature dependence (Fig. 6.23) can be interpreted based on thermodynamic theory [20,23,222]. In a more compact stracture the rate of electron hopping may increase since the concentration of redox sites is high however, a deterioration in the film s permeability to the counterions due to the decrease in the free volume is expected at the same time. The maximum observed in the peak current versus salt concentration curve is the result of the balanced effects of the enhanced electron-... 

In Chap. 9 Alessandro Troisi blocks out disorder effects by focusing on the charge transport in crystalline organic media. In this way, the interplay between a compound s electrical characteristics and the chemical structure of the soft lattice dressing of the effective masses and energies by local distortions can be examined from a microscopic point of view by the means of computational chemistry. 

Kubo, W. Murakoshi, K Kitamura, T. Yoshida, S. Haruki, M. Hanabusa, K. Shirai, H. Wada, Y. Yanagida, S. (2001). Quasi-solid-state dye-sensitized TiQz solar cells effective charge transport in mesoporous space filled with gel electrolytes containing iodide and iodine. Journal of Physical Chemistry B, 105, 2001, 12809-12815. 

Using a stable dopant as the emissive dye has been shown to greatly enhance the lifetime of small molecule LEDs. Rubrene doped into the Alq, electron transport layer ] 184] or into the TPD hole transport layer 1185] can extend the lifetime by an order of magnitude. Similarly, dimclhylquinacridone in Alq has a beneficial effect ]45 ]. The likely mechanism responsible for this phenomenon is that the dopant acts as a trap for the excilon and/or the charge. Thus, molecules of the host maLrix are in their excited (cationic, anionic or cxcitonic) states for a smaller fraction of the time, and therefore have lower probability to undergo chemistry. 

The above classification of chemical processes was based on the system s physical chemistry. A similar classification can be applied to electronic processes if we consider the effectively charged structure elements and assume that we can determine extremely small component concentrations or deviations from the stoichiometric composition. The well-known p-n junction process can serve as an example since it is a transport process (including local relaxation) in a single phase, inhomogeneous system. 

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