Semiconductor polycrystalline

In any case, it is perceived from the above discussion that the problem of longterm chemical stability of polycrystalline semiconductor liquid junction solar cells is far from being solved. Still, as already pointed out in the early research, any practical photovoltaic and PEC device would have to be based on polycrystalline photoelectrodes. Novel approaches mostly involving specially designed PEC systems with alternative solid or gel electrolytes and, most importantly, hybrid/sensitized electrodes with properties dictated by nanophase structuring - to be discussed at the end of this chapter - promise new advances in the field. 

The effect of adsorption surface charging on electrophysical characteristics of polycrystalline semiconductor adsorbents... 

Above theoretical analysis of adsorption effects on electric conductivity and VAC profiles in polycrystalline semiconductor adsorbent with accounting for its barrier disorder indicate that the value and kinetics of change in o(t) and yS(t) during adsorption of both acceptors and donors sharply differ from those predicted by theory both for the case of ideal monocrystal and for polycrystal considered from the standpoint of bicrystal model. 

The percolation model of adsorption response outlined in this section is based on assumption of existence of a broad spread between heights of inter-crystalline energy barriers in polycrystals. This assumption is valid for numerous polycrystalline semiconductors [145, 146] and for oxides of various metals in particular. The latter are characterized by practically stoichiometric content of surface-adjacent layers. It will be shown in the next chapter that these are these oxides that are characterized by chemisorption-caused response in their electrophysical parameters mainly generated by adsorption charging of adsorbent surface [32, 52, 155]. The availability of broad spread in heights of inter-crystalline barriers in above polycrystallites was experimentally proved by various techniques. These are direct measurements of the drop of potentials on probe contacts during mapping microcrystal pattern [145] and the studies of the value of exponential factor of ohmic electric conductivity of the material which was L/l times lower than the expected one in case of identical... 

Thus, as it can be concluded from above, we obtained a satisfactory agreement between results predicted by the percolation model of adsorption response of electrophysical parameters of polycrystalline semiconductor adsorbent with experimental data. This clarified several cases which have not been recently satisfactorily explained. 

Thus, all above experimental examples indicate that additionally to effect of disordering of the surface of adsorbent on its adsorption characteristics it is necessary to account for the effect of the adsorption itself on degree of adsorbent disordering controlling both its own electrophysical characteristics and the adsorption-caused change while deriving the theory of adsorption response of polycrystalline semiconductor adsorbent. 

Above we have considered the possibility of existence of various types of polycrystalline semiconductor adsorbents differing in the character of contact of specific microcrystals. Let us consider the effect of this difference on adsorption and electrophysical properties of adsorbents in more detail and, which is more important, address the item of the mechanisms of the change of electrophysical properties of semiconductor caused by its interaction with gaseous phiise. 

Absolutely different situation occurs in case of polycrystalline semiconductors obtained under vacuum conditions. Thus, in paper [30] three types of ZnO samples were studied ZnO 1 obtained during heating of carbonates containing zinc in air at 600 C ZnO 2 obtained through vacuum decomposition of carbonate followed by heating at 500°C ZnO 3 powder of spectrally pure zinc oxide. 

For either conventional polycrystalline semiconductors or nanotubes and nanowires to be successful, the development of model and simulation tools that can be used for device and circuit design as well as for predictive engineering must be available. Since these devices are not necessarily based on single wires or single crystals, but rather on an ensemble of particles, the aggregate behavior must be considered. Initial efforts to provide the necessary physical understanding and device models using percolation theory have been reported.64,65... 

Based on our observations, we have reason to believe that single crystal performance will be approached in future thin film, polycrystalline semiconductor based solar cells with grain boundary recombination velocities reduced by strongly chemisorbed species. 

This process is obviously a natural scattering process in polycrystalline materials, since polycrystalline films exhibit a high concentration of crystallographic defects, especially dislocations [133,134]. However, this process is rarely used to explain experimental data of carrier transport in polycrystalline semiconductors and especially transparent conducting oxides [88], which is mainly due to the fact that in most works on transport properties of polycrystalline films the density of defects was not determined. Podor [135] investigated bended n-type Ge crystals with a dislocation density around 107 cm 2... 

J. Werner, in Polycrystalline Semiconductors Ill-Physics and Technology, ed. by H. Strunk, J. Werner, B. Fortin, O. Bonaud (Scitec Publ., Switzerland, Zug, Switzerland, 1993), p. 534... 

This chapter presents a quantitative method to determine the photoadsorption capacity of a polycrystalline semiconductor oxide irradiated in liquid-solid system. The determination is performed imder reaction conditions so that it is really indicative of the photoadsorption capacity. The method uses the experimental results obtained in typical batch photoreactivity runs on this ground it has been applied to the following photocatalytic processes carried out in aqueous suspensions (i) oxidation of phenol in the presence of a commercial Ti02 catalyst (Degussa P25) and... 

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... 

The electrical conductivity of the solid would also vary as a function, of the impurity nature and the chemical effect of these must be different. However, experimental results show that the relationship between conductivity and catalytic activity is much more complex. This is probably due to the fact that the conductivity of polycrystalline semiconductors often is not affected by changes in the Fermi level of the surface. Thus there must be another connection between changes in electron work functions of modified catalysts and their adsorptive and catalytic activities. 

G.Harbeke, Polycrystalline Semiconductors Physical Properties and Applications (Heidelberg, Springer, 1985), pp. 223-262. 

The liquid-junction photovoltaic cell has the advantages that the junction between electrolytic solution and semiconductor is formed easily and that polycrystalline semiconductors can be used. The principal disadvantage is that the semiconductor electrode tends to corrode under illumination. The electrochemical nature of the cell allows both production of electricity and generation of chemical products which can be separated, stored, and recombined to recover the stored energy. Liquid-junction cells also have the advantages that are attributed to other photovoltaic devices. Photovoltaic power plants can provide local generation of power on a small scale. The efficiency and cost of solar cells is independent of scale, and overall efficiency is improved by locating the power plant next to the load.72... 

Choi K (2010) Shape effect and shape control of polycrystalline semiconductor electrodes for use in photoelectrochemical cells. J Phys Chem Lett 1 2244-2250... 

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