THERMOELECTRIC TE MATERIALS

IMPORTANT MATERIALS APPLICATIONS III PHOTOVOLTAIC (SOLAR) CELLS 

The increasingly volatile prices and availability of gasoline and natural gas, and the recent British Petroleum oil spill disaster has brought about a heightened awareness of our dependence on nonrenewable resources. Currently, over 90% of the US electricity supply comes from the combustion of fossil fuels i.e., coal, oil, and natural gas) and nuclear power generation. 

While the US coal reserve is estimated at 290 billion tons (enough to last another 230 years at current production levels), there is an increased concern about the adverse environmental effects associated with its combustion, namely SO NO and CO2 emissions. With the energy needs of our world likely to double within our 

While it is important to control the stoichiometry of each layer to adjust their bandgaps, it is equally important to have as few interfacial mismatches as possible. That is, each layer must be epitaxially grown to ensure that the lattice constants are perfectly matched. It has been shown that a lattice mismatch of only ca. 0.01% is enough to cause significant electron-hole recombinations, resulting in lower cell efficiency. CVD is the method of choice for the fabrication of these multilayer devices as you might expect, cells of this variety are relatively quite expensive. 

Note the solar market has been growing at a rate of 40% ear in recent years, as compared to 4—6%/ year for the semiconductor market. For more informatirm on markets and production figures, see http //www.aiche.org/cep (Aug. 2008 issue). 

Where a is the Seebeck coefficient jiVjK 1-10 for metals, 150-250 for semiconductors) the fj, electrical conductivity and X is the thermal conductivity. 

Funahashi, R. MRS Bull. 2006, 31, 206. Copyright 2006 Materials Research Society. 

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In the last decade, much effort has been expended on developing novel thermoelectric (TE) materials of increased intrinsic conversion efficiency [9] at same time, the design of the system architecture plays an important role in optimizing the thermal exchange and in maximizing the conversion performance [10]. For that reason, in this section we report an example of a detailed thermal management analysis with the heat re-flowed in the system. 

Abstract We investigate metal oxides as thermoelectric (TE) materials and further as... 

Figure 4.1 presents a schematic description of a TEG. n- and p-type thermoelectric (TE) materials are electrically connected in series, and thermally connected in parallel between two plates submitted to a temperature gradient AT =T T. ... 

In summary, CPs offer numerous advantages over inorganic semiconductors for thermoelectric applications because of their unique properties. However, the poor electrical transport properties have impeded their practical application as TE materials in the past. Recent studies indicate that incorporating the inorganic nanoparticle into polymer matrix is an effective way to improve the electrical transport properties of CPs, including electrical conductivity and Seebeck coefficient, while keep the thermal conductivity at low level simultaneously. Consequently, the power factors of most CP-based nanocomposites are about 2 3 orders of magnitude higher than those of conventional pure CPs and the maximum ZT value is up to 0.1 at present. 

In this chapter, we have tried to give an overview on the emerging field of thermoelectric (TE) oxides. Dealing with this class of materials, the first important conclusion lies in the physics difference between the p- and n-type TE oxides. As a large part of that research has been devoted to the p-type NaxCo02 layer cobaltates and derived phases, one major output lies in the important role played by the electronic correlations. Usually the physics of conventional TEs is based on models of degenerate semiconductors and thus strongly correlated materials have opened new perspectives for the search of TE materials. 

At present, the elements used in the formation of compounds by EC-ALE include the chalcogenides S, Se, and Te the pnictides As and Sb the group three metals Ga and In the group II metals Zn, Cd, and Hg as well as Cu, and Co. The range of compounds accessible by EC-ALE is not clear. The majority of work has been performed on II VI compounds (Table 1). The III-V compounds InAs and InSb have recently been formed, and the first deposits of a III-VI compound, InSe, have been made [151], In addition, Shannon et al. have begun studies of CoSb [152] with the intent of forming thermoelectric materials. 

Figure 4.49. Unit cell of Bi2Te3 - a widely studied thermoelectric material. The blue atoms are Bi, and the pink atoms are Te. Reproduced with permission from Tritt, T. M. Subramanian, M. A. MRS Bull. 2006, 31, 188. Copyright 2006 Materials Research Society.

The thermoelectric potential, te> is due to the heat transport of the electrons and arises if an electron conductor (usually a wire) is in nonisothermal condition. Eje is a function of the temperature gradient and, for the most common wire materials, is usually up to a few millivolts. Eje can be calculated over a wide range of temperatures for most of the wire materials such as Pt, Ag, Cu, Fe, Ni, and so on [13]. 

Fig.l. Optimal functions of thermoelectric material inhomogeneity n-type Bi2Te2jSeo.i + (0,09... O.OSjCdCh p-type Bio.sSbi.sTe + 4% Te... 

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