Cadmium Telluride CdTe

The thermodynamic principles of the Cd-Te-water system are depicted in the Pourbaix diagram of Fig. 3.5 [82]. The corresponding electrochemical reactions of CdTe reduction and oxidation are shown in Table 3.1. 

The work of Verbrugge and Tobias on CdTe [8] comprises a comprehensive source of information about the electrochemistry of the compound and its components. Deposition features are reviewed, and thermodynamic, transport, and kinetic parameters for cadmium and tellurium deposition are reported. 

The reaction mechanism in acidic tellurite baths has been the subject of considerable debate in the literature concerning mostly the number of exchanging electrons 

CdTe -b 2H2O CdTe -b 2H2O CdTe -b 3H2O CdTe -b 3H2O CdTe -b 5H2O CdTe -b 5H2O  

Cathodic photo-currents observed during the deposition of CdTe have been interpreted as evidence for p-type conductivity [90]. Verbrugge and Tobias [91] showed 

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A prime contender for leading thin film technology as applied to solar cells is cadmium telluride (CdTe). Its bandgap is almost ideal for use as a solar cell for energy conversion from the Sun s spectrum. Here, CdTe and cadmium sulfide (CdS) are used to produce a low cost thin film solar cell... 

Various inorganic semiconductors (p-type and/or n-type nonoxide semiconducting materials) sucb as amorphous or crystalline silicon (a-Si or c-Si), gallium arsenide (GaAs), cadmium telluride (CdTe), gallium phosphide (GaP), indium phosphide (InP), copper... 

The measurement of vibrational circular dichroism was confined to the region below 15 pm resulting from the transmittance characteristics of the photoelastic modulator made from zink selenide (ZnSe). This was changed by the employment of a photoelastic modulator made from cadmium telluride (CdTe) with sufficient transparency down to about 300 cm. ... 

The basic structure of polycrystalline cadmium telluride (CdTe) thin-film cells has a glass superstrate and a layer of TCO as front contact, a near-transparent n-type cadmium sulfide (CdS) window layer, p-type CdTe, and a metallic rear contact. The CdTe is usually deposited by three families of techniques. In the first group (vapor transport deposition, close space sublimation, physical vapor deposition, and sputtering) elemental vapors of Cd and Te condense and react on the substrate. In the second (electrodeposition), Cd + and HTe02" ions in acidic electrolyte are galvanically reduced at the surface ... 

Many other systems based on different nanoparticles have been introduced, such as copper indium disulfide (CuInS2) [263-265], copper indium diselenide (CuInSe2) [266,267], cadmium telluride (CdTe) [268], lead sulfide (PbS) [269,270], lead selenide (PdSe) [271], and mercury telluride (HgTe) [272]. Some of these systems show enhanced spectral response well into the infrared part of the solar spectrum [271,272]. In most cases the absorption of the nanocrystals was, however, quantitatively small as compared to the conjugated polymers. 

Cadmium telluride, CdTe, lakes the zinc blende structure (Figure 12.26) with a unit cell edge length of 6.49 A. There are four cadmium atoms and four teUurium atoms per unit cell How many of each type of atom are there in a cubic crystal with an edge length of 5.00 nm ... 

Theoretical conversion efficiencies of photovoltaic systems depend on the semiconductor materials used in the cells and on the ambient tanperatuie. The materials currently used to make photovoltaic cells can be grouped into three broad categories 1) expensive, efficient monocrystalline silicon, 2) less efficient but much lower cost polycrystalline silicon, and 3) the lowest cost and poorest performer, amorphous silicon material. Conversion efficiencies of commercial polycrystaUine silicon cells are 10 to 15 percent. Now the primary development areas are in how to use monocrystalline silicon with solar concentrators and making thin-film cells by depositing a 5- to 20-micron film of silicon onto an inexpensive substrate, because the estimated efficiency of these cells is above 20 percent. Work is ongoing with other materials, including amorphous silicon (a-Si), copper indium diselenide (CuInSe2 or CIS) and related materials, and cadmium telluride (CdTe). 

Compared to homojunction stmcture amorphous silicon thin-film cells use a P-I-N hetrojunction stmcture, whereas cadmium telluride (CdTe) cells utilize a N-I-P arrangement. The overall picture embraces a three-layer sandwich with a middle intrinsic (/-type or undoped) layer between an N-t) e layer and a P-type layer (Fig. 3b). Multiple junction cells have... 

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