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| Names | |
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| Other names Irtran-6 | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider |
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| ECHA InfoCard | 100.013.773 |
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| Properties | |
| CdTe | |
| Molar mass | 240.01 g/mol |
| Density | 5.85 g·cm−3[1] |
| Melting point | 1,041 °C (1,906 °F; 1,314 K)[2] |
| Boiling point | 1,050 °C (1,920 °F; 1,320 K) |
| insoluble | |
| Solubility in other solvents | insoluble |
| Band gap | 1.5 eV (@300 K, direct) |
| Thermal conductivity | 6.2 W·m/m2·K at 293 K |
Refractive index (nD) | 2.67 (@10 μm) |
| Structure | |
| Zinc blende | |
| F43m | |
a = 0.648 nm | |
| Thermochemistry | |
| 210 J/kg·K at 293 K | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H302,H312,H332,H410,H411 | |
| P261,P264,P270,P271,P273,P280,P301+P312,P302+P352,P304+P312,P304+P340,P312,P322,P330,P363,P391,P501 | |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | [1910.1027] TWA 0.005 mg/m3 (as Cd)[3] |
REL (Recommended) | Ca[3] |
IDLH (Immediate danger) | Ca [9 mg/m3 (as Cd)][3] |
| Related compounds | |
Otheranions | Cadmium oxide Cadmium sulfide Cadmium selenide |
Othercations | Zinc telluride Mercury telluride |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Cadmium telluride (CdTe) is a stablecrystallinecompound formed fromcadmium andtellurium. It is mainly used as thesemiconducting material incadmium telluride photovoltaics and aninfraredoptical window. It is usually sandwiched withcadmium sulfide to form ap–n junction solar PV cell.
CdTe is used to makethin film solar cells, accounting for about 8% of all solar cells installed in 2011.[4] They are among the lowest-cost types of solar cell,[5] although a comparison of total installed cost depends on installation size and many other factors, and has changed rapidly from year to year. The CdTe solar cell market is dominated byFirst Solar. In 2011, around 2GWp of CdTe solar cells were produced;[4] For more details and discussion seecadmium telluride photovoltaics.
CdTe can bealloyed withmercury to make a versatileinfrared detector material (HgCdTe). CdTe alloyed with a small amount ofzinc makes an excellent solid-stateX-ray andgamma ray detector (CdZnTe).
CdTe is used as aninfrared optical material foroptical windows andlenses and is proven to provide a good performance across a wide range of temperatures.[6] An early form of CdTe for IR use was marketed under the trademarked name ofIrtran-6, but this is obsolete.
CdTe is also applied forelectro-optic modulators. It has the greatest electro-optic coefficient of the linearelectro-optic effect among II-VI compound crystals (r41=r52=r63=6.8×10−12 m/V).
CdTe doped withchlorine is used as a radiation detector for x-rays, gamma rays,beta particles andalpha particles. CdTe can operate at room temperature allowing the construction of compact detectors for a wide variety of applications in nuclear spectroscopy.[7] The properties that make CdTe superior for the realization of high performance gamma- and x-ray detectors are high atomic number, large bandgap and high electron mobility ~1100 cm2/V·s, which result in high intrinsic μτ (mobility-lifetime) product and therefore high degree of charge collection and excellent spectral resolution.[8] Due to the poor charge transport properties of holes, ~100 cm2/V·s, single-carrier-sensing detector geometries are used to produce high resolution spectroscopy; these include coplanar grids,Frisch-collar detectors andsmall pixel detectors.
Bulk CdTe istransparent in theinfrared, from close to its band gap energy (1.5 eV at 300 K,[10] which corresponds to infrared wavelength of about 830 nm) out towavelengths greater than 20 μm; correspondingly, CdTe isfluorescent at 790 nm. As the size of CdTe crystals are reduced to a few nanometers or less, thus making them CdTequantum dots, the fluorescence peak shifts through the visible range into the ultraviolet.
CdTe isinsoluble in water.[11] CdTe has a high melting point of 1,041 °C (1,906 °F) with evaporation starting at 1,050 °C (1,920 °F).[12] CdTe has a vapor pressure of zero at ambient temperatures. CdTe is more stable than its parent compounds cadmium and tellurium and most other Cd compounds, due to its high melting point and insolubility.[13]
Cadmium telluride is commercially available as a powder, or as crystals. It can be made into nanocrystals.
The compound CdTe has different qualities than the two elements, cadmium and tellurium, taken separately. CdTe has low acute inhalation, oral, and aquatic toxicity, and is negative in the Ames mutagenicity test. Based on notification of these results to theEuropean Chemicals Agency (ECHA), CdTe is no longer classified as harmful if ingested nor harmful in contact with skin, and the toxicity classification to aquatic life has been reduced.[14] Once properly and securely captured and encapsulated, CdTe used in manufacturing processes may be rendered harmless. Current CdTe modules pass the U.S. EPA's Toxicity Characteristic Leaching Procedure (TCLP) test, designed to assess the potential for long-term leaching of products disposed in landfills.[15]
A document hosted by the U.S. National Institutes of Health[2] dated 2003 discloses the following:
Brookhaven National Laboratory (BNL) and theU.S. Department of Energy (DOE) are nominating Cadmium Telluride (CdTe) for inclusion in the National Toxicology Program (NTP). This nomination is strongly supported by the National Renewable Energy Laboratory (NREL) andFirst Solar Inc. The material has the potential for widespread applications in photovoltaic energy generation that will involve extensive human interfaces. Hence, we consider that a definitive toxicological study of the effects of long-term exposure to CdTe is a necessity.
According to the classification provided by companies to the European Chemicals Agency (ECHA) in REACH registrations, it is still harmful to aquatic life with long lasting effects.
Additionally, the classification provided by companies to ECHA notifications classifies it as very toxic to aquatic life with long lasting effects, very toxic to aquatic life, harmful if inhaled or swallowed and is harmful in contact with skin.[16]
At the present time, the prices of the raw materialscadmium andtellurium are a negligible proportion of the cost of CdTe solar cells and other CdTe devices. However, tellurium is a relatively rare element (1–5 parts per billion in the Earth's crust; seeAbundances of the elements (data page)). Through improvedmaterial efficiency and increased PV recycling systems, the CdTe PV industry has the potential to fully rely on tellurium from recycled end-of-life modules by 2038.[17] SeeCadmium telluride photovoltaics for more information. Another study shows that CdTe PV recycling will add a significant secondary resource of Te which, in conjunction with improved material utilization, will enable a cumulative capacity of about 2 TW by 2050 and 10 TW by the end of the century.[18]
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