Cadmium telluride

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Cadmium telluride
Sphalerite-unit-cell-depth-fade-3D-balls.png
CdTe.jpg
Names
Other names
Irtran-6
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.013.773 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 215-149-9
PubChem CID
RTECS number
  • EV3330000
UNII
  • InChI=1S/Cd.Te Yes check.svgY
    Key: RPPBZEBXAAZZJH-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/Cd.Te/rCdTe/c1-2
    Key: RPPBZEBXAAZZJH-UEZHWRJLAD
  • monomer:[Cd]=[Te]
  • crystal form:[TeH+2]12[CdH2-2][TeH+2]3[CdH2-2][TeH+2]([CdH-2]14)[CdH-2]1[Te+2]5([CdH-2]38)[Cd-2]26[TeH+2]2[CdH-2]([Te+2]4)[TeH+2]1[CdH2-2][TeH+2]3[CdH-2]2[Te+2][CdH-2]([TeH+2]6[CdH-2]([TeH+2])[TeH+2]68)[TeH+2]([CdH2-2]6)[CdH-2]35
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 solventsinsoluble
Band gap 1.5 eV (@300 K, direct)
Thermal conductivity 6.2 W·m/m2·K at 293 K
2.67 (@10 μm)
Structure
Zinc blende
F43m
a = 0.648 nm
Thermochemistry
210 J/kg·K at 293 K
Hazards
GHS labelling:
GHS-pictogram-exclam.svg GHS-pictogram-pollu.svg
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
Other anions
Cadmium oxide
Cadmium sulfide
Cadmium selenide
Other cations
Zinc telluride
Mercury telluride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with cadmium sulfide to form a p–n junction solar PV cell.

Applications

CdTe is used to make thin 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 by First Solar. In 2011, around 2 GWp of CdTe solar cells were produced; [4] For more details and discussion see cadmium telluride photovoltaics.

CdTe can be alloyed with mercury to make a versatile infrared detector material (HgCdTe). CdTe alloyed with a small amount of zinc makes an excellent solid-state X-ray and gamma ray detector (CdZnTe).

CdTe is used as an infrared optical material for optical windows and lenses 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 of Irtran-6, but this is obsolete.

CdTe is also applied for electro-optic modulators. It has the greatest electro-optic coefficient of the linear electro-optic effect among II-VI compound crystals (r41=r52=r63=6.8×10−12 m/V).

CdTe doped with chlorine is used as a radiation detector for x-rays, gamma rays, beta particles and alpha 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 and small pixel detectors.

Physical properties

Optical and electronic properties

Fluorescence spectra of colloidal CdTe quantum dots of various sizes, increasing approximately from 2 to 20 nm from left to right. The blue shift of fluorescence is due to quantum confinement. CdTe PlasmaChem spectra-en.svg
Fluorescence spectra of colloidal CdTe quantum dots of various sizes, increasing approximately from 2 to 20 nm from left to right. The blue shift of fluorescence is due to quantum confinement.

Bulk CdTe is transparent in the infrared, from close to its band gap energy (1.5 eV at 300 K, [10] which corresponds to infrared wavelength of about 830 nm) out to wavelengths greater than 20 μm; correspondingly, CdTe is fluorescent at 790 nm. As the size of CdTe crystals are reduced to a few nanometers or less, thus making them CdTe quantum dots, the fluorescence peak shifts through the visible range into the ultraviolet.

Chemical properties

CdTe is insoluble 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.

Toxicology assessment

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 the European 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 the U.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) and First 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]

Availability

At the present time, the prices of the raw materials cadmium and tellurium 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; see Abundances of the elements (data page)). Through improved material 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] See Cadmium 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]

See also

Related Research Articles

<span class="mw-page-title-main">Tellurium</span> Chemical element with atomic number 52 (Te)

Tellurium is a chemical element; it has symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally found in its native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth.

<span class="mw-page-title-main">Photovoltaics</span> Method to produce electricity from solar radiation

Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially used for electricity generation and as photosensors.

<span class="mw-page-title-main">Cadmium sulfide</span> Chemical compound

Cadmium sulfide is the inorganic compound with the formula CdS. Cadmium sulfide is a yellow salt. It occurs in nature with two different crystal structures as the rare minerals greenockite and hawleyite, but is more prevalent as an impurity substituent in the similarly structured zinc ores sphalerite and wurtzite, which are the major economic sources of cadmium. As a compound that is easy to isolate and purify, it is the principal source of cadmium for all commercial applications. Its vivid yellow color led to its adoption as a pigment for the yellow paint "cadmium yellow" in the 1800s.

<span class="mw-page-title-main">Lead(II) sulfide</span> Chemical compound

Lead(II) sulfide is an inorganic compound with the formula PbS. Galena is the principal ore and the most important compound of lead. It is a semiconducting material with niche uses.

The telluride ion is the anion Te2− and its derivatives. It is analogous to the other chalcogenide anions, the lighter O2−, S2−, and Se2−, and the heavier Po2−.

<span class="mw-page-title-main">Mercury cadmium telluride</span> Alloy

Hg1−xCdxTe or mercury cadmium telluride is a chemical compound of cadmium telluride (CdTe) and mercury telluride (HgTe) with a tunable bandgap spanning the shortwave infrared to the very long wave infrared regions. The amount of cadmium (Cd) in the alloy can be chosen so as to tune the optical absorption of the material to the desired infrared wavelength. CdTe is a semiconductor with a bandgap of approximately 1.5 eV at room temperature. HgTe is a semimetal, which means that its bandgap energy is zero. Mixing these two substances allows one to obtain any bandgap between 0 and 1.5 eV.

<span class="mw-page-title-main">Solar cell</span> Photodiode used to produce power from light on a large scale

A solar cell or photovoltaic cell is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect. It is a form of photoelectric cell, a device whose electrical characteristics vary when it is exposed to light. Individual solar cell devices are often the electrical building blocks of photovoltaic modules, known colloquially as "solar panels". Almost all commercial PV cells consist of crystalline silicon, with a market share of 95%. Cadmium telluride thin-film solar cells account for the remainder. The common single-junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts.

Cadmium zinc telluride, (CdZnTe) or CZT, is a compound of cadmium, zinc and tellurium or, more strictly speaking, an alloy of cadmium telluride and zinc telluride. A direct bandgap semiconductor, it is used in a variety of applications, including semiconductor radiation detectors, photorefractive gratings, electro-optic modulators, solar cells, and terahertz generation and detection. The band gap varies from approximately 1.4 to 2.2 eV, depending on composition.

<span class="mw-page-title-main">Infrared detector</span>

An infrared detector is a detector that reacts to infrared (IR) radiation. The two main types of detectors are thermal and photonic (photodetectors).

<span class="mw-page-title-main">Solar panel</span> Assembly of photovoltaic cells used to generate electricity

A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. The electrons flow through a circuit and produce direct current (DC) electricity, which can be used to power various devices or be stored in batteries. Solar panels are also known as solar cell panels, solar electric panels, or PV modules.

<span class="mw-page-title-main">Zinc telluride</span> Chemical compound

Zinc telluride is a binary chemical compound with the formula ZnTe. This solid is a semiconductor material with a direct band gap of 2.26 eV. It is usually a p-type semiconductor. Its crystal structure is cubic, like that for sphalerite and diamond.

<span class="mw-page-title-main">Mercury telluride</span> Topologically insulating chemical compound

Mercury telluride (HgTe) is a binary chemical compound of mercury and tellurium. It is a semi-metal related to the II-VI group of semiconductor materials. Alternative names are mercuric telluride and mercury(II) telluride.

<span class="mw-page-title-main">Zinc phosphide</span> Chemical compound

Zinc phosphide (Zn3P2) is an inorganic chemical compound. It is a grey solid, although commercial samples are often dark or even black. It is used as a rodenticide. Zn3P2 is a II-V semiconductor with a direct band gap of 1.5 eV and may have applications in photovoltaic cells. A second compound exists in the zinc-phosphorus system, zinc diphosphide (ZnP2).

I. M. Dharmadasa is Professor of Applied Physics and leads the Electronic Materials and Solar Energy Group at Sheffield Hallam University, UK. Dharme has worked in semiconductor research since becoming a PhD student at Durham University as a Commonwealth Scholar in 1977, under the supervision of the late Sir Gareth Roberts. His interest in the electrodeposition of thin film solar cells grew when he joined the Apollo Project at BP Solar in 1988. He continued this area of research on joining Sheffield Hallam University in 1990.

<span class="mw-page-title-main">Cadmium telluride photovoltaics</span> Type of solar power cell

Cadmium telluride (CdTe) photovoltaics is a photovoltaic (PV) technology based on the use of cadmium telluride in a thin semiconductor layer designed to absorb and convert sunlight into electricity. Cadmium telluride PV is the only thin film technology with lower costs than conventional solar cells made of crystalline silicon in multi-kilowatt systems.

<span class="mw-page-title-main">Thin-film solar cell</span> Type of second-generation solar cell

Thin-film solar cells are a type of solar cell made by depositing one or more thin layers of photovoltaic material onto a substrate, such as glass, plastic or metal. Thin-film solar cells are typically a few nanometers (nm) to a few microns (μm) thick–much thinner than the wafers used in conventional crystalline silicon (c-Si) based solar cells, which can be up to 200 μm thick. Thin-film solar cells are commercially used in several technologies, including cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and amorphous thin-film silicon.

<span class="mw-page-title-main">5N Plus</span> Canadian materials company

5N Plus is a Canadian producer of high-purity metals and compounds for electronic applications best known as the major supplier of cadmium telluride (CdTe) to First Solar. The company was founded in 1996 and is headquartered in Saint-Laurent, Quebec, Canada. 5N Plus is a leading producer of specialty metals and chemicals, including high-purity metals such as bismuth, indium, and tellurium, as well as other materials such as cadmium, gallium, and selenium. The company's products are used in a range of applications, including electronics, solar energy, and medical devices. 5N Plus has operations in North America, Europe, and Asia and serves customers around the world.

<span class="mw-page-title-main">CZTS</span> Chemical compound

Copper zinc tin sulfide (CZTS) is a quaternary semiconducting compound which has received increasing interest since the late 2000s for applications in thin film solar cells. The class of related materials includes other I2-II-IV-VI4 such as copper zinc tin selenide (CZTSe) and the sulfur-selenium alloy CZTSSe. CZTS offers favorable optical and electronic properties similar to CIGS (copper indium gallium selenide), making it well suited for use as a thin-film solar cell absorber layer, but unlike CIGS (or other thin films such as CdTe), CZTS is composed of only abundant and non-toxic elements. Concerns with the price and availability of indium in CIGS and tellurium in CdTe, as well as toxicity of cadmium have been a large motivator to search for alternative thin film solar cell materials. The power conversion efficiency of CZTS is still considerably lower than CIGS and CdTe, with laboratory cell records of 11.0 % for CZTS and 12.6 % for CZTSSe as of 2019.

Lead tin telluride, also referred to as PbSnTe or Pb1−xSnxTe, is a ternary alloy of lead, tin and tellurium, generally made by alloying either tin into lead telluride or lead into tin telluride. It is a IV-VI narrow band gap semiconductor material.

<span class="mw-page-title-main">Occupational hazards of solar panel installation</span>

The introduction and rapid expansion of solar technology has brought with it a number of occupational hazards for workers responsible for panel installation. Guidelines for safe solar panel installation exist, however the injuries related to panel installation are poorly quantified.

References

  1. ↑ Peter Capper (1994). Properties of Narrow Gap Cadmium-Based Compounds. IET. pp. 39–. ISBN   978-0-85296-880-2 . Retrieved 1 June 2012.
  2. 1 2 Nomination of Cadmium Telluride to the National Toxicology Program (PDF) (Report). United States Department of Health and Human Services. 2003-04-11.
  3. 1 2 3 NIOSH Pocket Guide to Chemical Hazards. "#0087". National Institute for Occupational Safety and Health (NIOSH).
  4. 1 2 "Photovoltaics report" (PDF). Archived from the original (PDF) on 2012-11-05.
  5. ↑ "Introduction". Chalcogenide Photovoltaics. 2011. pp. 1–8. doi:10.1002/9783527633708.ch1. ISBN   9783527633708.
  6. ↑ "Cadmium Telluride".
  7. ↑ P. Capper (1994). Properties of Narrow-Gap Cadmium-Based Compounds. London, UK: INSPEC, IEE. ISBN   978-0-85296-880-2.
  8. ↑ Veale, M. C.; Kalliopuska, J.; Pohjonen, H.; Andersson, H.; Nenonen, S.; Seller, P.; Wilson, M. D. (2012). "Characterization of M-π-n CdTe pixel detectors coupled to HEXITEC readout chip". Journal of Instrumentation. 7 (1): C01035. Bibcode:2012JInst...7C1035V. doi: 10.1088/1748-0221/7/01/C01035 .
  9. ↑ Palmer, D W (March 2008). "Properties of II-VI Compound Semiconductors". Semiconductors-Information.
  10. ↑ Fonthal, G.; et al. (2000). "Temperature dependence of the band gap energy of crystalline CdTe". J. Phys. Chem. Solids. 61 (4): 579–583. Bibcode:2000JPCS...61..579F. doi:10.1016/s0022-3697(99)00254-1.
  11. ↑ Solubility is below 0.1mg/L which equals a classification as insoluble- reference, "ECHA Substance Registration" Archived 2013-12-13 at archive.today
  12. ↑ "Cadmium Telluride". Archived from the original on 2013-12-13. Retrieved 2013-12-13.
  13. ↑ S. Kaczmar (2011). "Evaluating the read-across approach on CdTe toxicity for CdTe photovoltaics" (PDF).[ permanent dead link ]
  14. ↑ "Scientific Comment of Fraunhofer to Life Cycle Assessement[sic] of CdTe Photovoltaics". Fraunhofer Center for Silicon Photovoltaics CSP. Archived from the original on 2013-12-13.
  15. ↑ V. Fthenakis; K. Zweibel (2003). "CdTe PV: Real and Perceived EHS Risks" (PDF). National Renewable Energy Laboratory.
  16. ↑ "Cadmium telluride - Brief Profile - ECHA". European Chemicals Agency. 2020.
  17. ↑ M. Marwede; A. Reller (2012). "Future recycling flows of tellurium from cadmium telluride photovoltaic waste" (PDF). Resources, Conservation and Recycling. 69: 35–49. doi:10.1016/j.resconrec.2012.09.003.
  18. ↑ Fthenakis, V.M. (2012). "Sustainability metrics for extending thin-film photovoltaics to terawatt levels". MRS Bulletin. 37 (4): 425–430. doi: 10.1557/mrs.2012.50 .
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