View source for Cadmium telluride

{{Short description|Semiconductor chemical compound used in solar cells
}}
{{Lead too short|date=May 2023}}
{{Use American English|date=January 2019}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 477001563
| Name = Cadmium telluride
| ImageFile1 = Sphalerite-unit-cell-depth-fade-3D-balls.png
| ImageName1 =
| ImageFile2 = CdTe.jpg
| ImageName2 = Cadmium telluride
| OtherNames = Irtran-6
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 82622
| InChI = 1/Cd.Te/rCdTe/c1-2
| SMILES = [Cd]=[Te]
| SMILES_Comment = monomer
| SMILES1 = [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
| SMILES1_Comment = crystal form
| InChIKey = RPPBZEBXAAZZJH-UEZHWRJLAD
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Cd.Te
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = RPPBZEBXAAZZJH-UHFFFAOYSA-N
| CASNo = 1306-25-8
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 91501
| RTECS = EV3330000
| EINECS = 215-149-9
| UNII = STG188WO13
}}
|Section2={{Chembox Properties
| Cd=1 | Te=1
| MolarMass = 240.01 g/mol
| Density = 5.85 g·cm<sup>−3</sup><ref name="Capper1994">{{cite book|author=Peter Capper|title=Properties of Narrow Gap Cadmium-Based Compounds|url=https://books.google.com/books?id=WAhC3hGYQ7UC&pg=PA39|access-date=1 June 2012|year=1994|publisher=IET|isbn=978-0-85296-880-2|pages=39–}}</ref>
| Solubility = insoluble
| Solvent = other solvents
| SolubleOther = insoluble
| MeltingPtC = 1041
| MeltingPt_ref = <ref name="NIH2003">{{cite report |url=https://ntp.niehs.nih.gov/ntp/htdocs/chem_background/exsumpdf/cdte_508.pdf |title=Nomination of Cadmium Telluride to the National Toxicology Program |publisher=United States Department of Health and Human Services |date=2003-04-11}}</ref>
| BoilingPtC = 1050
| BandGap = 1.5 eV (@300 K, direct)
| RefractIndex = 2.67 (@10 μm)
| ThermalConductivity = 6.2 W·m/m<sup>2</sup>·K at 293 K
}}
|Section3={{Chembox Structure
| CrystalStruct = [[Zincblende (crystal structure)|Zinc blende]]
| SpaceGroup = F{{overline|4}}3m
| LattConst_a = 0.648 nm
}}
| Section4 = {{Chembox Thermochemistry
| Thermochemistry_ref =
| HeatCapacity = 210 J/kg·K at 293 K
| Entropy =
| DeltaHf =
| DeltaGf =
| DeltaHc =
}}
|Section7={{Chembox Hazards
| ExternalSDS =
| GHSPictograms = {{GHS07}}{{GHS09}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|302|312|332|410|411}}
| PPhrases = {{P-phrases|261|264|270|271|273|280|301+312|302+352|304+312|304+340|312|322|330|363|391|501}}
| REL = Ca<ref name=PGCH>{{PGCH|0087}}</ref>
| PEL = [1910.1027] TWA 0.005 mg/m<sup>3</sup> (as Cd)<ref name=PGCH/>
| IDLH = Ca [9 mg/m<sup>3</sup> (as Cd)]<ref name=PGCH/>
}}
|Section8={{Chembox Related
| OtherAnions = [[Cadmium oxide]]<br/>[[Cadmium sulfide]]<br/>[[Cadmium selenide]]
| OtherCations = [[Zinc telluride]]<br/>[[Mercury telluride]]
}}
}}
'''Cadmium telluride''' (CdTe) is a stable [[crystal]]line [[Chemical compound|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 ==
{{See also|Cadmium telluride photovoltaics}}
CdTe is used to make [[thin film solar cell]]s, accounting for about 8% of all solar cells installed in 2011.<ref name="Fraunhofer Institute">{{cite web|url=http://www.ise.fraunhofer.de/de/downloads/pdf-files/aktuelles/photovoltaics-report.pdf|title=Photovoltaics report|url-status=dead|archive-url=https://web.archive.org/web/20121105154721/http://www.ise.fraunhofer.de/de/downloads/pdf-files/aktuelles/photovoltaics-report.pdf|archive-date=2012-11-05}}</ref> They are among the lowest-cost types of solar cell,<ref>{{Cite book | doi=10.1002/9783527633708.ch1| chapter=Introduction| title=Chalcogenide Photovoltaics| pages=1–8| year=2011| isbn=9783527633708}}</ref> 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 [[Watt-peak|GW<sub>p</sub>]] of CdTe solar cells were produced;<ref name="Fraunhofer Institute">{{cite web|url=http://www.ise.fraunhofer.de/de/downloads/pdf-files/aktuelles/photovoltaics-report.pdf|title=Photovoltaics report|url-status=dead|archive-url=https://web.archive.org/web/20121105154721/http://www.ise.fraunhofer.de/de/downloads/pdf-files/aktuelles/photovoltaics-report.pdf|archive-date=2012-11-05}}</ref> For more details and discussion see [[cadmium telluride photovoltaics]].
CdTe can be [[alloy]]ed with [[mercury (element)|mercury]] to make a versatile [[infrared detector]] material ([[Mercury(II) cadmium(II) telluride|HgCdTe]]). CdTe alloyed with a small amount of [[zinc]] makes an excellent solid-state [[X-ray]] and [[gamma ray]] detector ([[cadmium zinc telluride|CdZnTe]]).
CdTe is used as an [[infrared]] optical material for [[optical window]]s and [[lens (optics)|lenses]] and is proven to provide a good performance across a wide range of temperatures.<ref name="University of Reading">{{cite web|url=http://www.reading.ac.uk/infrared/library/infraredmaterials|title=Cadmium Telluride}}</ref> 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 modulator]]s. It has the greatest electro-optic coefficient of the linear [[electro-optic effect]] among II-VI compound crystals (r<sub>41</sub>=r<sub>52</sub>=r<sub>63</sub>=6.8×10<sup>−12</sup> m/V).
CdTe doped with [[chlorine]] is used as a radiation detector for x-rays, gamma rays, [[beta particle]]s and [[alpha particle]]s. CdTe can operate at room temperature allowing the construction of compact detectors for a wide variety of applications in nuclear spectroscopy.<ref>{{cite book|title= Properties of Narrow-Gap Cadmium-Based Compounds| author = P. Capper | publisher = INSPEC, IEE| location= London, UK| year = 1994| isbn=978-0-85296-880-2}}</ref> 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&nbsp;cm<sup>2</sup>/V·s, which result in high intrinsic μτ (mobility-lifetime) product and therefore high degree of charge collection and excellent spectral resolution.<ref>{{cite journal|title=Characterization of M-π-n CdTe pixel detectors coupled to HEXITEC readout chip|journal=Journal of Instrumentation |volume=7 |issue=1 |pages=C01035 | doi=10.1088/1748-0221/7/01/C01035|year=2012 |last1=Veale |first1=M. C. |last2=Kalliopuska |first2=J. |last3=Pohjonen |first3=H. |last4=Andersson |first4=H. |last5=Nenonen |first5=S. |last6=Seller |first6=P. |last7=Wilson |first7=M. D. |bibcode=2012JInst...7C1035V |doi-access=free }}</ref> Due to the poor charge transport properties of holes, ~100&nbsp;cm<sup>2</sup>/V·s, single-carrier-sensing detector geometries are used to produce high resolution spectroscopy; these include coplanar grids, [[Frisch grid|Frisch-collar]] detectors and [[HEXITEC|small pixel]] detectors.
== Physical properties ==
*[[Thermal expansion coefficient]]: 5.9×10<sup>−6</sup>/K at 293 K<ref>{{cite web |url=http://www.semiconductors.co.uk/propiivi5410.htm |first=D W |last=Palmer |title=Properties of II-VI Compound Semiconductors |publisher=Semiconductors-Information |date=March 2008}}</ref>
*[[Young's modulus]]: 52 GPa
*[[Poisson ratio]]: 0.41
=== Optical and electronic properties ===
[[Image:CdTe PlasmaChem spectra-en.svg|thumb|350px|left|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 [[Potential well|quantum confinement]].]]
Bulk CdTe is [[Transparency (optics)|transparent]] in the [[infrared]], from close to its band gap energy (1.5 eV at 300 K,<ref>{{cite journal |journal=J. Phys. Chem. Solids |first=G. |last=Fonthal |title=Temperature dependence of the band gap energy of crystalline CdTe|doi=10.1016/s0022-3697(99)00254-1|volume=61 |issue=4 |pages=579–583 |date=2000|display-authors=etal|bibcode=2000JPCS...61..579F }}</ref> which corresponds to infrared wavelength of about 830&nbsp;nm) out to [[wavelength]]s greater than 20&nbsp;μm; correspondingly, CdTe is [[fluorescence|fluorescent]] at 790&nbsp;nm. As the size of CdTe crystals are reduced to a few nanometers or less, thus making them CdTe [[quantum dot]]s, the fluorescence peak shifts through the visible range into the ultraviolet.
== Chemical properties ==
CdTe is [[insoluble]] in water.<ref name=foot11>Solubility is below 0.1mg/L which equals a classification as insoluble- reference, "ECHA Substance Registration"[http://apps.echa.europa.eu/registered/data/dossiers/DISS-dffb4072-e283-47ae-e044-00144f67d031/DISS-dffb4072-e283-47ae-e044-00144f67d031_DISS-dffb4072-e283-47ae-e044-00144f67d031.html] {{Webarchive|url=https://archive.today/20131213155005/http://apps.echa.europa.eu/registered/data/dossiers/DISS-dffb4072-e283-47ae-e044-00144f67d031/DISS-dffb4072-e283-47ae-e044-00144f67d031_DISS-dffb4072-e283-47ae-e044-00144f67d031.html |date=2013-12-13 }}</ref> CdTe has a high melting point of {{convert|1041|C}} with evaporation starting at {{convert|1050|C}}.<ref name="ECHA Substance Registration">{{cite web|title=Cadmium Telluride|url=http://apps.echa.europa.eu/registered/data/dossiers/DISS-dffb4072-e283-47ae-e044-00144f67d031/DISS-dffb4072-e283-47ae-e044-00144f67d031_DISS-dffb4072-e283-47ae-e044-00144f67d031.html|access-date=2013-12-13|archive-url=https://archive.today/20131213155005/http://apps.echa.europa.eu/registered/data/dossiers/DISS-dffb4072-e283-47ae-e044-00144f67d031/DISS-dffb4072-e283-47ae-e044-00144f67d031_DISS-dffb4072-e283-47ae-e044-00144f67d031.html|archive-date=2013-12-13|url-status=dead}}</ref> 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.<ref>{{cite web |url=ftp://ftp.co.imperial.ca.us/icpds/eir/campo-verde-solar/final/evaluating-toxicity.pdf |title=Evaluating the read-across approach on CdTe toxicity for CdTe photovoltaics |author=S. Kaczmar |year=2011 }}{{Dead link|date=July 2020 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
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.<ref>{{cite web |url= http://www.csp.fraunhofer.de/presse-und-veranstaltungen/details/id/47/ |title= Scientific Comment of Fraunhofer to Life Cycle Assessement{{sic|nolink=yes}} of CdTe Photovoltaics |publisher= Fraunhofer Center for Silicon Photovoltaics CSP |url-status= dead |archive-url= https://web.archive.org/web/20131213174834/http://www.csp.fraunhofer.de/presse-und-veranstaltungen/details/id/47/ |archive-date= 2013-12-13 }}</ref> 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.<ref>{{cite web|url=http://www.nrel.gov/docs/fy03osti/33561.pdf |title=CdTe PV: Real and Perceived EHS Risks |author1=V. Fthenakis |author2=K. Zweibel |publisher= National Renewable Energy Laboratory |year=2003}}</ref>
A document hosted by the U.S. National Institutes of Health<ref name="NIH2003" /> dated 2003 discloses the following:
{{blockquote|text=
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.<ref>{{cite web|url=https://echa.europa.eu/brief-profile/-/briefprofile/100.013.773|title=Cadmium telluride - Brief Profile - ECHA|publisher= European Chemicals Agency|year=2020}}</ref>
== 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.<ref>{{cite journal|author1=M. Marwede |author2=A. Reller |date=2012 |title=Future recycling flows of tellurium from cadmium telluride photovoltaic waste|volume=69 |pages=35–49|journal=Resources, Conservation and Recycling|doi=10.1016/j.resconrec.2012.09.003|url=https://depositonce.tu-berlin.de/bitstream/11303/7375/3/2012_marwede_et-al.pdf}}</ref> 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.<ref>{{cite journal | last1 = Fthenakis | first1 = V.M. | year = 2012 | title = Sustainability metrics for extending thin-film photovoltaics to terawatt levels | journal = MRS Bulletin | volume = 37 | issue = 4| pages = 425–430 | doi = 10.1557/mrs.2012.50 | doi-access = free }}</ref>
== See also ==
{{div col|colwidth=22em}}
*[[Cadmium selenide]]
*[[Cadmium telluride photovoltaics]]
*[[Cadmium zinc telluride]]
*[[First Solar]]
*[[Mercury telluride]]
*[[Mercury(II) cadmium(II) telluride]]
*[[Zinc telluride]]
{{div col end}}
== References ==
{{Reflist|30em}}
== External links ==
*[https://web.archive.org/web/20070125125715/http://www.sttic.com.ru/lpcbc/DANDP/cdte_adv.html CdTe page on the web-site of the Institute of Solid State Physics of the Russian Academy of Sciences (html)]
*[http://www.reading.ac.uk/infrared/library/infraredmaterials/ir-infraredmaterials-cdte.asp Optical properties] University of Reading, Infrared Multilayer Laboratory
*[https://web.archive.org/web/20070125125715/http://www.sttic.com.ru/lpcbc/DANDP/cdte_adv.html CdTe: single crystals, grown by HPVB and HPVZM techniques; windows, substrates, electrooptical modulators. Infrared transmittance spectrum. MSDS.]
*[https://web.archive.org/web/20061210213049/http://www.npi.gov.au/database/substance-info/profiles/17.html National Pollutant Inventory – Cadmium and compounds]
*[https://web.archive.org/web/20150602085154/http://www.ispoptics.com/new_webpage/MSDS%20CdTe.doc MSDS at ISP optics.com] (doc)
*[https://web.archive.org/web/20080309103941/http://www.espimetals.com/msds's/cadmiumtelluride.pdf MDSD at espimetals.com] (pdf)
*[https://web.archive.org/web/20150602085154/http://www.ispoptics.com/new_webpage/MSDS%20CdTe.doc Material Safety data Sheet] on isp optics web site (MS Word doc)
{{Cadmium compounds}}
{{Tellurides}}
{{Photovoltaics}}
{{Authority control}}
{{DEFAULTSORT:Cadmium Telluride}}
[[Category:Cadmium compounds]]
[[Category:Tellurides]]
[[Category:Photovoltaics]]
[[Category:II-VI semiconductors]]
[[Category:Zincblende crystal structure]]