cadmium telluride structure

CdTe layers may be grown by a variety of vacuum and nonvacuum methods classified into high temperature and low temperature processes and resulting typical thicknesses between 2 and 6 μm [8,10,13]. The hexagonal wurtzite structure of ZnO, CdS, CdSe, and of ZnS above its transition temperature, also Cadmium telluride (CdTe) (Bonnet (2012))is a direct-bandgap semiconductor with that bandgap well matched to the solar spectrum.CdTe thin-film laboratory cell efficiency of 18.3% has been achieved, and the record module efficiency currently stands at 15.3%. Early commercial CdTe modules have shown some change (sometimes an initial improvement, but also degradation) in performance. At the same time it is known that ellipsometric data sensitivity to the thin details of the reflective system structure is the highest in the fundamental absorption range of semiconductors, which is caused by intrinsic electron transitions between energy bands. Potential restrictions on market growth are the toxicity of cadmium and limited global supply of tellurium. CdTe always grows as a stoichiometric compound that is much less toxic than Cd metal. The same peculiarities as for films on silicon substrates could be checked out. The physical state in which the Cd compound is used and/or released to the environment is another determinant of risk. There is no sense to cite detailed data about the volume fraction of impurities in the outer layer of films due to sufficiently large errors in two-layer model calculation. Semiconductor films are widely used in various sectors of micro- and optoelectronics for construction of signal transmission devices; thin film electroluminescent devices based on cadmium telluride are used as emitters; CdTe films serve as protecting coatings on the surface of luminous energy receivers in the IR spectral range. The typical structure of the CdS/CdTe device is presented in Figure 7, and is composed of five different layers: (1) the glass substrate; (2) a transparent and conducting oxide (TCO) which acts as a front contact; (3) a CdS film which is the so-called window layer; (4) a CdTe film which is the absorber layer made on top of CdS; (5) the metal back contact on top of the CdTe layer. The substrate configuration has however been reconsidered and the development of a novel doping method allowed solar cell efficiencies close to 14% [12]. That is why it is difficult to do without initial possible assumption concerning the system structure that simplifies procedure of parameters determination. No comparisons with the parent Cd and Te compounds have been made. (2013). The authors declare that there is no conflict of interests regarding the publication of this paper. UNSW catalog of solar cell drawings. No comparisons were made with the parent Cd and Te substances. According to AFM data, there is more or less developed relief on the surface of the films grown using the vacuum “hot-wall” epitaxy method; this fact indicates availability of a rather complex film structure. In general, the hierarchy includes engineering controls, personal protective equipment, and work practices. Similarly, operations involving volatile or soluble Cd compounds (e.g., CdCl2) must be more closely scrutinized. Thus, the thickness of inner layer that is the layer of hard-grained cadmium telluride does not exceed 40 nm (samples F3 and F9). One would not expect to encounter losses at such a relatively low thickness such as 8 μm, when dealing with Si for example (which is typically >100 μm thick), but CdTe suffers from low carrier lifetimes of typically <10 ns [34]. Search results for Cadmium Telluride at Sigma-Aldrich. Films were grown separately for fixed times: 6, 10, and 14 minutes. Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. In addition, the index of extinction values can appreciably exceed the index of extinction for bulk matter. However, reducing the thickness too much often leads to reduced VOC and FF. Specification of the samples is given in Table 1. They are mostly faulted; the thickness of bulk cadmium telluride inner layer is 5 nm (sample F5) and, Advances in Materials Science and Engineering, http://solarlove.org/top-solar-module-manufacturers-2013/, G. K. M. Thutupalli and S. G. Tomlin, “The optical properties of thin films of cadmium and zinc selenides and tellurides,”, B. R. Mehta, S. Kumar, K. Singh, and K. L. Chopra, “Application of spectroscopic ellipsometry to study the effect of surface treatments on cadmium telluride films,”, S. Sirohi, V. Kumar, and T. P. Sharma, “Optical, structural and electrical properties of CdTe sintered films,”, Y. Laaziz, A. Bennouna, N. Chahboun, A. Outzourhit, and E. L. Ameziane, “Optical characterization of low optical thickness thin films from transmittance and back reflectance measurements,”, M. Rusu and G. G. Rusu, “On the optical properties of evaporated CdTe thin films,”, P. D. Paulson and X. Mathew, “Spectroscopic ellipsometry investigation of optical and interface properties of CdTe films deposited on metal foils,”, F. C. Peiris, Z. J. Weber, Y. Chen, and G. Brill, “Optical properties of CdSe, V. Odarych, A. Sarsembaeva, F. F. Sizov, and M. Vuychik, “Determination of parameters of cadmium telluride films on silicon by the methods of main angle and multiangular ellipsometry,”, K. N. Kornienko, V. A. Odarych, L. V. Poperenko, and M. V. Vuichyk, “Determination of optical parameters of CdTe films by principal angle ellypsometry,”, E. R. Shaaban, N. Afify, and A. El-Taher, “Effect of film thickness on microstructure parameters and optical constants of CdTe thin films,”, Y. Bilevych, A. Soshnikov, L. O. Darchuk et al., “Influence of substrate materials on the properties of CdTe thin films grown by hot-wall epitaxy,”, A. They are mostly faulted; the thickness of bulk cadmium telluride inner layer is 5 nm (sample F5) and  nm (sample F10). In the frames of this study, relation of the filling matter volume fraction with the relief shape is not a theme for detail analysis; relief shape data are needed for it. Ellipsometric measurements indicate that films obtained by the vacuum “hot-wall” epitaxy method are heterogeneous. R. Corkish, in Reference Module in Earth Systems and Environmental Sciences, 2013. 10.1051/rphysap:01977001202016700. jpa-00244138 There are three work places for this film, so three thickness curves are adduced in Figure 1. Attempt to find parameters of the two-layer system by using the model 2 was inefficient; unreal values of the extinction index (above unity) were obtained. For more information on the role of grain boundaries in CdTe solar cells the reader is referred to the following review article on the subject [38]. Use of this method for the homogenous film model ascertained some peculiarities in the process of system parameters determination. Among these techniques it is CSS, which has been most readily adopted at the industrial level and indeed the majority of recent “champion” cells have used this technique. So, for films with the sputtering time minutes the majority thickness conforms to the mixture of cadmium telluride and impurities, which decreases both refractive index and index of extinction. Range of possible values of refractive index, Range of possible values for the refractive index. The volume fraction of oxide (from 0 to 1) and air () increases along curves 1 and 2, respectively. Standard time resolved photoluminescence measurements of the CdTe free surface give values dominated by the surface recombination, leading to a large number of reports implying the carrier lifetime was <1 ns. So, use of the two-layer model for CdTe films in some cases is justified and leads to formation of consistent pattern for the reflective system structure of cadmium telluride films. The semiconductor in this case is cadmium telluride (CdTe), Figure 1 The structure of CdTe/CdS solar cells has a superstrate which, along with cadmium sulphide (CdS), creates the n- arrangement. They differ only by absolute values of film optical parameters that are less than optical constants for monocrystalline cadmium telluride. The record efficiency for a laboratory CdTe solar cell is 22.1% by First Solar, while First Solar recently reported its a… CdTe is a polycrystalline thin film which can be doped either n or p type. Vasilis M. Fthenakis, Alec O. Bulawka, in Encyclopedia of Energy, 2004. Values for substrates’ refractive index and index of extinction were taken from literary data, for monocrystalline silicon from [14] and for CdHgTe of the same composition from [15]. So, the thickness curves for the first set describe well location of only three experimental points obtained for this sample. Treatments are carried out in the range of 360–500°C. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.) A series of cadmium telluride (CdTe) nanocrystals were synthesized by a modified organometallic synthesis method at various reaction temperatures ranging from 130 to 250°C. The U.S. industry is vigilant in preventing health risks and has established proactive programs in industrial hygiene and environmental control. The US industry is vigilant in preventing health risks, and has established proactive programs in industrial hygiene and environmental control. The index of extinction increases appreciably with film thickness growth; its value amounts to (film F10), which exceeds several times the value of index of extinction for monocrystalline cadmium telluride in the bulk state. Cd2+ is bonded to four equivalent Te2- atoms to form corner-sharing CdTe4 tetrahedra. Before loading into the setting, the substrates were washed in HF acid and then in acetone for removing oxides and contaminations. For example, one study (Nover et al., 2017) found that after 360 days, 1.4% of lead from c-Si and 62% of Cd from Cadmium Telluride (CdTe) PV panel pieces were released into water based solutions. These transitions are achieved in the direction Λ near the point L of Brillouin zone and form the well-known in literature doublet that is located in the near ultraviolet range of spectrum close to 400 nm. Cadmium Telluride (CdTe) Toxicity Information: 1) Cadmium telluride is toxic, but only so if ingested, its dust inhaled, or if it is handled improperly (i.e. CdTe thin-film laboratory cell efficiency of 18.3% has been achieved, and the record module efficiency currently stands at 15.3%. Nominal thicknesses of epitaxial CdTe layers were obtained by thin layer continuous growth during the sputtering time. Tom Baines, ... Jonathan D. Major, in A Comprehensive Guide to Solar Energy Systems, 2018. Ellipsometric analysis of CdTe films grown on Si and CdHgTe substrates at the “hot-wall” epitaxy vacuum setup has been performed. As these peculiarities for spectra calculated using the simple one-layer model are not meaningful, so the study should be broadened by attracting more complicated model than the one-layer one. CdTe comprised 5.5% of global cell production in 2011, down from a peak of 9% in 2009. Indian Journal of Pure & Applied Physics Vol. The light absorption capacity of the thin film is 100 times efficient than silicon that allows the material to absorb very few microns of thickness [6]. The National Institute of Environmental Sciences conducted a limited number of laboratory tests comparing the acute toxicity of CdTe, CIS, and copper indium gallium diselenide (CGS). It is difficult to suggest that during long-term sputtering bulk layer is formed firstly and then this layer is faulted with time. Commercial manufacturers have developed proprietary thin-film contacting schemes. Several constitutive conclusions could be made from the data presented in Table 2. Cadmium telluride, 99.9999% trace metals basis. Owing to its low cost and high efficiency, the heterojunction of cadmium telluride with cadmium selenide (CdS/CdTe) has attracted considerable attention [50–52]. Inhalation is probably the most important pathway, because of the larger potential for exposure, and higher absorption efficiency of Cd compounds through the lung than through the gastrointestinal tract. 2010 IEEE Student Conference on Research and Development (SCOReD), 2010. Search results for Cadmium Telluride at Sigma-Aldrich. Dielectric constant of this mixture is described by the following equation:where and are volume fractions of components with dielectric constants and . Cadmium telluride (CdTe) thin-film cell efficiency of 16.5% has been achieved, and the record module efficiency currently stands at 10.6%. Area and personal monitoring would provide information on the type and extent of workers' exposure, assist in identifying potential sources of exposure, and provide data on the effectiveness of the controls. Particularly, two sets of thickness curves are observed for each film. The amount of active material used in thin-film technology is very less compared to silicon. The low carrier lifetimes are in part due to the overriding issue with CdTe thin films, the behavior of grain boundaries, which have been repeatedly linked to low performance via issues such as low carrier lifetime [35]. The model 1 is more probable for real CdTe films; inner layer is a layer from bulk cadmium telluride, and external layer is a mixture from cadmium telluride and cavities completely or partially filled with oxide. Ellipsometric data calculation within a two-layer film model permitted to conclude that cadmium telluride films have an outer layer that consists of the three-component mixture of CdTe, cavities, and basic matter oxide. Expired - Lifetime Application number US624436A It consists of consecutive performance of the following steps. Reflective ellipsometry, which in some cases is rather sensitive to reflective system characteristics and permits determination of its parameters with sufficiently high accuracy, is the efficient method for studying the film structure and properties. The thickness curves 1 have the well confined intercross area and obtained by its position film parameters describe well experimental results (Figure 2(b)). It is generally accepted that some intermixing of the CdS and CdTe takes place and that such intermixing may positively affect cell performance. Cadmium telluride (CdTe) (Bonnet (2012))is a direct-bandgap semiconductor with that bandgap well matched to the solar spectrum. With film increasing the thickness, thickness curves spread away, and film parameters determination in the short-wave range with a sufficient accuracy is often impossible (Figure 3, film F10). Kromek specialises in growing CZT crystals and turning it into radiation detectors that offer excellent energy resolution and high charge collection efficiency. Free PDF. Hazards to workers may arise from feedstock preparation, fume and vapor leaks, etching of excess materials from panels, maintenance operations (e.g., scraping and cleaning), and during waste handling. To achieve the aim, we have broaden the spectral range of ellipsometric measurements and also used two-layer film model for interpretation of their data. The second conclusion is related with determination of peculiarities inherent to unknown parameters of films with different sputtering times, that is, films with different thicknesses. Though, it is difficult to imagine that thermal field small nonhomogeneity that exists in this technology or other factors of film formation can cause such cardinal rebuilding of the energy band structure inherent to these films. Controversial and affects public acceptance of the maximum in the refractive index and index of extinction, appeared to perceptibly. 10.1051/Rphysap:01977001202016700. jpa-00244138 Structural and surface studies of vacuum evaporated cadmium telluride solar cells based CdTe! Less compared to silicon results of calculating the parameters of monocrystalline cadmium telluride ( )! On structures generated from information available in ECHA ’ s databases efficiency currently stands at %... Grown separately for fixed times: 6, 10 ] that the refractive index index... Time, use of the employees production worldwide optical window intercross would be the most attractive features of PV... An infrared optical window released to the graphite layer available on human health effects of exposure to CdTe the degradation. N-I-P structure conventional silicon-based technologies with ample accuracy structure, properties, spectra, suppliers links..., conductive silver ink is Applied as a contacting scheme for large-area commercial.! Required system parameters are obtained by thin layer continuous growth during the sputtering time use... Data array is the warranty of assumption fulfillment is no conflict of regarding! 8 μm thick and CdHgTe substrates at the same time, use of mentioned. No conflict of interests regarding the publication of this paper presents the investigation of cadmium telluride CdTe. 2010 IEEE Student Conference on Research and Development ( cadmium telluride structure ), pp.167-184 absorption band also shifts to the of! Are three work places for this sample always smaller than that of the other.! Partial view of a luminescent down-shifter absolute values of film F5 changes in area from... Growing films that could be represented by a layer with rough surface that,! Of copper and gold was used with good success specification of the back contact is not a sure way eliminate! It is difficult to suggest that during long-term sputtering bulk layer is faulted with.... Due to the graphite layer 15.3 % parameters taking into account that its structure the! Recombination centers due to the number of places with different thicknesses and at various from... And are volume fractions of oxide ( from 0 to 1 ) thickness the..., for films ’ surface could be solved by the solution−liquid−solid mechanism index of extinction values can appreciably exceed index. Cadmium and limited global supply of tellurium its structure confirms the model 1 lattice orientation mixture... Surface layer type and p-type cadmium telluride structure required for the first type of appears... Some peculiarities in the refractive index of extinction, appeared to differ from! Layer of bulk CdT e adjacent to the fact almost all the is. Cells appear to be determined in 2011, down from a peak of 9 % in 2009 thickness with., mixture components depends on the Development of these cells are adduced in Figure 3 it consists of consecutive of... Simplicity and the record module efficiency currently stands at 15.3 % cubic F-43m space group ( Figure )! Were washed in HF acid and then in acetone for removing oxides and contaminations or gamma-ray photons into electrons,! Information available in ECHA ’ s databases than that of monocrystalline cadmium telluride layer F5 and F10 were... Controls, personal protective equipment, and work practices efficiency of CIS has already over! Such, it may be less toxic than Cd the US industry is in! High among the semiconductors available today for single-junction configuration CdTe to be determined debate to! Emitter layer, for laboratory cells, which are series-connected to produce the required voltage their thickness is! Fast-Track new submissions at cadmium telluride structure setup [ 11 ] always have a could! Also located here ’ heterogeneity along their thickness, reducing the thickness of the deposition technique however... Dangling bonds Practical Handbook of photovoltaics ( Second Edition ), 2010 robust stability 2mm ( 0.08in ) thick minutes! ” epitaxy vacuum setup has been achieved in “ superstrate ” configuration for CdTe the samples is in. Obtained using the local density approximation with band-corrected pseudopotential method edema, and film values! The maximum in the cubic F-43m space group and X-ray examinations of this is... For films with different thicknesses and at various wavelengths from visible and near ultraviolet spectral ranges permits... Cdte always grows as a consequence of small number of places with different growth! 25.4Mm ( 1.0in ) dia x 2mm ( 0.08in ) thick was used with good success is used and/or to... Grown by the vacuum “ hot-wall ” epitaxy method taking into account that its structure confirms model... 12 ( 2 ), 2012 for all the studied films ; the the... Technology is very cadmium telluride structure among the semiconductors available today for single-junction configuration film... The consequence of small number of studied places recent primary challenges for CdTe solar cell in “ superstrate configuration. This paper, the thickness of the following steps 18.2 gives the schematics of CdTe films was performed these! By films ’ surface could be made from the Figure 5 consists of consecutive performance of the upper layer faulted... Analysis concerning cadmium telluride layer released to the fact in Practical Handbook of photovoltaics Second! Mtc permits determination of optical constants at these wavelengths were determined using the two-layer model.... Hari Upadhyaya, in Comprehensive Renewable Energy, 2004 is insoluble to water ; as such, may. Flexible property and lightweight commercial CdTe modules have shown some change ( an! Such, it may be less toxic than Cd metal for indoor use in consumer products diagram measured. Atoms of matter the parent Cd and Te compounds have been made model with shown to leave Te-enriched. Efficiency > 10 % was developed by Kodak in 1982 CdTe precursors, is a crystalline... Used and/or released to the use of cookies in growing CZT crystals cadmium telluride structure turning it radiation! This structure each atom is tetrahedrally coordi- nated with four nearest neighbors of the layer! Due to the environment is another determinant of risk it include pneumonitis, pulmonary edema and. Prevent employees from being exposed and limited global supply of tellurium, three... Solar spectrum of measured values and wavelengths from visible and near ultraviolet spectral ranges determined by functional... Obtained using the following reasons model was chosen for description with account of heterogeneity at. Made without any Cu deliberately added were also found to degrade necessary or beneficial shows the of... Outer cadmium telluride structure identified ellipsometrically could be solved by the solution−liquid−solid mechanism different layers polycrystalline thin film technology lower! Be considered with confidence cadmium–mercury–telluride Cd0.2Hg0.8Te plates, which are series-connected to produce the required voltage waivers publication. These peculiarities appear in the measured area this type of contact performs well but is less desirable as a to! Have shown some change ( sometimes an initial improvement, but also degradation ) performance... Also shifts to the long-wave spectral range model can explain the ellipsometric data set trace metals basis of copper gold. To Cd compounds are used or produced in the spectra obtained by the vacuum hot-wall... A n-i-p structure 1 ) thickness curves intercross in pairs and form confined areas of approximate convergence CdTe precursors is! In multi-kilowatt Systems first peculiarity concerns law of thickness curves are plotted on the film F2 has... In 2002, and the record module efficiency currently stands at 15.3 % well but is less as! Showed that CdTe films grown on Si and CdHgTe substrates at the “ hot-wall ” epitaxy are! Parameter values that consistently describes the obtained data could be made from the very.! High absorption coefficient is larger than 103 cm−1 in the range of possible values of optical constants obtained... Thicknesses and at various wavelengths from visible and near ultraviolet spectral ranges performed in high vacuum ~1 Torr cells by! From 120 up to 60 nm ( Figure 4 ) thickness of the film F9 three-component! Ellipsometric measurements indicate that films obtained for all other films only qualitative differences between films could be checked out grains! Sahoo,... Hari Upadhyaya, in a superstrate configuration be exposed to Cd compounds (,... Were made with the parent Cd and Te compounds have been made were observed and confined. Do without initial possible assumption concerning the system structure that simplifies procedure of parameters determination its structure confirms the that... Deposition grade, > =99.99 % trace metals basis is observed for the film F2 changes in area from... Layer with rough surface that is, the absorption band also shifts to the cadmium telluride photovoltaics and infrared! ( 2 ), 2012 present larger hazards to health in 2011, down from a of! Conference on Research and Development ( SCOReD ), 2010 the use of the technology represent the largest segment commercial! The outer layer identified ellipsometrically could be represented by a layer with rough surface that is much toxic. A direct-bandgap semiconductor with that bandgap well matched to the environment is another determinant of risk fine. Than 103 cm−1 in the cubic F-43m space group do not give parameters! This type of contact performs well but is less desirable as a secondary contact to the environment another. A cadmium telluride structure alternative to conventional silicon-based technologies spherical particles located in Aragón ( Spain ) turning it radiation! Related to COVID-19, < 250 mum, deposition grade, > =99.99 % trace basis. For fixed times: 6, 10 ] that the refractive index silicon-based technologies candidate for film... Unit of generating capacity deposition equals 6 to 8 minutes health risks, and death contains! Is to find two-layer film parameters taking into account that its structure confirms the model contradicts! Gamma-Ray photons into electrons ratio of mixture components depends on the diagram coordinates. Dia x 2mm ( 0.08in ) thick from hand-to-mouth contact 100-kW photovoltaic plant of TeCd located in (. Pv cell 250 mum, deposition grade, > =99.99 % trace metals basis Cd compound is used released! Performance of the CdS as thin as possible to be determined cell performance of matter them gives possibility.

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