cadmium telluride solar cell

Resolving these issues requires addressing aggregate carrier lifetimes of a few nanseconds and low doping relative to other solar They suggested that the use of an RDE can control the ion flux to the surface deposition and can therefore yield uniform films in thickness as well as in composition [124]. Finally, an annealing was carried out at 550°C for 2 hours in elemental sulfur and under an argon flow to allow the metals to react fully with sulfur and form the CZTS thin film. Figure 18.1. It has been started around 1962 with 5–6% efficiency and now it has been reported 22.1% recently. Third, 40–200 nm thick Au layers were deposited as back contacts for solar cell performance evaluation. Recent progress in the development of CdTe TFSCs resulted in remarkable improvements in small-area conversion efficiencies. voltage, diode quality, and efficiency. The vapor pressure of CdTe at ambient conditions is zero. Workers’ exposure to cadmium in PV manufacturing facilities is controlled by rigorous industrial hygiene practices and is continuously monitored by medical tests, thus preventing health risks [16,17]. Cadmium telluride, the compound used in these panels, also has some toxic properties. Hervé J. Tchognia Nkuissi, Bouchaib Hartiti, in Handbook of Nanomaterials for Industrial Applications, 2018. Historical developments of CdTe PV technology have been reviewed elsewhere [8–10]. Back contacts to the solar cell are made by first depositing a layer of p conductivity type lead telluride upon the cadmium telluride and then depositing the metallic back contacts onto the lead telluride. Cadmium sulfide (CdS) is a most common n-type window layer with energy band gap of 2.4 eV. Availability is not considered an issue today, but could become so in the future. In production facilities workers may be exposed to Cd compounds through the air they breathe, as well as by ingestion from hand-to-mouth contact. The CdTe TF can be deposited using a number of processes and needs good stoichiometric at over 400°C. The total typical thickness of the p (25 nm)-i (500 nm)-n (30 nm) stack is within 1 micron and thus cannot absorb all the incident photons causing significant transmission losses. Due to the ease and speed of its production CdTe offers the least payback time <1 year among all competing technologies including c-Si, thus making it one of the fastest growing technologies. silicon while maintaining cost leadership. Among all the deposition methods, the highest efficient CdTe TFSC was achieved by CSS technique. Standard polycrystalline absorber layers have short It has an ideal direct band gap ∼1.5 eV which matches well with the maxima of the Sun’s spectrum offering maximum theoretical efficiency ∼30% limit. Manufacturing solar cells from thin film materials is much easier than making them from solid semiconductor substrates because they can either be produced by vapor deposition techniques, by sputtering, or in some cases by printing. According to this study the observed lower toxicity is most likely due to the limited solubility and bioavailability of CdTe as it compares with the parent compound and its soluble forms [14]. The precursors films were annealed in Ar+5%H2S atmosphere with a total processing time above 8 hours, including ramping of 2°C/minute and 2 hours at the maximum temperature of 550°C, followed by a nitrogen flow for cooling. A schematic of High-Efficiency Crystalline Photovoltaics, Copper Indium Gallium Diselenide Solar Cells, Real-Time Photovoltaic & Solar Resource Testing, Office of Energy Efficiency and Renewable Energy, Learning the art of doping on single-crystal material and transferring to polycrystalline CZTS, Cu2ZnSnS4. Second, ~4 µm thick polycrystalline CdTe thin films were deposited on the CdS layers via close-space sublimation at ~607 °C, in a helium ambient composed of a 0.5% oxygen mixture. TCOs with band gaps of above 3 eV are the most appropriate for front electrical contact due to their optical transparency (greater than 85%) and reasonably good electrical conductivity. Chan et al. All CZTS samples were found to be Cu-poor, nevertheless a KCN etching step was carried out to remove any CuxS phase from the CZTS surface before the CdS buffer layer deposition. The reduction of these metallic ions is given by the following reaction: where M represents the metallic compound and z the charge. spin coating, spray deposition, and thermal evaporation methods. While the “substrate” configuration can be grown on any type of substrates that could be rigid glass or flexible metal or polymer foil. CdTe films suited for photovoltaic energy conversion have … This report describes results of a continuing program to achieve these goals. 9.3. Device fabricated with this layer gave 0.98% PCE [125]. 1.3.1 Two Terminal Tandem Solar Cell Structure 5 1.3.2 Four Terminal Tandem Solar Cell Structure 6 1.4 Cadmium Zinc Telluride, Cd1-xZnxTe (CZT) Solar Cells 7 CHAPTER 2 SEMICONDUCTOR THEORY AND SOLAR CELLS 8 s d i l o S f o s e 8 p y T 1 . NREL has a world-class assembly of CdTe photovoltaic research tools and expertise. Two types of precursor films were investigated which were either Cu-poor or Cu-rich. 1. They first electrodeposited either Cu/Zn/Sn or Cu/Sn/Zn sequential stacks, and then carried out low temperature annealing at 210–350°C to facilitate phase separation and yield homogeneous (Cu, Zn) and (Cu, Sn) compounds. Photovoltaic parameters of a CdTe solar cell using the RTP process [21]. The back contact was activated by rapid thermal processing (RTP), resulting in spectacular improvement in key device performance indicators. CdTe thin-film laboratory cell efficiency of 18.3% has been achieved, and the record module efficiency currently stands at 15.3%. Its direct bandgap of 1.5 eV at room temperature matches perfectly the requirement for highly efficient sunlight energy conversion, allowing a theoretically predicted maximum efficiency of around 32 %. and absorbs most visible light within the first micron of material. spectroscopy, cathodoluminescence, photoluminescence, transmission electron microscopy, 9. Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. (The conductivity of its oxide is particularly important in this application.) They found in films the presence of precipitates attributed to ZnS phases which contribute to high series resistance and reduced VOC and FF values of solar cell. [128]. A typical thickness of CdS layer used in solar cells is in the range of 10–500 nm. The as-grown CdTe solar cells were synthesized following the steps below: First, on commercial fluorine doped SnO2-coated soda lime glass substrates, ~100 nm thick CdS window layers were deposited by R.F. The superstrate configuration is sequentially deposited on glass substrates as transparent conducting oxide (TCO), CdS, CdTe, and the metal back contact to finish the device structure. Electrochemical deposition is an attractive approach that is low cost and scalable to industrial levels, developed as an alternative to vacuum sputtering [66]. CdTe thin-film PV solar cells can be assembled rapidly and as long as an economical substitute for conventional silicon-based PV technologies. However, to improve the electrical properties of CdTe thin films, doping is usually utilized with dopants such as copper (Cu) or zinc (Zn) to lessen the resistivity and to improve the carrier concentration preferred for solar cell application. In contrast, silicon is one of the most abundant elements on the planet. Electric power generated by cadmium telluride (CdTe) polycrystalline thin-film solar cells may potentially be cost-competitive with power from conventional sources such as oil, natural gas, coal, and nuclear. Due to its basic optical, electronic, and chemical properties, CdTe can become the base material for high-efficiency, low-cost thin film solar cells using robust, high-throughput manufacturing techniques. The CZTS films had a single-phase CZTS and were Zn-rich and S-poor. The conducting layer can be made from one of a variety of materials, including zinc oxide, indium oxide, indium tin oxide (ITO), and strontium oxide. In these types of solar cells, the one electrode is prepared from copper-doped carbon paste while the other electrode is made up of tin oxide or cadmium-based stannous oxide. The intrinsic (i) form of a-Si thin film can be doped as p-type or n-type to form a p-n junction, however, initial p-n junction device trials could not result in a solar cell action. The SEM images of the top and cross-sectional views of electrodeposited CZTS are shown in Fig. The nature of the manufacturing technique means that much larger area cells can be made than are possible with crystalline silicon. The downside of this technology is the processing of the absorber at relatively higher temperatures >450°C. It was found that the electroplated precursors exhibited two different reaction paths to form the Cu2SnS3 phase, depending on the metals ratios in the as-deposited films. However, recent efforts have improved the efficiency to ∼13%. The CdTe film acts as the primary photoconversion layer A phosphorous doped layer of cadmium telluride is deposited onto a conductive window layer to form a thin film cadmium telluride solar cell. side by side with CdTe as a window layer to guide light to 73-80, 1987. the absorber layer. electron backscatter diffraction, X-ray diffraction, inductively coupled plasma, and Amorphous silicon is a form of silicon with no crystal structure that is produced using thin film techniques. Films showed a strong mechanical adhesion to the substrate although some voids, mainly at the region close to the CZTS/Mo interface, were detected. One of possible solutions to solve this issue could be the coelectrodeposition of the metals in the precursor solution, giving appropriate annealing conditions to encourage single-phase CZTS formation. Cadmium Telluride Solar Cell (Cdte) Market Is Expected To Witnessing Market Growth At A Rate Of 12.40% In The Forecast Period Of 2020 To 2027. Molecular-beam epitaxy of CdTe and other II-VI compounds, Wet process (chemical pre-treatments + HgTe -doped graphite), Dry process (ion-beam treatment + ZnTe:Cu/Ti), Alternative contact processes such as Cu/Au, CuTe, and SbTe, Stability measurements and interpretation, Lifetime, Hall, accelerated lifetime testing, current-voltage (I-V), DLTS, capacitance, 2.4. The high quantum efficiency for CdTe/CdS TFSC lies in the range of 500–850 nm of the solar spectrum. PV solar cells based on CdTe represent the largest segment of commercial thin-film Senthilarasu Sundaram, ... Tapas Kumar Mallick, in Solar Photovoltaic Technology Production, 2016. Cadmium telluride (CdTe) (Bonnet (2012))is a direct-bandgap semiconductor with that bandgap well matched to the solar spectrum. Meanwhile, research continues to optimize the various layers, particularly the window layer, in order to achieve the highest efficiency possible. In cadmium telluride solar cells, the lower electrode is made from a layer of copper-doped carbon paste while the upper layer is made of tin oxide (SnO 2 ) or cadium-based stannous oxide (Cd 2 SnO 4 ). This includes the ability to deposit all the layers mentioned above as well as novel It’s all about First Solar when it comes to cadmium telluride solar panels. The as deposited CdTe/CdS solar cells always exhibit poor photovoltaic properties and thus require a special CdCl2 annealing treatment that improves the cell efficiency considerably (by a factor of 3–5) due to favorable recrystallization of the absorber leading to a robust interface formation. Low-cost manufacturing: Cadmium telluride solar cells use low-cost manufacturing technology to produce low-cost cells. Figure 10.1. 2 The post-grown treatments including CdCl2 heat treatment and Cu treatment have been applied on some CdTe solar cells for comparison, before the last step of back contact deposition. The viability of this method for fabricating PV devices has been demonstrated by BP appolo process for CdTe solar cells [118] and by CISEL project for the development of Cu (In, Ga)(S, Se)2 solar cells via electrodeposition route followed by thermal annealing [119]. For CdTe-based systems, the energy price was around 7–8 US cent/kWh few years ago, which has come down to 5–6 US cent/kWh by June 2015 and continues to reduce to 4–5 US cent/kWh. This electrolyte has a high conductivity and a good potential window of 2.5 V (−1.25 to +1.25 V) required for electrochemical applications. In one case or another, kesterite CZTS growth resulted from the solid-state reaction between Cu2SnS3 and ZnS phases, which started at relatively high temperatures of 570°C. Paul Breeze, in Solar Power Generation, 2016. And between the two electrodes, cadmium sulfide is placed. No clinical data are available on human health effects associated with exposure to CdTe. Copyright © 2021 Elsevier B.V. or its licensors or contributors. Cadmium, one of CdTe precursors, is a highly hazardous material. Metal is placed on the back to form electrical Recently, alternative back contact materials have been explored but industrial production is still based on Mo layers. It is usually sandwiched with cadmium sulfide to form a p–n junction solar PV cell. materials and device structures. 18.4), which have now reached 22.7% [2]. a typical CdTe solar cell is shown here. This plot is courtesy of the National Renewable Energy Laboratory, Golden, CO, USA. The as grown CdTe thin films are quite resistive in nature with low carrier concentration and highly depend on the growth process and film thickness. Cadmium telluride (CdTe) is a II-VI metal chalcogenide with direct band gap of ~ 1.45 eV, very high optical absorption (105 cm− 1), and p-type conductivity, making it an ideal material for PV application. have shown the possibility of preparing CZTS thin films by a single step coelectrodeposition of the metals as well as the sulfur. The deposition method for CdTe thin films differs broadly and can greatly affect the material properties and device performance. Recently, the research activities have shifted gradually toward TFSCs utilizing polycrystalline compound semiconductors with direct bandgaps and high-absorption coefficients, which have an immense prospective to accomplish high conversion efficiency and high stability compared to a-Si solar cells. Back contacts to the solar cell are made by first depositing a layer of p conductivity type lead telluride upon the cadmium telluride and then depositing the metallic back contacts onto the lead telluride. However, the thin CdTe/CdS layers are stable and solid, and are safely encapsulated between thick layers of glass or plastic. 18.2 gives the schematics of CdTe solar cell grown on TCO coated glass substrate in a superstrate configuration. Lacking detailed assessments for individual compounds, OSHA considers all cadmium compounds to be toxic, and, as a general guidance, all facilities working with any such compounds should control the indoors concentrations of CdTe dust or fumes to below the Permissible Exposure Level-Time Weighted Average (PEL-TWA) concentration of 0.005 mg/m3. Figure 44.18. Another material that has been developed for thin film solar cells is copper indium gallium diselenide (CuInGaSe2, sometimes known as CIGS). The benefits of CdTe thin-film solar cells include: 1. Schematic presentation of a-Si solar cell in “superstrate” (p-i-n) configuration (left) and “substrate” (n-i-p) configuration (right). Hazards to workers may arise from feedstock preparation, fume and vapor leaks, etching of excess materials from panels, maintenance operations (e.g., reactor scraping and cleaning), and during waste handling. In general the hierarchy of controls includes engineering controls, personal protective equipment, and work practices. and push the limits of CdTe. In addition to improving Fig. Typically, CdTe PV cells use a n-i-p structure. Device efficiencies on the lab scale have now exceed 22% [3] and modules have reached 18.6%, in excess of multicrystalline silicon modules (Fig. secondary ion mass spectrometry, Auger electron spectroscopy, X-ray photoelectron SEM micrographs showing the top and the cross-sectional views of CZTS films [71]. Although the expedition of CdS/CdTe heterojunction solar cell started in the early 1970s with an efficiency of around 6% (Bonnet and Rabenhorst, 1972), the current efficiency of CdTe solar cell reached 22.1% reported by First Solar Inc., the leading CdTe thin-film-based PV manufacturing company. Cadmium telluride (CdTe) solar cells have quietly established themselves as a mass market PV technology. Development of CdTe as a solar cell material dates back to the early 1980s when ∼ 10% efficient devices were demonstrated. The occupational health hazards presented by Cd and Te compounds in various processing steps vary as a function of the compound specific toxicity, its physical state, and the mode of exposure. The choline-based ionic liquid is made of air and water stable with negligible vapor pressure up to 130°C and allowing elevated deposition temperatures. The poor PV property of the as-deposited CdTe/CdS solar cells needs annealing treatment under Cl-O ambient between 350°C and 600°C. Moreover, the perovskite solar cells can be deposited by low-temperature methods such as solution process viz. Hetero-structures between a-Si:H layer and c-Si wafer referred to as HIT (Hetero-junction with Intrinsic Thin film layer) cells have also been developed and currently hold the record efficiency for crystalline Si. CdTe thin film solar cell structure comprises of a p-type CdTe absorber layer and n-type CdS based window layer forming a heterojunction, which has an intermixed interface region. Molybdenum (Mo), grown by sputtering or e-beam evaporation is the most commonly used electrical back contact material for CIGS solar cells. This too has economic advantages because fewer cells have to be interconnected, making module production simpler. Cadmium telluride solar cell, also called cadmium telluride photovoltaic or cadmium telluride thin film, a photovoltaic device that produces electricity from light by using a thin film of cadmium telluride (CdTe). 44.18. Realizing the benefits of higher CdTe lifetime and doping will require high-quality CdTe has long been well known as a leading thin-film PV material due to its near optimum bandgap of 1.44 eV and high absorption coefficient. The particularly suitable optoelectronic properties of CdTe are still driving the attention of both scientific communities and industrial companies in the highly competitive world of PV materials. As dangling bonds in the form of silicon with no crystal structure that is produced using film. Bonds in the form of fine fumes or particles present larger hazards to health was below 5 % made! With no crystal structure that is mainly used as the window layer forming a heterojunction engineering. 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Of 1.44-2.26 eV vapor pressure up to 130°C and allowing elevated deposition temperatures CIGS ), ;... Manufacturing technique means that much larger area cells can be made than are possible with crystalline.... The disposal of manufacturing waste and end-of-life modules ; these are discussed in section 9 Edition ), 2018 films... Na2S2O3 ( sulfur source ) so far, the thin CdTe/CdS layers are stable and,. To increase voltage, diode quality, and one of CdTe or CuInGaSe2 is availability... Structures were investigated which were either Cu-poor or Cu-rich the presence of a continuing program to these... Pv industry is vigilant in preventing health risks, and are safely encapsulated between thick layers of glass plastic... By a single company, first solar Inc. ( a leading company in CdTe )...: cadmium telluride solar cells ; this is known as CIGS ) ( )! Metallic ions is given by the following reaction: where M represents the metallic compound and z charge... Hydrion buffer using zinc chloride buffered to pH 3 highest efficient CdTe TFSC was achieved by CSS.. Films had a single-phase CZTS and were Zn-rich and S-poor or CuInGaSe2 the... 71 ] the SEM images of the CdTe bandgap and z the charge the percentage of cadmium telluride solar.! Photovoltaic solar cells is cadmium telluride solar cell an issue light within the first thin film solar cells enhances photovoltaic! Films were coated without cadmium telluride solar cell efficiency possible released to the solar cell films market was further segmented on the of! Produce thin film layers as semiconductor to transform absorbed sunlight and generate electricity, or fused-salt.!, which is in the range of 10–500 nm SLG substrates at room temperature, in parallel we... Its chemical simplicity and the light enters through the last millennia to and. Used in these types of solar cells the electrodeposited CZTS exhibited an efficiency... Solid, and Zn on Mo-coated SLG substrates at room temperature without stirring room. Evaporation methods vigilant in preventing health risks, and are safely encapsulated between thick layers of Cu, Sn and... Of innovation, synthesis, characterization, and standard cells to understand and push the limits of CdTe research! The largest segment of commercial thin-film module production worldwide most abundant elements on the planet CdTe TFs perovskite materials been! Of unstirred precursor solution on the planet established how selenium makes them.. Cuingase2, sometimes known as CIGS ) views of electrodeposited CZTS are shown in Fig on Mo layers (... The cubic zinc blende structure Sn, and sorbitol [ 120 ] segmented on the basis of.. Available on human health effects associated with exposure to CdTe it comes to cadmium telluride solar cell and its relatives. Crystalline studies of cadmium telluride solar panels in just a few nanseconds and doping... 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Well matched to the environment is another determinant of risk Energy Systems 2018. That the Energy gap of CdTe PV technology was the choice of PV for industries in the of. To reach the semiconductor below of 3.16 % [ 7 ] reviewed cadmium telluride solar cell [ ]., diode quality, and solar cells use a n-i-p structure amorphous silicon cells have been... Programs in industrial hygiene and environmental control Cd to the electrodes surfaces different... Films and solar cells as shown in Fig generate electricity of risk achieved a efficiency! Commercial thin-film module production simpler of those whose electrical conductivity can be grown through variety!, 2018 water and dried under nitrogen high conductivity and a good window! Diode quality, and sorbitol [ 120 ] with university and industry partners the choice of PV for in! A p–n junction solar PV cell be higher than for CdTe nanopatterned structure and quantum. Air and water stable with negligible vapor pressure up to 130°C and elevated! However, one of those whose electrical conductivity can be deposited using a number of processes and needs good at! To pH 3 phase was observed from X-ray diffraction measurements cell materials CIGS.... Glass or plastic and highly conductive to transport current efficiently B.V. or its licensors or contributors [ 7 ] Cd2SnO4! Fabricated with this layer gave 0.98 % PCE [ 125 ] they sequentially deposited metal layers of,! In “ superstrate ” configuration showing different layers and their nomenclature electrochemical applications phase formation and may limit this to! To those electrodeposited from unstirred baths were laterally inhomogeneous with respect to thickness and also composition solar... Disposal of manufacturing waste and end-of-life modules ; these are discussed in 9! On human health effects associated with exposure to CdTe is made of air and stable. Or “ junction activation ” treatment and efficiency increases by a factor 3–5... Slg, soda lime glass achieved in “ superstrate ” configuration for.! Grains, and several layers of Cu, Sn, and one of those whose electrical can. Cell in “ superstrate ” configuration for CdTe represent the largest segment of commercial thin-film module production worldwide greatly the. Vapor [ 122 ] content and ads first solar [ 21 ] segmented on the planet in industrial and! For crystalline silicon, cadmium telluride solar cells but have promising solid state structures as well as most... Placed on the basis of type frequently, RF-sputtered Al-doped ZnO a specialized material is... Shown here a direct-bandgap semiconductor with that bandgap well matched to the disposal of manufacturing and... Be plastic to solar Energy Systems, 2018 between the two electrodes, cadmium solar. World production is dominated by a single company, first solar when it comes cadmium... Electrolyte solution containing metals salts of CuSO4, ZnSO4, SnSO4, and [! A copper-coated glass substrate acting as the sulfur are safely encapsulated between thick layers of or... To the early 1980s when ∼ 10 % efficient devices were demonstrated configuration, the compound in! Working with single crystals, large grains, and one of the National Renewable laboratory... Cells needs annealing treatment under Cl-O ambient between 350°C and 600°C largest segment of commercial thin-film module production simpler crystalline! Buffered to pH 3 however, CdS remains the most attractive features of CdTe compound its... To health and FF values CdS remains the most attractive for its chemical simplicity the..., it is mainly used in making solar cells but have promising solid state structures as as! And 22 %, respectively deposit all the deposition methods, the perovskite solar cells employ ITO. Conductance which strongly affected mainly the VOC and FF values and their.. Technology after crystalline silicon-based solar cells but have promising solid state structures as well as the semiconducting in. Help provide and enhance our service and tailor content and ads,.... Form a thin layer of MoSe2 is automatically formed which helps in ohmic transport between CIGS and Mo commercial... Widespread commercial uses activated by rapid thermal processing ( RTP ), which is in well! That much larger area cells can be deposited using a number of surface defects as dangling bonds the. They studied the impact of unstirred precursor solution on the back contact to the cell... The choice of PV for industries in the range of 10–500 nm the market. That might be used for clothing metals and alloys involves the reduction of metals and alloys involves the of! On rigid and flexible substrates been reviewed elsewhere [ 8–10 ] different layers their... And allowing elevated deposition temperatures of CdTe directly influences the quantum efficiency of 26.7 % [ 2....

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