Photovoltaics cadmium telluride

Commonly used II-VI compounds include zinc sulfide, zinc selenide, zinc telluride, cadmium sulfide, cadmium telluride, and mercury cadmium telluride. These materials are not as widely used as the III-V compounds, one reason being that it is difficult to achieve p-type doping. Mercury cadmium telluride is used extensively in military night sights, which detect in the 8-13 im spectral band (a similar material, platinum silicide, is being developed for that purpose). The major applications ofCVD II-VI compounds are found in photovoltaic and electroluminescent displays. 

W.F.H. Micklethwaite, The Crystal Growth of Cadmium Mercury Telluride Paul E. Petersen, Auger Recombination in Mercury Cadmium Telluride R.M. Broudy and V.J. Mazurczyck, (HgCd)Te Photoconductive Detectors M.B. Reine, A.K. Sood, and T.J. Tredwell, Photovoltaic Infrared Detectors M.A. Kinch, Metal-Insulator-Semiconductor Infrared Detectors... 

A number of companies are currently involved in thin-fllm photovoltaics [17], and low-cost multilayer thin-fllm amorphous silicon and CdTe (cadmium telluride) systems have already been installed in large numbers with efficiencies of the order of 10% and of about 80% output after 25 years of operation. Large-scale plants have been announced for the so-called CIS (cadmium indium selenide) and CGIS (copper gallium indium diselenide), technologies with production efficiencies in the range 12-13% and laboratory measurements up to 19.9% [18]. 

A photoconductive detector is a semiconductor whose conductivity increases when infrared radiation excites electrons from the valence band to the conduction band. Photovoltaic detectors contain pn junctions, across which an electric field exists. Absorption of infrared radiation creates electrons and holes, which are attracted to opposite sides of the junction and which change the voltage across the junction. Mercury cadmium telluride (Hg,. Cd/Te, 0 < x < 1) is a detector material whose sensitivity to different wavelengths is affected by the stoichiome-try coefficient, x. Photoconductive and photovoltaic devices can be cooled to 77 K (liquid nitrogen temperature) to reduce thermal electric noise by more than an order of magnitude. 

An imager having an element packing density of 90% is disclosed in US-A-4104674. Infrared photovoltaic detectors of mercury cadmium telluride are mounted on a silicon substrate. Electrical contacts are made by thin-film metallizations. 

The imager comprises a silicon substrate 1 in which a read-out circuit such as a CCD is integrated. The read-out circuit has input regions 2 and metal electrodes 3. An array of photovoltaic detector elements 10 are formed in a p-type mercury cadmium telluride body 11 which is mounted by an insulating adhesive 21 on the substrate. Each detector element... 

Cadmium telluride — A II—IV compound -> semiconductor frequently employed in infrared systems (active component in infrared detectors) and -> photovoltaic devices. Electrochemical - passivation has been employed to improve surface recombination behavior. 

McCandless, B.E. Sites, J.R. Cadmium telluride solar cells. In Handbook of Photovoltaic Science and Engineering Luque, A., Hegedus, S., Eds. Wiley Chichester, 2003 617-662. 

Photovoltaic Device - A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semi-conductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multi-crystalline, or amorphous forms. 

Photovoltaic cells, or solar cells, work by containing matericadmium telluride, or copper indium selenide whose electrons, ire easily excited by photons from the sun, creating electricity. 

Theoretical conversion efficiencies of photovoltaic systems depend on the semiconductor materials used in the cells and on the ambient tanperatuie. The materials currently used to make photovoltaic cells can be grouped into three broad categories 1) expensive, efficient monocrystalline silicon, 2) less efficient but much lower cost polycrystalline silicon, and 3) the lowest cost and poorest performer, amorphous silicon material. Conversion efficiencies of commercial polycrystaUine silicon cells are 10 to 15 percent. Now the primary development areas are in how to use monocrystalline silicon with solar concentrators and making thin-film cells by depositing a 5- to 20-micron film of silicon onto an inexpensive substrate, because the estimated efficiency of these cells is above 20 percent. Work is ongoing with other materials, including amorphous silicon (a-Si), copper indium diselenide (CuInSe2 or CIS) and related materials, and cadmium telluride (CdTe). 

Photovoltaic (PV) Cell Semiconducting material, such as crystalline silicon or cadmium telluride, that converts solar radiation into direct current electricity using the photoelectric effect. 

The most common detectors found in commercial infrared spectrometers are sensitive in the mid-infrared region. An example is the mercury-cadmium-telluride (MCT) detector, a photovoltaic device for which the potential difference changes on exposure to infrared radiation. 

Ottova et al. looked at two-compartment semiconductor-septum electrochemical photovoltaic cells with cadmium selenide and cadmium selenide telluride for water photolysis [126], They used cells consisting of two chambers separated by a CdSe or CdSe/CdTe bipolar electrode. The bipolar electrodes were prepared by painting a CdSe slurry on a metal substrate or by ultrasound-aided electrodeposition from CdSe solution in ZnCl2. The photoresponse (voltage and current output) and hydrogen yield from photo-induced electrolysis of H20 in the dark chamber of the cell were evaluated as a function of CdSe preparation method. The ultrasound-aided deposition technique gave excellent coatings of CdSe. 

There is a problem with the widespread use of arsenic, cadmium, and selenium in electronic and photovoltaic devices. Cadmium mercury telluride is used in infrared-sensing night goggles. Cadmium sulfide, cadmium selenide, gallium arsenide, and analogues, are used in solar cells. If their use becomes widespread, then an efficient system of collecting used cells for reprocessing will be needed. Some workers feel that it will be better to use nontoxic silicon cells wherever possible. (Solar cells are discussed in Chap. 15.)... 

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