Cadmium telluride, electrical

Commercially available PV systems most often include modules made from single-crystal or poly-ciystalline silicon or from thin layers of amoiphous (non-crystalline) silicon. The thin-filni modules use considerably less semiconductor material but have lower efficiencies for converting sunlight to direct-current electricity. Cells and modules made from other thin-filni PV materials such as coppcr-indiuni-diselenide and cadmium telluride are under active development and are beginning to enter the market. 

Elhs AB, Kaiser SW, Wrighton MS (1976) Optical to electrical energy conversion Cadmium telluride-based photoelectrochemical cells employing telluride/ditelluride electrolytes. J Am Chem Soc 98 6418-6420... 

J. Brice and P. Capper, eds., Properties of Mercury Cadmium Telluride, Institution of Electrical Engineers (INSPEC), London, 1987. 

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. 

Another exciting thin-film company is FirstSolar (www.firstsolar.com). First Solar claimed to achieve a manufacturing cost of only 1.08 per watt during the third quarter of 2008. The company uses cadmium telluride as a semiconducting material, which is a byproduct of the mining and production of base metals such as zinc and copper. First Solar has entered into many excellent long-term sales agreements with major electric utility companies. 

The next step is to provide electrical connections 3 between the electrode leads 13 and the contact pads 23. Because the active regions are present adjacent the passivated lower surface during the heat treatments, for example when the adhesive layer 4 is cured, they do not suffer significantly from degradation of the material properties of the mercury cadmium telluride... 

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. 

A plurality of thin film field effect transistors 11 are deposited onto a substrate 12. Each of the transistors has a source electrode 13, a drain electrode 14 and a gate electrode 15. Source lines 17 link the source electrodes in each row of the transistors and drain lines 18 link the drain electrodes in each column of the transistors. The source lines and drain lines are electrically isolated by a planarization layer 19. A mercury cadmium telluride layer 20 is deposited onto the planarization layer followed by a top electrode layer 23. The gate electrodes are connected with the mercury cadmium telluride layer by connectors 21. A cross-section of the imager is shown below. 

A silicon substrate 1 comprises a read-out circuit with input regions 2 and metal electodes 3. Detector elements 10 are formed in a p-type mercury cadmium telluride body 11 which is glued to the silicon substrate. Each detector element comprises an n-type region 13. Apertures 20 extend through the mercury cadmium telluride body. The n-type regions 13 are electrically connected to the metal electrodes 3 by a metallization layer 23 formed in the apertures. 

J John Brice and Peter Capper, "Properties of Mercury Cadmium Telluride , 1NSPEC (The Institution of Electrical Engineers), 1987. 

Solar-based strategies for the conversion of the sun s light to electrical and chemical energy required the discovery of a new generation of specifically designed and engineered photonic materials. Examples of these inorganic semiconductors include those based on amorphous silicon, cadmium telluride, and more complex ternary or quaternary combinations such as copper iridium diselenide or dye-sensitized semiconductors. 

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. 

Semiconductor - Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoitaic conversion process. 

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. 

Phases formed on semiconductor surfaces can change the electrical properties in an uncontrolled, deleterious fashion. Oxide passivation layers on compound semiconductors (e.g., mercury cadmium telluride IR detectors or gallium arsenide solar cells) can be grown to impart protection to the surfaces and to stabilize electrical properties by preventing uncontrolled reactions. 

---