III-V InGaP/InGaAs/Ge triple junction solar cells have been developed which incorporate quantum wells into the InGaAs and InGaP junctions. Characterization of such devices shows an absolute efficiency gain of up to 2% with Voc exceeding that of non-QW devices. Cells grown on 6â² wafers with quantum wells in the InGaAs junction are now commercially available with median efficiencies above 41%
The chemical compounds present on the surface of CdTe have been investigated after different surface preparations and correlated with the properties of junctions formed by Cr on the CdTe. xray photoelectron spectroscopy (XPS) analysis indicates that four different surface compositions result from five different treatments. Cleaving leaves a stoichiometric surface whereas oxidation in air leads to the formation ofTe0 2 . Bromine-in-methanol etch leaves a Te-enriched surface and chromate etch leaves a surface containing both Te0 2 and excess Te. Hydrogen heat treatment of an etched CdTe surface restores a stoichiometric cleavedlike surface from that disrupted by the etching process. Effects on the properties of subsequently formed junctions are evidenced by a decrease in the diode saturation current from 2x lO-s for a bromine-etched surface to 2x 10-8 A/cm 2 for a cleaved surface.
Articles you may be interested inInterfacial deeplevel formation and its effect on band bending at metal/CdTe interfaces J. Vac. Sci. Technol. A 6, 2752 (1988); 10.1116/1.575500Effects of interfacial charge on the electron affinity, work function, and electrical characteristics of thinly oxidized semiconductorinsulatorsemiconductor and metalinsulatorsemiconductor devicesThe effects of surface preparation on the properties of single crystal CdTe junctions have been investigated through characterization of metal/CdTe junctions. Oriented surfaces include aircleaved (110) surfaces, bromine-in-methanol etched (110) and (111) surfaces, and bromine-inmethanol etched surfaces subjected to a hydrogen heat treatment. Surface photovoltage measurements of the surfaces indicate larger band bending on the etched surfaces than on the cleaved and heat treated surfaces. X-ray photoelectron spectroscopy analysis verifies that excess Te remains after bromine-in-methanol etching and that cleaving leaves a stoichiometric surface. Hydrogen heat treatment of an etched CdTe surface restores a stoichiometric cleaved-like surface from that altered by the etching process. The barrier height for metal/CdTe junctions formed on cleaved surfaces depends on metal work function and reaches 0.99 V in an Al/CdTejunction and 0.87 V in a Cr/CdTe junction. Junctions formed with different metals on etched (110) surfaces result in barrier heights of 0.55--0.65 V with no dependence ofthe barrier height on the metal work function being observed, due to the presence of an etch-induced layer that partially governs the properties the surface. Heat treatment of an etched surface results in metal/CdTe junctions with characteristics similar to those of junctions formed on cleaved surfaces, and dependence of barrier height on metal work function is again observed, indicating the removal of an etch-induced layer by the heat treatment and the production of a junction similar to that on the cleaved surface.
Photovoltaic power converters transform optical power into electrical power, which is inherently immune to RF, EMI, high voltage, and lightning effects. Capable of powering electronic circuitry directly over optical fiber in a wide variety of applications, this technology has been validated in industries such as electric power, communications, remote sensing and aerospace. From no more than a laboratory curiosity less than fifteen years ago, power-over-fiber, or photonic power, has established itself in thousands of industrial operations worldwide. Optical energy for pre-amplifiers or lowpower transmitters as well as switches and relays can be efficiently delivered through noise immune and non-conductive optical fiber. These advantages are also readily available for safe and arm applications since optical fiber is immune to electrical noise, magnetic fields and conduction of unexpected electrical currents. Since it is made from glass, a dielectric fiber is impervious to electromagnetic interference. High optical power is readily delivered through fiber, and conversion of optical to electrical energy at the remote site with efficient photovoltaic converters is routine.
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