3,383 research outputs found
Expression of the angular dependence of the quantum efficiency for a thin multi-alkali photocathode and its optical properties
The dependence of the quantum efficiency on the angle and polarization of the
incident photon needs to be formulated for a precise description of the
response of photomultiplier tubes. A simplified one-step model of photoelectron
emission was derived from Spicer's three-step model, and it enabled the
formulation of the dependence of the quantum efficiency in the visible range
for thin multi-alkali (NaKSbCs) photocathodes. The expression of the quantum
efficiency was proved by a measurement of the photocurrent for linearly
polarized light at various incident angles. Meanwhile, the measurement revealed
the complex refractive indices and thicknesses both of the stratified
photocathode and antireflection coating. It is indicated that the angular
dependence of the quantum efficiency is dictated by the optical properties of
the photocathode, which are discussed in detail on the basis of the obtained
parameters
Optimization of contaminated oxide inversion layer solar cell
Contaminated oxide cells have been fabricated with efficiencies of 8.6% with values of I sub sc = 120 ma, V sub oc = .54 volts, and curve factor of .73. Attempts to optimize the fabrication step to yield a higher output have not been successful. The fundamental limitation is the inadequate antireflection coating afforded by the silicon dioxide coating used to hold the contaminating ions. Coatings of SiO, therefore, were used to obtain a good antireflection coating, but the thinness of the coatings prevented a large concentration of the contaminating ions, and the cells was weak. Data of the best cell were .52 volts V sub oc, 110 ma I sub sc, .66 CFF and 6.7% efficiency
Method For Low Temperature Plasma Enhanced Chemical Vapor Deposition (pecvd) Of An Oxide And Nitride Antireflection Coating On Silicon
A sequential plasma-enhanced chemical vapor deposition (PECVD) of SiN and SiOx produces a very effective double-layer antireflection coating. This antireflection coating is compared with the frequently used and highly efficient double-layer MgFâ‚‚ /ZnS coating. It is shown that the double-layer SiOx /SiN coating improves the short-circuited current (Jsc) by 47%, open-circuit voltage (Voc) by 3.7%, and efficiency (Eff) by 55% for silicon cells with oxide surface passivation. The counterpart MgFâ‚‚ /ZnS coating gives smaller improvement in Voc and Eff. However, if silicon cells do not have the oxide passivation, the PECVD SiOx /SiN gives much greater improvement in the cell parameters, 57% in Jsc, 8% in Voc, and 66% in efficiency, compared to the MgFâ‚‚ /ZnS coating which improves Jsc by 50%, Voc by 2%, and cell efficiency by 54%. This significant additional improvement results from the PECVD deposition-induced surface/defect passivation. The internal quantum efficiency (IQE) measurements showed that the PECVD SiOx /SiN coating absorbs fair amount of photons in the short-wavelength range ( <500 nm), however, the improved surface/defect passivation more than compensates for the loss in Jsc and gives higher improvement in the cell efficiency compared to the MgF i/ZnS coating.Georgia Tech Research Corporatio
Processes For Producing Low Cost, High Efficiency Silicon Solar Cells
Processes which utilize rapid thermal processing (RTP) are provided for inexpensively producing high efficiency silicon solar cells. The RTP processes preserve minority carrier bulk lifetime Ï„ and permit selective adjustment of the depth of the diffused regions, including emitter and back surface field (bsf), within the silicon substrate. In a first RTP process, an RTP step is utilized to simultaneously diffuse phosphorus and aluminum into the front and back surfaces, respectively, of a silicon substrate. Moreover, an in situ controlled cooling procedure preserves the carrier bulk lifetime Ï„ and permits selective adjustment of the depth of the diffused regions. In a second RTP process, both simultaneous diffusion of the phosphorus and aluminum as well as annealing of the front and back contacts are accomplished during the RTP step. In a third RTP process, the RTP step accomplishes simultaneous diffusion of the phosphorus and aluminum, annealing of the contacts, and annealing of a double-layer antireflection/passivation coating SiN/SiOx. In a fourth RTP process, the process of applying front and back contacts is broken up into two separate respective steps, which enhances the efficiency of the cells, at a slight time expense. In a fifth RTP process, a second RTP step is utilized to fire and adhere the screen printed or evaporated contacts to the structure.Georgia Tech Research Corporatio
A millimeter-wave antireflection coating for cryogenic silicon lenses
We have developed and tested an antireflection (AR) coating method for
silicon lenses at cryogenic temperatures and millimeter wavelengths. Our
particular application is a measurement of the cosmic microwave background. The
coating consists of machined pieces of Cirlex glued to the silicon. The
measured reflection from an AR coated flat piece is less than 1.5% at the
design wavelength. The coating has been applied to flats and lenses and has
survived multiple thermal cycles from 300 to 4 K. We present the manufacturing
method, the material properties, the tests performed, and estimates of the loss
that can be achieved in practical lenses
A reliable all-silver front contact for silicon solar cells
The feasibility of making an adherent and moisture degradation resistant silver-only front contact to silicon solar cells was demonstrated. Optimum fabrication processes and process sequences were determined for making such contacts. These contacts were found to also have good electrical characteristics. A back contact of aluminum-silver was also developed. This proved very satisfactory for low-temperature applications
Simulation comparisons of monitoring strategies in narrow bandpass filters and
antireflection coating
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