Showing papers on "Energy conversion efficiency published in 1982"

Efficiency of hot-carrier solar energy converters

Abstract: A single‐threshold quantum‐utilizing device in which the excited carriers thermally equilibrate among themselves, but not with the environment, can convert solar energy with an efficiency approaching that of an infinite‐threshold device. Such a hot‐carrier flat‐plate device operated under typical terrestrial conditions (AM 1.5 illumination, 300 K) can convert solar energy with an efficiency of 66%, substantially exceeding the 33% maximum efficiency of a quantum device operating at thermal equilibrium, and the 52% maximum efficiency of an ideal thermal conversion device. This high efficiency is achieved in part through an unusual inversion, in which the chemical potential of the excited electronic band is below that of the ground band. This negative potential difference reduces radiation losses, permitting a low threshold energy, and a high Carnot efficiency resulting from a high carrier temperature.

Observation of stimulated Brillouin scattering in low-loss silica fibre at 1.3 μm

Abstract: Stimulated Brillouin scattering (SBS) in low-loss single-mode silica fibre is observed at 1.32 μm using a continuous-wave single-frequency Nd:YAG laser. The threshold for SBS is 5 mW and the transmitted power reaches a saturated maximum for launch powers exceeding about 10 mW. A conversion efficiency of 65% is observed. The Stokes frequency shift is 12.7±0.2 GHz.

Tunable infrared solid-state laser materials based on Cr 3+ in low ligand fields

Abstract: A new class of solid-state tunable lasers based on Cr3+in low ligand field materials is described. Spectroscopic and calculated laser properties have been obtained for the4T 2 emission in two low field crystals: K 2 NaSc 1-x Cr x F 6 and Al 1-x Cr x (PO 3 )3. A comparison is made with two d3laser materials (Cr3+: alexandrite and V2+:MgF 2 . The prospect of expanding this class of materials is assessed.

High efficieincy direct conversion of heat to electrical energy-related pyroelectric measurements

Abstract: An estimate of the intrinsic thermodynamic efficiency of heat to electrical energy conversion of a specific ferroelectric material, Pb0.99Nb0.02(Zr0.68,Sn0.25Ti0.07)0.98O3, is made. Measurements of pyroelectric effect, electrocaloric effect and polarization versus electric field are combined to yield an efficiency estimate which is greater than 80% of the Carnot value for a cycle which employes heat regeneration. For an ideal multiple-stage heat engine a system efficiency of 30% would result. Practical limitations are also discussed.

Improved efficiency of n‐CdSe thin‐film photoelectrodes by zinc surface treatment

Abstract: The open circuit voltage, fill factor, and power conversion efficiency of n‐CdSe thin‐film electrodes for photoelectrochemical solar cells have been improved by treating the surface with Zn++ ions. The overall efficiency of these electrodes was increased from ∼5% to as high as 6.5% with a soaking treatment in 1 M ZnC12. Photoelectrochemical measurement and Auger spectroscopy indicated the observed improvements were the result of a shift in the flat‐band potential to more negative values due to the incorporation of zinc into the surface region of the CdSe thin film.

Semiconductor based photoelectrochemical cells for solar energy conversion—An overview

Abstract: An overview of the semiconductor based photoelectrochemical (pec) cells for solar energy conversion is presented.pec cells are of two types: photoelectrolysis cells and photovoltaic cells. The principles involved, electrode and electrode/electrolyte interface characteristics, experimental methods of investigation and energy conversion efficiency are discussed in detail. Up-to-date data on variouspec cells are also presented and discussed.

Optical frequency conversion in quasi-phase-matched stacks of nonlinear crystals

Abstract: We present a quantitative theory of nonlinear frequency conversion in stacks of crystals where the phase mismatch due to dispersion is compensated by changing the sign of the nonlinear coupling coefficient in successive crystals-a method first proposed by Armstrong et al. We include pump depletion in our calculations of the second harmonic generation and sum and difference frequency generation. We start with ideal stacks in which the crystal lengths are tailored to achieve perfect phase compensation. When the conversion in each coherence length is small, all crystal lengths tend to equal the coherence length \pi/\Deltak . Frequency conversion in such stacks is well approximated by that in an equivalent phase-matched crystal with the nonlinear coupling coefficient reduced by a factor of 2/\pi . The effect of systematic as well as random departures in crystal lengths are studied with special attention to the evolution of the relative phase. We show that with appropriate choice of the signs of the nonlinear coupling coefficient in various crystals, high efficiency frequency conversion should be possible using practically any sufficiently large set of nonlinear crystals. The theory of second harmonic generation in periodic stacks and in rotationally twinned crystals of zinc-blend structure is described in detail.

Mode converters used in the Doublet III ECH microwave system

Abstract: Woveguide mode converters aro used in the 60 GHz, 200 KW plasma heating system for Doublet III both to convert from the TE02 to the more convenient. TE01 mode for transmission and to convert from the TE01 to the TE11mode to produce a linear polarization at the antenna. Both converters line periodic wall porturbations, the former having circularly symmetric perturbations and the latter periodic curvature (m = 1) perturbations. The TE02 to TE01 converter shows a conversion efficiency of at least 95% (99% predicted) while the TE01 to TE11 convertor has a 90% conversion efficiency (92% predicted). The frequency sensitivity of these devices will be discussed.

A high efficiency single‐crystal CdSe photoelectrochemical solar cell and an associated loss mechanism

Abstract: The conversion efficiency of a n‐CdSe (1120) photoelectrochemical solar cell was found to be 12.4% in alkaline K3Fe(CN)6/K4Fe(CN)6 electrolyte. The pH of the electrolyte is critical for observing high efficiency and stable photocurrent. A selenium corrosion layer acts as a light filter to block the photocurrent.

Photoelectrochemical Behavior of n‐Si Electrodes Protected with Pt‐Polypyrrole

Abstract: Highly stable photoanodes based on single crystal n-Si protected with a thin coating of Pt and electrochemically grown polypyrrole films have been studied. A power conversion efficiency of 5.5% under illumination of 55 mW/cm/sup 2/ tungsten-halogen light is reported with an iodide/triiodide electrolyte. The cells exhibit long-term stability over a time period of weeks. The operating characteristics of the junctions yield high fill factors and rapid electron transfer kinetics at the interface. Values of the junction quality factor as low as 1.1 have been achieved showing almost ideal Schottky junction behavior. The open-circuit voltage as a function of the redox potential of the electrolyte shows substantial Fermi level pinning at the interface. The physical structure of the junctions has been studied with AES sputter profiling techniques. The main factor limiting the power conversion efficiency of the present devices is low short-circuit photocurrent due to light absorption in the concentrated iodide/triiodide electrolyte. 11 refs.

Design of a 13% efficient n-GaAs 1−x P x semiconductor–liquid junction solar cell

Abstract: We report here the design of the most efficient non-aqueous semiconductor–liquid junction solar cell studied to date. Our approach involves the use of ternary semiconductor electrodes made from solid solutions of a large hand gap material, GaP, and a small band gap material, GaAs. We demonstrate here that photoanodes consisting of such materials are capable of simultaneously yielding high open circuit voltages and favourable wavelength response to the solar spectrum. A few n-type semiconductor–liquid junction solar cells in aqueous solutions have been reported to yield high (>10%) solar-to-electrical conversion efficiencies1–3. However, for most materials, rapid photoanodic corrosion dominates the interfacial photochemistry4–8. Non-aqueous solvent systems can suppress electrode decay due to corrosion4,7,8; but modest (<6%) conversion efficiencies have been observed for all photoanodes studied in solar irradiation conditions9–13. The photoanodes used here yield over 13% solar-to-electrical conversion efficiencies, or more than double the efficiency of any other non-aqueous semiconductor–liquid junction solar cell previously reported.

Valency Control of Glow Discharge Produced a-SiC:H and its Application to Heterojunction Solar Cells

Abstract: A new type of amorphous silicon solar cell having a conversion efficiency of 8% level is introduced. The cell has a wide band gap window layer made of hydrogenated amorphous silicon carbide, (a-SiC:H), with a good valency control. Electrical, optical and optoelectronic properties of a-SiC:H have been investigated, together with their valency controllability. A design concept and some key technologies to improve solar cell performance with this new material are demonstrated. A series of technical data on material preparation and cell performance are presented. Clear improvements in cell performance, not only IDC but also VDC, have been obtained. The realistic limit of the conversion efficiency in a-Si solar cells is estimated and discussed.

An efficient, small scale chemical oxygen‐iodine laser

Abstract: More than 40% extractable power efficiency has been achieved in a transverse flow, small scale, chemically pumped iodine‐atom laser. 5 W of cw laser emission at 1315 nm has been obtained via energy transfer from chemically generated O2(1Δ) to I atoms in a 10×1 cm2 rectangular flow duct. Simple construction materials, safely handled chemicals, and a medium size vacuum pump were used for fabricating and operating the laser. The importance of minimizing quenching of excited species by collision with water molecules or with the wall is demonstrated.

Preparation and Properties of Amorphous Silicon Produced by a Consecutive, Separated Reaction Chamber Method

Abstract: A new method of preparing a-Si film, in which each of the p, i, and n layers are deposited in consecutive, separated reaction chambers, is presented. It was confirmed experimentally that, in the conventional single reaction chamber method for a-Si film, the residual dopant gases which remain in the reaction chamber cause undesirable doping of the film, resulting in deterioration of the film quality. This undesirable doping can be avoided in the separated reaction chamber method. The photoconductivity of the i-layer prepared by this method was about 1×10-3 (Ω-1cm-1) in sunlight of AM–1 100 mW/cm-2. The best conversion efficiency of p-i-n a-Si solar cells prepared by this method was 6.91%.

High‐efficiency organometallic vapor phase epitaxy AlGaAs/GaAs monolithic cascade solar cell using metal interconnects

Abstract: A two‐junction solar cell has been fabricated using an Al0.30Ga0.70As (1.82 eV) tap cell and a GaAs (1.43 eV) bottom cell. A processed metal interconnect is used to connect the two cells together in series. An efficiency of 21.5% at 980 mW/cm2 has been measured in a solar simulator with an open circuit voltage of 2.35 V, a short circuit current of 118.6 mA/cm2, and a fill factor of 0.76. An efficiency of 22% has been measured under 130 AM3 sun in a solar tracking concentrator. Organometallic vapor phase epitaxy is used to grow the entire nine‐layer device.

Effect of thickness on silicon solar cell efficiency

Abstract: Semiconductor material cost is one of the factors which determines the performance-cost ratio and economical feasibility of silicon solar cells for terrestrial power generation. Decreasing the cell thickness would lower the silicon material cost. The energy conversion efficiency of a back-surface field solar cell will have a peak as the silicon film thickness is reduced due to two opposing factors: 1) the open-circuit voltage increases and 2) the short-circuit current decreases with decreasing cell thickness. A computer-aided-design study on the dependence of this efficiency peak on the concentrations of the recombination and dopant impurities is presented in this paper. The illuminated current-voltage characteristics of over 100 cell designs were obtained using the transmission line circuit model to numerically solve the Shockley equations. Using an AM1 efficiency of 17 percent as a target value, which is the highest encapsulated silicon cell efficiency used in the Block IV modules of the Low-Cost Solar Array Project, it is shown that the efficiency versus thickness dependence has a broad maximum which varies less than 1 percent over more than a three-to-one range of cell thickness from 30 to 100 µm. Optical reflecting back surface will give only a slight improvement of AM1 efficiency, about 0.7 percent, in this thickness range. The sensitive dependence of efficiency on patchiness across the back-surface field low-high junction in thin cells is noted.

Spray‐Pyrolyzed Thin Film CdSe Photoelectrochemical Cells

Abstract: Spray-pyrolyzed CdSe thin films have been prepared and used as anodes in photoelectrochemical cells. The efficiency of these cells can be enhanced by annealing of the thin film electrodes in air and subsequently photoactivating in slightly acidic salt solutions. The overall efficiency for optical to electrochemical energy conversion is 17.5% at 640 nm and 6.4% under simulated sunlight. 12 refs.

Photoelectric conversion semiconductor device

Abstract: PURPOSE:To prevent the reliability of a semiconductor device from decreasing due to the reaction of metal with semiconductor device by forming a back surface electrode in a 2-layer structure of a light transmittance conductive film and a reflecting metal layer, thereby improving the conversion efficiency. CONSTITUTION:The first light transmittance conductive film CTF2 is formed on a glass substrate 1. Then, a photovoltaic power generating non-single crystal semiconductor 3 which has a PIN or P-N junction is formed on the CTF2. Then, the second light transmittance conductive film 5 having a thickness of 700- 2,000Angstrom and the second electrode formed of a reflecting metal layer 6 on the film 5 are formed on an N type semiconductor of the semiconductor 3. When thus constructed, short wavelength of 500nm or shorter is sufficiently absorbed by the light passing in forth, and long wavelength of 600nm or longer can generate photocarrier at the active semiconductor layer by the light of return after reflecting. The film 5 operates to prevent the reaction of aluminum forming the layer 6 with Si, thereby preventing the lowering in its reliability.

Amorphous silicon p‐i‐n solar cells fabricated by reactive sputtering

Abstract: We report, for the first time, the fabrication of indium‐tin‐oxide p‐i‐n amorphous silicon solar cells by the method of reactive sputtering. These solar cells exhibit power conversion efficiency of 4.0% under AM1 illumination. The junction characteristics of these solar cells are discussed.

Monolithic Integration of a Dielectric Millimeter-Wave Antenna and Mixer Diode: An Embryonic Millimeter-Wave IC

Abstract: A monolithic silicon integrated circuit consisting of a mixer diode and an all-dielectric receiving antenna has been built and tested at 85 GHz. Radiation is coupled into the device optically with a coupling loss of 2.7 dB. No external metal structure is required for coupling. The design can be used efficiently at considerably higher frequencies, and can be elaborated into more complex integrated circuits. From measurements of video responsivity the losses of various parts of the device are estimated. A simple theory of conversion efficiency is found to agree well with experiment this theory is then used to predict the performance of improved versions of the device. The conversion efficiency obtained with this demonstration device is low; it is shown, however, that acceptable conversion efficiencies can be obtained with a more advanced diode fabrication technology using epitaxial Si or GaAs. Integrated millimeter-wave receivers of this kind should be suitable for short-path terrestrial communications, in applications where compactness and low cost are required.

Efficient Raman frequency conversion in liquid nitrogen

Abstract: The single-pass efficiency of stimulated Raman scattering in liquid N 2 has been investigated under tight-focusing and collimated-beam conditions keeping the gain-length products approximately constant. In collimated-beam geometry, the gain-length is much greater than important four-wave mixing phasematching coherence lengths, and a 92 percent quantum (80 percent energy) efficiency for generation of the first Stokes Raman output is reported. In the much shorter confocal parameter tight-focusing geometry, parametric processes couple the scattered energy into a number of higher order Stokes components and limit the conversion efficiency into any single component.

Experimental results from a beam direct converter at 100 kV

Abstract: A direct-energy converter was developed for use on neutral-beam injectors. The purpose of the converter is to raise the efficiency of the injector by recovering the portion of the ion beam not converted to neutrals. In addition to increasing the power efficiency, direct conversion reduces the requirements on power supplies and eases the beam dump problem. The converter was tested at Lawrence Berkeley Laboratory on a reduced-area version of a neutral-beam injector developed for use on the Tokamak Fusion Test Reactor at Princeton. The conversion efficiency of the total ion power was 65 ±7% at the beginning of the pulse, decaying to just over 50% by the end of the 0.6-s pulse. Once the electrode surfaces were conditioned, the decay was due to the rise in pressure of only the beam gas and not to outgassing. The direct converter was tested with 1.7 A of hydrogen ions and with 1.5 A of helium ions through the aperture with similar efficiencies. At the midplane through the beam, the line power density was 0.7 MW/m, for comparison with our calculations of slab beams and the prediction of 2–4 MW/m in some reactor studies. Over 98 kV was developed at the ion collector when the beam energy was 100 keV. When electrons were suppressed magnetically, rather than electrostatically, the efficiency dropped to 40%. However, a better designed electron catcher could improve this efficiency. New electrode material released gas (mostly H2 and CO) in amounts that exceeded the input of primary gas from the beam. The electrodes were all made of 0.51-mm-thick molybdenum cooled only by radiation. This allowed the heating by the beam to outgas the electrodes and for them to stay hot enough to avoid the reabsorption of gas between shots. By minor redesign of the electrodes, adding cryopanels near the electrodes, and grounding the ion source, these results extrapolate with high confidence to an efficiency of 70–80% at a power density of 2–4 MW/m. Higher power may be possible with magnetic electron suppression.

Second harmonic light generation in the rabbit cornea.

Abstract: The conversion efficiency for second harmonic generation of light in a rabbit cornea from a pulsed YAG laser has been measured to be 6 x 10(-9) for an input power density of 1 MW/cm(2). Because of this low efficiency it does not seem likely that second harmonic energy generated in the corena could cause retinal damage. These results do not rule out the possibility that there is a similar effect occurring in the retina.

Amorphous semiconductor and amorphous silicon photovoltaic device

Abstract: An amorphous silicon semiconductor of the general formula: a-Sisub(1-x-y) C x N y containing hydrogen and/or fluorine, which provides an amorphous silicon PIN junction photovoltaic device having an improved conversion efficiency when it is used as a P-type or N-type layer on the light impinging side of the PIN junction photovoltaic device Also, the conversion efficiency of an amorphous silicon PIN junction photovoltaic device is improved by using a two-layer film structure of ITO and SnO 2 as a transparent electrode for the photovoltaic device, with the SnO 2 layer contacting the P or N layer The improvement is particularly marked in the case of heterojunction photovoltaic devices