Showing papers on "Energy conversion efficiency published in 1994"

Efficiency improvements of silicon solar cells by the impurity photovoltaic effect

Abstract: A theoretical investigation of the impurity photovoltaic (IPV) effect for improving silicon solar‐cell efficiency is presented. The approach is better than previous analyses because of the improved treatment of generation and recombination via impurities, and because it includes the effects of optical competition and light trapping. The approach is applied to the nonmidgap, deep‐level impurity indium as the IPV effect impurity incorporated into an idealized silicon solar cell. The analysis is based on experimentally determined parameters for indium. Improvements of cell current, subgap spectral response, and energy conversion efficiency are quantified. The analysis reveals the importance of light trapping and proper selection of indium and dopant concentrations. The impurity photovoltaic effect is predicted to improve solar‐cell efficiency.

Efficiency of broadband four-wave mixing wavelength conversion using semiconductor traveling-wave amplifiers

Abstract: We present a theoretical analysis and experimental measurements of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers. In the theoretical analysis, we obtain an analytical expression for the conversion efficiency. In the experiments, both up and down-conversion efficiencies are measured as a function of wavelength shift for shifts up to 27 nm. The experimental data are well explained by the theoretical calculation. The observed higher conversion efficiency for wavelength down-conversion is believed to be caused by phase interferences that exist between various mechanisms contributing to the four-wave mixing process. >

High-efficiency a-Si/c-Si heterojunction solar cell

Abstract: An aperture-area conversion efficiency of 20.0% (intrinsic efficiency: 21.0%) has been achieved for a 1.0 cm/sup 2/ CZ n-type single crystalline silicon (c-Si) solar cell, by using the "HIT (heterojunction with intrinsic thin-layer)" structure on both sides of the cell. This is the world's highest value for a c-Si solar cell in which the junction is fabricated at a low temperature of below 200/spl deg/C. In this paper, the junction fabrication technologies and features of the HIT structure are reviewed. The stability under light and thermal exposure, and the temperature dependence on performance of a high-efficiency HIT solar cell are also reported.

Four-wave mixing wavelength conversion efficiency in semiconductor traveling-wave amplifiers measured to 65 nm of wavelength shift

Abstract: The efficiency of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers is measured for wavelength shifts up to 65 nm using a tandem amplifier geometry. A quantity we call the relative conversion efficiency function, which determines the strength of the four-wave mixing nonlinearity, was extracted from the data. Using this quantity, gain requirements for lossless four-wave mixing wavelength conversion are calculated and discussed. Signal to background noise ratio is also measured and discussed in this study. >

Numerical modeling of the optical properties of hydrogenated amorphous‐silicon‐based p‐i‐n solar cells deposited on rough transparent conducting oxide substrates

Abstract: Hydrogenated amorphous‐silicon (a‐Si:H) ‐based solar cells consist of two electrodes and a p‐i‐n structure, deposited on glass substrates. Depositing the p‐i‐n layers and the back metallic electrode on an optically rough transparent conducting oxide (TCO) electrode enhances the absorption of the incident light in the active i layer: Light is scattered at the rough front interface and is partially trapped in the high refraction index layer, as in a waveguide. In addition TCO roughness increases the front transmission coefficient, increasing the amount of light in the active layer. TCO texture yields a relative increase of the conversion efficiency up to 30%. A semiempirical model of thin‐film solar‐cell optics is presented, taking into account the interface roughness by introducing experimentally derived scattering coefficients and treating the propagation of specular light in a rigorous way. Numerically simulated spectral response and total reflectance of standard solar cells deposited on different TCO textures are compared to experimental data. The results show a better fit to measured characteristics than simulations obtained by previous semiempirical modeling. Improvements mainly come from the light propagation calculation. According to the model, the number of passes incident light may make through the active i layer reaches six for the most efficient cell. As an example of the model’s main application, the enhancement of the conversion efficiency that would be expected from an optimized TCO layer is calculated for each texture studied and for different back metallizations.

Solid-state multiple-prism grating dye-laser oscillators.

Abstract: Compact solid-state multiple-prism grating dye-laser oscillators are shown to yield in excess of 9% conversion efficiency at Δν ≈ 1.12 GHz and a tuning range of 47 nm.

Noncritical quasi-phase-matched second harmonic generation in an annealed proton-exchanged LiNbO/sub 3/ waveguide

Abstract: We report the demonstration of dimensional noncritical phase matching, a phase-matched interaction length exceeding 10 mm, and an internal conversion efficiency of 204%/W for second harmonic generation of 976 nm radiation in a periodically poled, annealed proton-exchanged LiNbO/sub 3/ waveguide. Using models for the linear and nonlinear optical properties of annealed proton-exchanged LiNbO/sub 3/ waveguides and the observed ferroelectric domain grating, the phase-matching wavelength was predicted to within several nm and the conversion efficiency to within /spl ap/20% of the measured values. Optimization of waveguide second harmonic generation devices is discussed. >

Milliwatt output levels and superquadratic bias dependence in a low‐temperature‐grown GaAs photomixer

Abstract: A cw output power up to 08 mW is obtained from a low‐temperature‐grown (LTG) GaAs, 03 μm gap, interdigitated‐electrode photomixer operating at room temperature and pumped by two modes of a Ti:Al2O3 laser separated in frequency by 02 GHz The output power and associated optical‐to‐electrical conversion efficiency of 1% represent more than a sixfold increase over previous LTG‐GaAs photomixer results obtained at room temperature A separate LTG‐GaAs photomixer having 06 μm gaps generated up to 01 mW at room temperature and up to 4 mW at 77 K Low‐temperature operation is beneficial because it reduces the possibility of thermal burnout and it accentuates a nearly quartic dependence of output power on bias voltage at high bias The quartic dependence is explained by space‐charge effects which result from the application of a very high electric field in the presence of recombination‐limited transport These conditions yield a photocurrent‐voltage characteristic that is very similar in form to the well‐known Mott–Gurney square‐law current in trap‐free solids

Vertical cavity surface emitting lasers with 21% efficiency by metalorganic vapor phase epitaxy

Abstract: Proton implanted, vertical cavity top-surface emitting lasers exhibit the highest single-mode and multi-mode output powers, highest power conversion efficiency, and lowest threshold voltage for such devices reported to date. These lasers use new mirror grading designs that are enabled by metalorganic vapor phase epitaxy's capabilities of alloy grading and carbon doping. The results validate this growth technology by exceeding the previous best results which were based on molecular beam epitaxy. >

Accelerated publication 16.4% total‐area conversion efficiency thin‐film polycrystalline MgF2/ZnO/CdS/Cu(In,Ga)Se2/Mo solar cell

Abstract: This communication reports an MgF2/ZnO/CdS/Cu(In,Ga)Se2/Mo/glass polycrystalline solar cell with a confirmed total-area conversion efficiency of 16.4%. the thin-film Cu(In,Ga)Se2 absorber was fabricated by computer-controlled physical vapor deposition (PVD) from the elemental sources. the resulting absorber has a Gal/In compositional grading that we refer to as a notch. Capacitance-voltage (C-V) measurements also reveal a graded doping profile in the region near the electronic p-n junction. the enhanced device performance is characterized by an open-circuit voltage (Voc) of 660 mV and a particularly high fill factor (FF) of 78.7%.

Analytical theory of four-wave mixing in semiconductor amplifiers.

Abstract: The analytical theory of four-wave mixing in semiconductor amplifiers is developed. The theory applies to arbitrary saturation conditions. If carrier depletion and spectral hole burning are considered, the conversion efficiency is the maximum at a total input power that produces a gain compression of e−2 (approximately −9 dB), independently of the physical parameters of the amplifier.

Optical parametric frequency conversion properties of KTiOAsO4

Abstract: The new nonlinear optical crystal KTiOAsO4 (KTA) is characterized and evaluated for use in optical parametric oscillator devices (OPOs) capable of generating tunable radiation in the 3–5 μm region. Parametric tuning curves at the pump wavelength of 1.064 μm are measured and compared to predictions based on published Sellmeier equations. Oscillation thresholds and damage thresholds of KTA are measured relative to its well‐known isomorph KTiOPO4 (KTP). A KTA OPO was constructed which obtained a maximum conversion efficiency of 20% when pumped 2.6 times above threshold. Our results demonstrate that KTA is a promising material for use in optical parametric devices.

In2O3/CdS/CuInS2 thin-film solar cell with 9.7% efficiency

Abstract: An efficient thin-film photovoltaic cell has been fabricated using the heterostructure consisting of a CuInS2 film obtained by sulfurization of a metallic precursor, a chemical-bath-deposited CdS layer, and an atom-beam-sputtered In2O3 film. A preceding KCN treatment of the Cu-rich CuInS2 film lowered the Cu/In ratio and raised the resistivity. A cell conversion efficiency of 9.7% (active area efficiency>10%) at air mass 1.5 has been achieved without antireflection coatings.

Highly efficient 1.064 µm upconversion pumped 1.47 µm thulium doped fluoride fibre amplifier

Abstract: A highly efficient amplifier has been demonstrated using the 1470 nm transition in a thulium doped fluoride fibre by upconversion pumping at 1064 nm A small signal gain bandwidth of 35 nm was shown with a gain peak of around 19 dB occurring at 1462 nm A maximum gain efficiency of 024 dB/mW, and output power of l7 dBm have been achieved, the latter for a launched pump power of 155 mW, indicating a power conversion efficiency of 34%< >

A dual polarized circular patch rectifying antenna at 2.45 GHz for microwave power conversion and detection

Abstract: A novel circular patch rectifying antenna (rectenna) has been developed which converts microwave energy into DC power at 2.45 GHz. Dual polarization is achieved by two orthogonal microstrip feed lines. Rectification is achieved by GaAs Schottky-barrier diodes located on each feed line. A 48% conversion efficiency from microwave power to DC power was achieved. The design was based on a nonlinear circuit analysis. >

24% efficient silicon solar cells

Abstract: This paper reports significant progress in silicon solar cell performance, taking confirmed efficiency beyond 24% for the first time. This progress has been achieved by a combination of several mechanisms. One is the reduction of recombination at the cell front surface by improved passivation of the silicon/silicon dioxide interface. Resistive losses in the cell have been reduced by a double-plating process which increases the thickness for the coarse cell metallization features. Finally, reflective losses have been reduced by the application of a double layer anti-reflection (DLAR) coating. Another advantage of DLAR coating is that it will give further 3% higher current density than the SiO/sub 2/ single layer antireflection (SLAR) coated cells when encapsulated into modules. The cells display a monochromatic light energy conversion efficiency of 46.3% for 1.04 /spl mu/m wavelength light, also the highest ever for a silicon device.

82% Efficient continuous-wave frequency doubling of 1.06 microm with a monolithic MgO:LiNbO(3) resonator.

Abstract: We describe a frequency-doubling monolithic standing-wave resonator made of MgO:LiNbO(3) with dielectric mirror coatings for impedance matching near 100 mW input power and near-optimum nonlinear coupling. An external conversion efficiency of 82% has been achieved.

Design of highly efficient four-wave mixing devices using optical fibers

Abstract: A design theory of the four-wave mixing (FWM) devices using optical fibers is presented. We find that the signal-to-idler conversion process in the zero-dispersion wavelength region yields the widest conversion bandwidth, and the conversion efficiency can be maximized by choosing the optimum fiber length. The maximum conversion efficiency thus obtained is proportional to the square of the input pump power, but is limited by the stimulated Brillouin scattering (SBS) process in the fiber. We show experimentally the improvement of the conversion efficiency by the SBS suppression and the validation of the proposed theory. >

Intracavity frequency doubling of a continuous-wave, diode-laser-pumped neodymium lanthanum scandium borate laser.

Abstract: Neodymium-doped lanthanum scandium borate [Nd:LaSc3(BO3)4] is a new material for efficient and compact diode-pumped solid-state lasers. A simple plane–plane 3-mm-long resonator is formed by a coated Nd(10%):LaSc3(BO3)4 crystal and a coated potassium titanyl phosphate (KTP) crystal. The second-harmonic output power at 531 nm is 522 mW at 2.05-W incident pump power of the diode laser. The corresponding optical efficiency is 25%, and the conversion efficiency from the fundamental to the second harmonic is 55%. The well-known chaotic power fluctuations of intracavity frequency-doubled lasers (green problem) are avoided by use of a short KTP crystal, between 0.5 and 2 mm in length.

Method for producing textured substrates for thin-film photovoltaic cells

Abstract: The invention pertains to the production of ceramic substrates used in the manufacture of thin-film photovoltaic cells used for directly converting solar energy to electrical energy. Elongated ribbon-like sheets of substrate precursor containing a mixture of ceramic particulates, a binder, and a plasticizer are formed and then while green provided with a mechanically textured surface region used for supporting the thin film semiconductor of the photovoltaic cell when the sheets of the substrate precursor are subsequently cut into substrate-sized shapes and then sintered. The textured surface pattern on the substrate provides enhanced light trapping and collection for substantially increasing the, solar energy conversion efficiency of thin-film photovoltaic cells.

Highly efficient conversion and parametric gain of nondegenerate forward four-wave mixing in a singlemode fibre

Abstract: Highly efficient nondegenerate forward four-wave mixing in a singlemode fibre was achieved by suppressing the stimulated Brillouin scattering of pump light. A conversion efficiency of -4.6 dB, including a fibre loss of 5.3 dB, was obtained at a pump power of +17 dBm with an associated internal parametric gain of 3.3 dB.

Er/sup 3+/:YAlO/sub 3/ upconversion laser

Abstract: Upconversion lasing in Er:YAlO/sub 3/ is reported. Laser emission was produced using both sequential two-step pumping and cross-relaxation energy transfer. In addition, photon avalanche upconversion pumping was demonstrated. Selection among these pumping mechanisms is determined by the pump wavelength, and laser operation was obtained with excitation between 785 nm and 840 nm. The highest laser output power was achieved at 34/spl deg/K, where 918 mW of pump power at 807 nm produced 121 mW of TEM/sub 00/ emission. The optical conversion efficiency was 13%. Repetitively Q-switched operation is reported, and the temporal- and temperature-dependence of the laser output is discussed. >

Switching type DC-DC converter having increasing conversion efficiency at light load

Abstract: In a switching type DC-DC converter, switching frequency f, gate to source voltage of a switching FET, and the stray capacity of the FET are decreased at light load period to increase conversion efficiency at light load. In another embodiment, no-load current is decreased by increasing self inductance of a smoothing choke at light load.

Frequency doubling of 100-fs pulses with 50% efficiency by use of a resonant enhancement cavity.

Abstract: The use of a resonant cavity for efficient second-harmonic generation with 100-fs pulses is demonstrated. With 2-nJ pulses from a mode-locked Cr:forsterite laser, 53% conversion efficiency to the second harmonic at 625 nm is achieved while ~100-fs duration is maintained. This is an order-of-magnitude improvement over the conversion efficiency obtained directly with the laser output.

MOCVD growth of GaAsP on Si for tandem solar cell application

Abstract: In this paper, the crystal growth of GaAsP on Si substrate for solar cell application and the characteristics of GaAsP/Si monolithic tandem solar cells are described. The conversion efficiency is improved by using thermal cycle annealing (TCA) and a graded buffer layer. TEM micrographs show that the dislocation density is drastically decreased with using TCA. The conversion efficiency of GaAsP solar cell on Si with GaAs buffer layer is higher than that with GaP buffer layer. The improvement in the efficiency is obtained by reducing the dislocation density in the GaAsP layer.

Review of solar cell temperature coefficients for space

Abstract: Energy conversion efficiency is an important parameter for solar cells, and well reported in the literature. However, solar cells heat up in sunlight, and the efficiency decreases. The temperature coefficient of the conversion efficiency is thus also extremely important, especially in mission modeling, but is much less well reported. It is of value to have a table which compiles into a single document values of temperature coefficients reported in the literature. In addition to modeling performance of solar cells in Earth orbit, where operating temperatures may range from about 20 C to as high as 85 C, it is of interest to model solar cells for several other recently proposed missions. These include use for the surface of Mars, for solar electric propulsion missions that may range from Venus to the Asteroid belt, and for laser-photovoltaic power that may involve laser intensities equivalent several suns. For all of these applications, variations in operating temperature away from the nominal test conditions result in significant changes in operating performance. In general the efficiency change with temperature is non-linear, however, in the range from negative 100 C through room temperature to a few hundred degrees C, efficiency is usually quite well modeled as a linear function of temperature (except for a few unusual cell types, such as amorphous silicon, and for extremely low bandgap cells, such as InGaAs).