Showing papers on "Energy conversion efficiency published in 2000"
TL;DR: In this article, an exciton blocking layer (EBL) was inserted between the photoactive organic layers and the metal cathode, achieving an external power conversion efficiency of 2.4%±0.3% in vacuumdeposited ultrathin organic bilayer photovoltaic (PV) cells employed in a simple light trapping geometry.
Abstract: We demonstrate a method for efficient photon harvesting in organic thin films, thereby increasing the efficiency of organic photovoltaic cells. By incorporating an exciton-blocking layer (EBL) inserted between the photoactive organic layers and the metal cathode, we achieved an external power conversion efficiency of 2.4%±0.3% in vacuum-deposited ultrathin organic bilayer photovoltaic (PV) cells employed in a simple light trapping geometry. Ultrathin (∼100 A) cells incorporating the transparent, conductive EBL have an internal quantum efficiency as high as 33%±4% over a spectral region matched to the solar spectrum. The very thin organic layers have a low series resistance, allowing for efficient power conversion in organic PV cells under intense (>15 suns) AM1.5 illumination. This device structure demonstrates that control of exciton diffusion in solid-state organic devices leads to a significant increase in the photon-to-carrier conversion efficiency.
679 citations
01 Oct 2000
TL;DR: In this article, a polycrystalline Nd-doped Y3Al5O12 ceramics was used for the first time to achieve highly efficient laser oscillation at 1064 nm.
Abstract: Optical absorption, emission spectra have been measured for polycrystalline Nd-doped Y3Al5O12 ceramics. Fluorescence lifetimes of 257.6 μs, 237.6 μs, 184.2 μs and 95.6 μs have been obtained for 0.6%, 1%, 2% and 4% neodymium-doped YAG ceramics, respectively. For the first time, highly efficient laser oscillation at 1064 nm has been obtained with this kind of ceramics. Slope efficiency of 53% has been achieved on a uncoated 4.8-mm thick 1% Nd:YAG ceramics sample. Optical to optical conversion efficiency is 47.6%. Laser oscillation has also been obtained with a 2% Nd:YAG ceramics. The optical properties and laser output results have been compared with that of Nd:YAG single crystal grown by the Czochralski method. Almost identical results have been achieved including laser experiments results. But fabrication of Nd:YAG ceramics is much easier compared to the single-crystal growth method. And also large size (now of about 400 mm diameter×5 mm is available) and high-concentration (>1%) Nd:YAG ceramics can be fabricated. The results show that this kind of Nd:YAG ceramics is a very good alternative to Nd:YAG single crystal.
361 citations
TL;DR: In this paper, a cell containing illuminated AlGaAs/Si RuO2/Ptblack was demonstrated to evolve H2 and O2 at record solar driven water electrolysis efficiency.
Abstract: Contemporary models are shown to significantly underestimate the attainable efficiency of solar energy conversion to water splitting, and experimentally a cell containing illuminated AlGaAs/Si RuO2/Ptblack is demonstrated to evolve H2 and O2 at record solar driven water electrolysis efficiency. Under illumination, bipolar configured Al0.15Ga0.85As (Eg = 1.6 eV) and Si (Eg = 1.1 eV) semiconductors generate open circuit and maximum power photopotentials of 1.30 and 1.57 V, well suited to the water electrolysis thermodynamic potential: H2O → H2 + 1/2O2; E°H2O = EO2 − EH2; E°H2O(25 °C) = 1.229 V. The E°H2O/photopotential matched semiconductors are combined with effective water electrolysis O2 or H2 electrocatalysts, RuO2 or Ptblack. The resultant solar photoelectrolysis cell drives sustained water splitting at 18.3% conversion efficiencies. Alternate dual band gap systems are calculated to be capable of attaining over 30% solar photoelectrolysis conversion efficiency.
354 citations
TL;DR: Both theory and experiment of enhanced four-wave mixing in micro-ring resonators are presented that can be used for many applications and shows a 26-dB improvement in the conversion efficiency compared with that of an equivalent straight waveguide in agreement with theory.
Abstract: Tightly confined, low-loss waveguides in highly nonlinear materials permit nonlinear optical interactions to occur over much shorter distances than do fibers The nonlinear interactions are further enhanced in resonators Both theory and experiment of enhanced four-wave mixing in micro-ring resonators are presented that can be used for many applications A conversion efficiency of 14% achievable with only 10-mW peak pump power is predicted under realizable conditions The experiment, the first one to the authors’ knowledge in nonlinear optics performed in microrings, shows, even in a lossy GaAs/AlGaAs ring, a 26-dB improvement in the conversion efficiency compared with that of an equivalent straight waveguide, in agreement with theory
311 citations
TL;DR: In this article, spin-coated bilayer thin-film heterojunctions of poly(p-phenylene vinylene) and poly(benzimidazobenzophenanthroline ladder) were found to have photovoltaic charge collection efficiency as high as 49%.
Abstract: Solar cells made from spin-coated bilayer thin-film heterojunctions of poly(p-phenylene vinylene) and poly(benzimidazobenzophenanthroline ladder) were found to have photovoltaic charge collection efficiency as high as 49%. The power conversion efficiency varied from 1.4% under sunlight illumination to 2.0% at the peak wavelength. A space-charge region around the polymer/polymer interface, Ohmic contacts at the electrodes, and complementary absorption bands of the semiconducting polymers, play important roles in the efficient charge collection in the photocells.
264 citations
TL;DR: In this paper, a soft embossing technique for printing a submicrometer grati plate was used to increase the conversion efficiency of photovoltaic devices, as is cheap and simple technology.
Abstract: Increasing the conversion efficiency is very important in photovoltaic devices, as is cheap and simple technology. Here is demonstrated a soft embossing technique for printing a submicrometer grati ...
181 citations
TL;DR: In this paper, a thin layer sandwich-type solar cell based on a 2-[4-bis(methyl)aminostyryl]benzothiazolium propylsulfonate (BTS) film was used to obtain near 100% of maximum incident photon-to-electron conversion efficiency.
171 citations
TL;DR: Thin-film devices based on doped pentacene, an organic semiconductor that has received much attention as a promising material for organic thin-film transistors, but relatively little attention for use in photovoltaic devices, appear promising for the production of efficient 'plastic’ solar cells.
Abstract: Recent work on solar cells based on interpenetrating polymer networks1,2,3 and solid-state dye-sensitized devices4 shows that efficient solar-energy conversion is possible using organic materials. Further, it has been demonstrated that the performance of photovoltaic devices based on small molecules can be effectively enhanced by doping the organic material with electron-accepting molecules5. But as inorganic solar cells show much higher efficiencies, well above 15 per cent, the practical utility of organic-based cells will require their fabrication by lower-cost techniques, ideally on flexible substrates. Here we demonstrate efficiency enhancement by molecular doping in Schottky-type photovoltaic diodes based on pentacene—an organic semiconductor that has received much attention as a promising material for organic thin-film transistors6,7,8, but relatively little attention for use in photovoltaic devices9,10. The incorporation of the dopant improves the internal quantum efficiency by more than five orders of magnitude and yields an external energy conversion efficiency as high as 2.4 per cent for a standard solar spectrum. Thin-film devices based on doped pentacene therefore appear promising for the production of efficient ‘plastic’ solar cells.
165 citations
Patent•
05 Apr 2000
TL;DR: In this paper, a photoelectric conversion device comprising an electrically conductive substrate, a photosensitive semiconductor layer, a charge transporting layer, and a counter electrode (preferably a counter- electrode having a porous electron-conducting layer), was presented.
Abstract: A photoelectric conversion device comprising an electrically conductive substrate, a photosensitive semiconductor layer, a charge transporting layer, and a counter electrode (preferably a counter electrode having a porous electron-conducting layer), wherein an electrically insulating spacing layer is provided between the semiconductor layer and the counter electrode, and a photo cell having the device. High conversion efficiency is obtained without causing an internal shortage.
120 citations
TL;DR: In this article, a two-stage solar energy concentrator with a primary one axis parabolic trough concentrator and a second stage compound parabolic concentrator mounted at the focus of the primary was designed to tolerate tracking misalignment, maintain temperature gradients to suit thermoelectric generation and minimize heat losses.
120 citations
TL;DR: In this article, a periodically poled lithium niobate crystal is used to generate narrow-band terahertz wave forms via optical rectification, and the authors obtain bandwidths as narrow as 18 GHz at a carrier frequency of 1.8 THz.
Abstract: Femtosecond optical pulses are used to generate narrow-band terahertz wave forms via optical rectification in a periodically poled lithium niobate crystal. By cooling the crystal to reduce losses due to phonon absorption, we are able to obtain bandwidths as narrow as 18 GHz at a carrier frequency of 1.8 THz. Temperature-dependent measurements show insignificant bandwidth broadening between 10 and 120 K, although the terahertz power substantially decreases as the temperature increases. Absolute power measurements indicate a conversion efficiency of at least 10−5.
TL;DR: In this article, the authors considered the detuning frequency dependence of χ(3), derived from the conversion efficiency, and showed that, within the range of detuning in the experiment, spectral-hole burning and carrier heating are responsible, and that their time constants, i.e., carrier relaxation time to the ground state and the phonon scattering time, are in the range 60 −140 and 200 −400 fs, respectively.
Abstract: Wavelength conversion using nondegenerate four-wave mixing in quantum-dot optical amplifiers is investigated. From the detuning frequency dependence of χ(3), derived from the conversion efficiency, we consider that, within the range of detuning in the experiment, spectral-hole burning and carrier heating are responsible, and that their time constants, i.e., carrier relaxation time to the ground state and the phonon scattering time, are in the range of 60–140 and 200–400 fs, respectively. This indicates that the carrier supply to the ground level via relaxation from the higher levels is very fast and that a broad conversion bandwidth comparable to that of quantum-well devices is ensured.
TL;DR: In this article, the activation energy of the charge carriers of p-MgPc/n-Si heterojunction cells was evaluated under a monochromatic illumination of 633 nm with an input power density of 50 mW/cm2.
TL;DR: A 120-W cw diode-pumped Tm:YAG laser is presented, which is side pumped by three diode arrays whose radiation is coupled through compound parabolic concentrators to achieve maximum optical-to-optical conversion efficiency.
Abstract: We present a 120-W cw diode-pumped Tm:YAG laser. The Tm:YAG rod is side pumped by three diode arrays whose radiation is coupled through compound parabolic concentrators. The maximum optical-to-optical conversion efficiency of the 2.02-mum laser output is 25.2%, with a slope efficiency of 31.2%.
Patent•
26 Jun 2000
TL;DR: In this article, an efficient, lightweight, and relatively inexpensive photolysis system based on a short-arc Hg arc lamp provides a simple and accurate method for measurement of ambient NO2.
Abstract: An efficient, lightweight, and relatively inexpensive photolysis system based on a short-arc Hg arc lamp provides a simple and accurate method for measurement of ambient NO2. High time resolution is achieved by minimizing inlet and photolysis cell residence times and matching NO and NO2 sample paths, and data reduction is greatly simplified relative to conventional photolysis designs. The single-channel embodiment includes (a) a UV light source for emitting light capable of photolytically dissociating NO2 in the gas sample to NO; (b) a device for positioning the light source; (c) an ellipsoidal reflector for collecting and focusing the light from the light source; (d) an enclosure for enclosing the light source and the ellipsoidal reflector; (e) an optical filter assembly for receiving, filtering, and transmitting the focused light; (f) a shutter capable of blocking the transmission of the filtered light which is transmitted through the optical filter assembly; (g) a sample photolysis cell for containing a volume of the gas sample; (h) a device for controllably introducing the gas sample to the sample photolysis cell, and a device for controllably delivering the gas sample from the sample photolysis cell; (i) a detector capable of detecting an amount of the NO present in the gas sample delivered from the sample photolysis cell, and capable of emitting a signal representative of the amount of NO; and (j) a device for measuring the signal so as to quantify the amount of NO. The system is characterized by i) higher conversion efficiency at faster time response; ii) lower power consumption; iii) less heat output with consequently less sample heating; iv) optically filtered light output for NO2-specific conversion, and v) simplified data reduction. The system can be used for measurement of gas-phase NO2 at concentrations ranging from parts per trillion to parts per million or higher. Present applications of the system include ambient atmospheric air measurements, while future medical applications might include the non-invasive monitoring of human breath for NO2.
TL;DR: In this paper, the current dependent barrier height has been shown to be important as a limiting factor for the energy conversion efficiency in dye sensitized injection solar cells at moderate light intensity.
Abstract: Porous TiO2 (anatase, rutile) belongs to the class of materials with very low drift mobility of electrons (10—4–10—7 cm/Vs). The drift mobility is limited by traps being responsible for the slow interparticle charge transfer. The deep traps are generated at the TiO2 surface in oxygen deficient atmosphere and should be avoided in dye sensitized injection solar cells since they increase the saturation current. Another group of defects is related to disorder in the bulk TiO2. The disorder is much stronger for anatase than for rutile. The respective optical bandgap of the undisturbed anatase is 3.45 eV. The disorder related defects do not limit the efficiency of the dye sensitized injection solar cell. The current dependent barrier height has been shown to be important as a limiting factor for the energy conversion efficiency in dye sensitized injection solar cells at moderate light intensity.
15 Nov 2000-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the possibility of engineering the phonon transport in nanostructures, with emphases on the thermal conductivity of superlattices, was discussed and compared with recent experimental studies to illustrate the potential approaches and remaining questions.
Abstract: Solid-state energy conversion technologies such as thermoelectric and thermionic refrigeration and power generation require materials with low thermal conductivity but good electrical conductivity, which are difficult to realize in bulk semiconductors. Nanostructures such as quantum wires and quantum wells provide alternative approaches to improve the solid-state energy conversion efficiency through size effects on the electron and phonon transport. In this paper, we discuss the possibility of engineering the phonon transport in nanostructures, with emphases on the thermal conductivity of superlattices. Following a general discussion on the directions for reducing the lattice thermal conductivity in nanostructures, specific modeling results on the phonon transport in superlattices will be presented and compared with recent experimental studies to illustrate the potential approaches and remaining questions.
TL;DR: In this article, a comparative analysis is made of laser diodes based on Stranski-Krastanow (SK) and sub-monolayer (SML) InAs/GaAs quantum dots, emitting at about 940nm.
Abstract: A comparative analysis is made of laser diodes based on Stranski-Krastanow (SK) and sub-monolayer (SML) InAs/GaAs quantum dots, emitting at about 940 nm. Owing to the better uniformity of sub-monolayer quantum dots, the SML QD laser surpasses the SK QD one in power characteristics. A maximum output power of 3.9 W and a peak power conversion efficiency of 59% have been achieved for SML QD 100 µm wide lasers at 10 °C.
Patent•
17 May 2000TL;DR: In this paper, a transparent substrate, a transparent conductive film, photoelectric conversion units, and a back electrode are stacked sequentially from a side on which light is incident.
Abstract: A transparent substrate, a transparent conductive film, photoelectric conversion units, and a back electrode are stacked sequentially from a side on which light is incident. Further, intermediate films are formed between the transparent substrate and the transparent conductive film. The intermediate films are formed so that the relationship of R 1
TL;DR: In this article, a circularly polarised rectenna using a truncated-corner square-patch microstrip antenna has been developed for wireless power transmission at 5.8 GHz.
Abstract: A circularly polarised rectenna using a truncated-corner square-patch microstrip antenna has been developed for wireless power transmission at 5.8 GHz. The gain and axial ratio achieved were 8.5 dBi and 0.5 dB at 5.82 GHz respectively. A GaAs Schottky barrier diode was employed for microwave to DC conversion with a maximum conversion efficiency of 60%.
TL;DR: In this paper, a three-layer solar cell Al/PV/HD/MC/Au showed fairly good photovoltaic properties, short-circuit photocurrent quantum yield of 49.2%, opencircuit photvoltage of 0.39 V, and energy conversion yield of 3.51% when irradiated with 445 nm monochromatic light.
TL;DR: In this article, a self-frequency-doubled green laser output of 160 mW was obtained from Yb:YAl3BO34 crystal pumped by 1.4 W incident power from a fiber-coupled 976-nm laser diode.
Abstract: Efficient cw self-frequency-doubled green laser output of 160 mW has been obtained from Yb:YAl3BO34 crystal pumped by 1.4-W incident power from a fiber-coupled 976-nm laser diode. The incident-pump-power–green-output-power conversion efficiency is greater than 11.3%, and the electrical-input–green conversion efficiency is 3.9%. Tunable green output from 513.0 to 545.8 nm is also demonstrated with a quartz birefringent filter.
TL;DR: A novel traveling-wave-type optical parametric generator based on 1.25-microm pumping of HgGa(2)S(4) that produces tunable, high-power, transform-limited infinity 200-fs pulses in the mid-IR from 5 to 9 microm is demonstrated.
Abstract: We demonstrate a novel traveling-wave-type optical parametric generator based on 1.25‐µm pumping of HgGa2S4 that produces tunable, high-power, transform-limited ∝200‐fs pulses in the mid-IR from 5 to 9 µm. Output idler energies on the microjoule level are obtained with maximum conversion efficiency of 11% for the amplifier stage, which is more than two times better than the results obtained with an analogous sample of the widely spread material AgGaS2.
TL;DR: In this article, a medium-power Autonomous Renewable Energy Conversion System (ARECS), integrating conversion of wind and solar energy sources, is proposed to extract maximum power from the proposed wind energy conversion scheme and to transfer this power and the power derived by the photovoltaic system in a high efficiency way to a local isolated load.
TL;DR: The use of photovoltaic solar cells provides an elegant way of converting sunlight to electricity as discussed by the authors, and low-dimensional structures appear capable of allowing much of this gap to be bridged.
Abstract: The use of photovoltaic solar cells provides an elegant way of converting sunlight to electricity. The photovoltaic industry is currently growing very rapidly, at a compounded rate of about 30% each year. Energy conversion efficiency is a key parameter with this technology since it directly impacts both material and deployment costs. The performance of the traditional bulk semiconductor solar cell is limited to about 33% while thermodynamic limits on the conversion of sunlight to electricity are much higher, at 93%. Low-dimensional structures appear capable of allowing much of this gap to be bridged. These structures allow increased flexibility with traditional efficiency enhancement approaches such as those based on `stacked' or tandem cells, which double efficiency limits to 68%. Perhaps more interestingly, they offer scope for completely new device concepts such as those relying on excitations between multiple energy bands and improved `hot-carrier' cells, that offer scope for similarly high performance.
TL;DR: In this paper, a fluorescent plate was used as a protecting plate for the solar cell module, and the effect of the coloration on the energy conversion efficiency was discussed on the basis of a simple model for the absorption and re-emission of light in the fluorescent plate and spectral reflection of the solar cells.
TL;DR: In this article, a self-frequency doubling of Nd:GdCOB crystal by type-I phase-matching at θ=66.3° and ϕ=134.4° was reported.
TL;DR: In this paper, the electron beam radio frequency (RF) field interaction of the monotron, which is the simplest transit-time microwave tube, was examined and it was found that a 20% maximum conversion efficiency can be attained at weakly relativistic beam energies (/spl sim/200 keV).
Abstract: Upon reexamining the electron beam radio frequency (RF)-field interaction of the monotron, which is the simplest transit-time microwave tube, it is found that a 20% maximum conversion efficiency can be attained at weakly relativistic beam energies (/spl sim/200 keV). It is shown that the conversion efficiency can be cast as a function of three parameters, namely, injection beam energy, resonant frequency, and electric field strength. From this fact, a design procedure of how the optimum operating parameters should be selected is presented. In support of the analytic study, 2.5-D particle-in-cell simulation of a transverse magnetic (TM)/sub 020/, 6.7 GHz axial monotron operating at 10 keV, 70 A beam parameters has given a tube efficiency of 15.4%, while one-dimensional (1-D) analysis assuming a strictly monoenergetic beam has predicted a maximum theoretical efficiency of 18.5% at a beam energy of 10 keV.
TL;DR: In this article, a diode-laser-array end-pumped intracavity frequency-doubled Nd:GdVO 4 /KTP green laser, formed with a three-mirror folded cavity, and capable of generating 3.6 W of CW green radiation with optical conversion efficiency of 22.5%, has been demonstrated.
TL;DR: In this paper, a near-diffraction-limited-beam continuous-wave (cw) operation has been achieved to high powers from antiguided arrays with a large effective-index step between element and interelement regions.
Abstract: Near-diffraction-limited-beam continuous-wave (cw) operation has been achieved to high powers from antiguided arrays with a large effective-index step between element and interelement regions. InGaAs/InGa(As)P/GaAs 40-element arrays (λ=0.985 μm) emit in beams 2×diffraction-limit (0.67°) at 1.6 W and 9×threshold in cw operation. 1 W of the coherent cw power resides in the central lobe. The external differential quantum efficiency and the threshold current are 40% and 0.4 A, respectively, for 1-mm-long devices of 191 μm emitting aperture. The overall electrical to optical power conversion efficiency at 1.6 W output power is 23%. Modeling of the thermal effects in cw operation on the array modes reveals that for high-index-step (∼0.1) near-resonant antiguided arrays thermal lensing hardly affects high-order modes, and as a consequence, 2×diffraction-limited beams can be maintained to watt-range cw powers.