Showing papers on "Energy conversion efficiency published in 1998"

Solid-state dye-sensitized mesoporous TiO2 solar cells with high photon-to-electron conversion efficiencies

Abstract: Solar cells based on dye-sensitized mesoporous films of TiO2 arelow-cost alternatives to conventional solid-state devices1. Impressive solar-to-electrical energy conversion efficiencies have been achieved with such films when used in conjunction with liquid electrolytes2. Practical advantages may be gained by the replacement of the liquid electrolyte with a solid charge-transport material. Inorganic p-type semiconductors3,4 and organic materials5,6,7,8,9 have been tested in this regard, but in all cases the incident monochromatic photon-to-electron conversion efficiency remained low. Here we describe a dye-sensitized heterojunction of TiO2 with the amorphous organic hole-transport material 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (OMeTAD; refs. 10 and 11). Photoinduced charge-carrier generation at the heterojunction is very efficient. A solar cell based on OMeTAD converts photons to electric current with a high yield of 33%.

Laminated fabrication of polymeric photovoltaic diodes

Abstract: Photoexcited electron transfer between donor and acceptor molecular semiconductors provides a method of efficient charge generation following photoabsorption, which can be exploited in photovoltaic diodes1,2,3 But efficient charge separation and transport to collection electrodes is problematic, because the absorbed photons must be close to the donor–acceptor heterojunction, while at the same time good connectivity of the donor and acceptor materials to their respective electrodes is required Mixtures of acceptor and donor semiconducting polymers3,4 (or macromolecules5) can provide phase-separated structures which go some way to meeting this requirement, providing high photoconductive efficiencies Here we describe two-layer polymer diodes, fabricated by a lamination technique followed by controlled annealing The resulting structures provide good connectivity to the collection electrodes, and we achieve a short-circuit photovoltaic quantum efficiency of up to 29% at optimum wavelength, and an overall power conversion efficiency of 19% under a simulated solar spectrum Given the convenience of polymer processing, these results indicate a promising avenue towards practical applications for such devices

Design and experiments of a high-conversion-efficiency 5.8-GHz rectenna

Abstract: A high-efficiency rectenna element has been designed and tested at 5.8 GHz for applications involving microwave-power transmission. The dipole antenna and filtering circuitry are printed on a thin duroid substrate. A silicon Schottky-barrier mixer diode with a low breakdown voltage is used as the rectifying device. The rectenna element is tested inside a waveguide simulator and achieves an RF-to-DC conversion efficiency of 82% at an input power level of 50 mW and 327 /spl Omega/ load. Closed-form equations are given for the diode efficiency and input impedance as a function of input RF power. Measured and calculated efficiency results are in good agreement. The antenna and circuit design are based on a full-wave electromagnetic simulator. Second harmonic power levels are 21 dB down from the fundamental input power.

1.5-microm-band wavelength conversion based on difference-frequency generation in LiNbO3 waveguides with integrated coupling structures.

Abstract: We report wavelength conversion within the 1.5?µm telecommunications band based on difference-frequency generation in periodically poled lithium niobate waveguides with integrated coupling structures. A conversion efficiency of -7 dB and a normalized efficiency of 260%/W are demonstrated. Static tests show that the conversion bandwidth is 72 nm and the conversion efficiency is constant over the 20-dB range of input powers tested.

Switched-mode high-efficiency microwave power amplifiers in a free-space power-combiner array

Abstract: A design-oriented analysis of the microwave transmission-line class-E amplifier is presented. Experiments and harmonic-balance circuit simulations verify the theoretical equations which predict class-E-amplifier output power, maximum frequency of operation, and dc-RF conversion efficiency. Experimental results at 0.5, 1,2, and 5 GHz are presented. At 0.5 GHz, 83% drain efficiency and 80% power-added efficiency (PAE) are measured, with an output power of 0.55 W, using the Siemens CLY5 MESFET. These results are compared to a class-A and class-F power amplifier using the same device. At 5 GHz, 81% drain efficiency and 72% PAE are measured, with an output power of 0.61 W, using the Fujitsu FLK052WG MESFET. Finally, the 5-GHz class-E power amplifier is successfully integrated into an active-antenna array, demonstrating power combining of four elements with an 85% power-combining efficiency. At 5.05 GHz, the class-E power-amplifier antenna array delivers a total of 2.4 W of output power, with a dc-RF conversion efficiency of 74% and a PAE of 64%.

Design and Experiments of a High-Conversion-Efficiency

Abstract: A high-efficiency rectenna element has been designed and tested at 5.8 GHz for applications involving microwave- power transmission. The dipole antenna and filtering circuitry are printed on a thin duroid substrate. A silicon Schottky- barrier mixer diode with a low breakdown voltage is used as the rectifying device. The rectenna element is tested inside a waveguide simulator and achieves an RF-to-dc conversion efficiency of 82% at an input power level of 50-mW and 327- load. Closed-form equations are given for the diode efficiency and input impedance as a function of input RF power. Measured and calculated efficiency results are in good agreement. The antenna and circuit design are based on a full-wave electromagnetic simulator. Second harmonic power levels are 21 dB down from the fundamental input power.

Solar cell efficiency and carrier multiplication in Si1−xGex alloys

Abstract: Crystalline Si1−xGex compounds offer the possibility for tuning the electronic energy band structure with the chemical composition of the alloy in order to adapt the material for devices utilizing the energy of solar photons at an optimum. We concentrate on the efficiency enhancement due to carrier multiplication by impact ionization. We calculate the internal quantum efficiency and the possible solar cell efficiency for this material system. The number of impact-generated charge carriers is obtained by a simulation of the competing carrier–carrier and carrier–photon scattering processes. These calculations show that the wave vector dependence of the scattering processes is unimportant for good agreement between theoretical and experimental quantum efficiencies in Si and Ge. Finally, we calculate solar cell efficiencies under the ideal assumption of unity collection efficiency and radiative recombination only. Impact ionization enhances the theoretical conversion efficiency by 0.5 percentage point; this i...

Minority-carrier lifetime and efficiency of Cu(In,Ga)Se2 solar cells

Abstract: Room-temperature recombination dynamics has been investigated in a large set of different Cu(In,Ga)Se2 absorber films and compared to the electrical device characteristics of the respective solar cell modules. For a given cell preparation process, a characteristic relation between the low-injection minority-carrier lifetime of the absorber layers and the conversion efficiency of the solar cells is observed: Long lifetimes correlate with high open circuit voltages and conversion efficiencies, while no significant influence of the lifetime on the short circuit current is found.

Color conversion material, and organic electroluminescent color display using the same

Abstract: A color conversion material comprises a high-molecular material having a light transmittance of at least 90% in a visible light region, a fluorescent dye contained therein, and a fluorescent pigment particle dispersed therein. The wavelength of unconverted light incident on the color conversion material is up to 520 nm, the light emission maximum wavelength of the conversion material is at least 580 nm upon incident light conversion, and the conversion efficiency of at least 10% is obtained.

Bottom-emitting VCSEL's for high-CW optical output power

Abstract: Bottom-emitting vertical-cavity surface-emitting InGaAs MQW lasers operating in the 980-nm wavelength regime have been designed for high continuous-wave optical output power. Devices of 200-/spl mu/m active diameter and optimized performance reach 350-mW maximum output power when mounted on a heat sink. 50-/spl mu/m-size lasers produce 100 mW at 25% electrical to optical power conversion efficiency. Thermal properties and size dependent basic characteristics are investigated in detail.

Low-power high-efficiency wavelength conversion based on modulational instability in high-nonlinearity fiber.

Abstract: Bandwidth and peak efficiency are enhanced for wavelength conversion based on induced modulation instability by use of dispersion-shifted fiber in which the nonlinearity n2/Aeff is enhanced by a factor of ?4.5 over that of conventional dispersion-shifted fiber. We experimentally obtain a peak conversion efficiency as high as 28??dB over a 40-nm bandwidth with 600??mW of peak pump power. Considerations for further enhancement of fiber-based wavelength conversion are also discussed.

Modulation instability wavelength converter

Abstract: Disclosed is an all waveguide fiber wavelength converter which makes use of modulational instability to convert signal wavelength over a conversion bandwidth while maintaining a low pump laser power relative to other wavelength conversion devices such as those which make use of four wave mixing. The device is operated in the anomalous dispersion regions of the waveguides and the zero dispersion of the waveguide in which conversion occurs is less than the pump wavelength so that conversion may occur for signal wavelengths above and below the zero dispersion wavelength. Conversion efficiency is in the range of 25 dB to 30 dB.

Effects of self-heating on planar heterostructure barrier varactor diodes

Abstract: The conversion efficiency for planar Al/sub 0.7/GaAs-GaAs heterostructure barrier varactor triplers is shown to be reduced from a theoretical efficiency of 10% to 3% due to self-heating. The reduction is in accordance with measurements on planar Al/sub 0.7/GaAs-GaAs heterostructure barrier varactor (HBV) triplers to 261 GHz at room temperature and with low temperature tripler measurements to 255 GHz. The delivered maximum output power at 261 GHz is 2.0 mW. Future HBV designs should carefully consider and reduce the device thermal resistance and parasitic series resistance. Optimization of the RF circuit for a 10 /spl mu/m diameter device yielded a delivered output power of 3.6 mW (2.5% conversion efficiency) at 234 GHz.

Efficient XeI* excimer ultraviolet sources from a dielectric barrier discharge

Abstract: A dielectric barrier discharge in mixtures of xenon and iodine to provide intense narrow band ultraviolet (UV) radiation at λ=253 nm (XeI*) has been investigated. The characteristics of the emission spectra of the excited dimer (excimer) and UV intensity formed from mixtures of xenon and iodine for different total gas pressures are reported. The absolute UV output power of the XeI* lamp has been determined using actinometry based on the photohydrate of uridine. The electrical power dependence of the UV intensity generated as well as the conversion efficiency of the lamps has also been studied. Conversion efficiencies (from input electrical to output optical energy) as high as 22.5% have been achieved for an electrical power input of 70 W, with 15.75 W of optical output being generated.

Semiconductor light-emitting element, semiconductor light-emitting device, and image-display device

Abstract: PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element and device that has an extremely stable emission wavelength and is able to convert the wavelength with a high conversion efficiency in various kinds of wavelengths from visible light to infrared regions. SOLUTION: A wavelength conversion part FL with a wavelength conversion function and a light-reflecting part RF1 with wavelength selectivity properly combine a light-absorbing part AB with wavelength selectivity and appropriately arranges it in a specific relationship, thus breaking the leakage of primary light toward the outside and at the same time, converting the wavelength with extremely high efficiency and taking out secondary light.

16-microm infrared generation by difference-frequency mixing in diffusion-bonded-stacked GaAs

Abstract: Tunable 90-ps 15.6–17.6?µm coherent radiation was generated by means of difference-frequency mixing in diffusion-bonded-stacked GaAs. The sample consisted of 24 alternately rotated layers with a total length of 6 mm and with low optical loss to achieve third-order quasi-phase matching. The wavelength-tuning curve was close to the theoretical prediction, demonstrating that the bonding process maintained nonlinear optical phase matching over the entire interaction length. Maximum conversion efficiency of 0.7%, or 5% internal quantum efficiency, was measured at 16.6 µm, consistent with the theoretical predictions.

Backward second-harmonic generation in periodically poled lithium niobate

Abstract: For periodically poled LiNbO3 with a 3.3-μm domain period we observed backward second-harmonic generation using nanosecond laser pulses. We measured phase-matching spectra at the 16th, 17th, 18th, 19th, and 20th orders of the spatial grating. The peak wavelength of each order is in good agreement with the theoretical prediction. The quadratic dependence of the backward second-harmonic output pulse energy on the pump pulse energy was confirmed in our experiments. The quadratic dependence of the conversion efficiency on the domain length was also confirmed. Using nanosecond pulses, we achieved a maximum conversion efficiency of 0.296% for the 16th-order grating.

Highly efficient second-harmonic and sum-frequency generation of nanosecond pulses in a cascaded erbium-doped fiber:periodically poled lithium niobate source.

Abstract: Recently, femtosecond erbium fibre lasers have been used with periodically poled lithium niobate(PPLN) to demonstrate frequency doubling with up to 25% conversion efficiency, and using the second harmonic, to pump an Optical Parametric Generator (OPG). However, for many applications e.g. pumping of nanosecond Optical Parametric Oscillators (OPOs) pulses with greater energies are required, for which diode-pumped, large mode-area erbium doped fibre amplifiers (LA-EDFA) and lasers are ideally suited. The combination of diode-pumped, LA-EDFA sources with periodically poled lithium niobate creates an extremely attractive technology for the development of a wide range of practical wavelength tuneable sources. In this work both diode-seeded LA-EDFA chains and Q-switched sources were used to demonstrate extremely high second and third harmonic single pass conversion efficiencies in PPLN. Continuously tunable operation over the erbium gain bandwidth was demonstrated with pulses from 2 to 50ns, repetition rates from 1kHz to 150kHz, and pulse energies of up to 50µJ. Output pulses at a fundamental wavelength of 1536nm were frequency doubled in PPLN, to produce 768nm light with internal conversion efficiencies as high as 83% in a single pass for a peak power of 1.2kW. A second PPLN crystal was used to mix the second harmonic with the remaining fundamental to generate green light at 512nm, with up to 34% internal conversion efficiency. Both PPLN samples were 16mm long and fabricated in 0.5mm thick z-cut lithium niobate by electrical poling. The periods were 18.05µm for SHG and 6.5µm for sum frequency generation.

Widely tunable four-wave mixing in semiconductor optical amplifiers with constant conversion efficiency

Abstract: The conversion efficiency and output signal-to-noise ratio (SNR) of single-pump four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is strongly dependent on frequency shift. We examine a scheme for FWM in SOAs that uses two orthogonally polarized pumps. We compare experimentally and theoretically the conversion efficiency and SNR of the orthogonal-pump scheme with single-pump FWM. The orthogonal-pump scheme has nearly constant conversion efficiency and SNR over the 4.5-THz range of frequency shifts measured. Experimental and theoretical results for the conversion efficiency and SNR of the orthogonal-pump scheme agree to within 3.5 dB.

Characterization of photovoltaic cells using poly(phenylenevinylene) doped with perylenediimide electron acceptors

Abstract: The performance of a sandwich junction device based on doped 1,4-bis(2-ethylhexyloxy)phenylenevinylene (BEH-PPV) is reported. The power conversion efficiency is dependent on the doping level, external load, and work function of the cathode. The increase in power conversion efficiency (ηe=0.8%) is due to efficient charge separation resulting from photoinduced electron transfer from the BEH-PPV donor to the perylene dicarboximide acceptor.

Waveguide second-harmonic generation device with broadened flat quasi-phase-matching response by use of a grating structure with located phase shifts.

Abstract: We report on a theoretical analysis and experiments for bandwidth broadening in quasi-phase-matched (QPM) second-harmonic generation (SHG). We used phase-shifted segments of a periodic grating to obtain a spectrally broadened, nearly flat response simultaneously with high conversion efficiency. We used an x-cut MgO:LiNbO3 QPM waveguide in our analysis and experiments. The spectral range of the 850-nm fundamental for which SHG conversion exceeded 0.95 of the maximum value broadened from 0.02 to 0.12 nm when a 1-cm-long grating was divided into three segments with optimum phase shift. SHG conversion efficiency was 300%/W for this waveguide. The SHG efficiency and phase-matching characteristics showed good agreement with theoretical results.

Narrowband laser produced extreme ultraviolet sources adapted to silicon/molybdenum multilayer optics

Abstract: The extreme ultraviolet radiation emitted from a plasma generated by a pulsed Nd:yttrium aluminum garnet laser is investigated around 13 nm wavelength for several low Z elements (lithium, nitrogen, oxygen, fluorine). A narrowband EUV source can be designed by using the narrowband line emission of low Z elements in combination with the broadband reflection characteristic of silicon/molybdenum (Si/Mo) multilayer mirrors. Experimental results are discussed within a theoretical model, which allows a deduction of an optimization criterion for a maximum conversion efficiency. The Lyman-α line of hydrogenlike lithium ions fulfills the demands for high intense, free-standing narrowband emission at the long wavelength side of the silicon absorption L edge.

Vacuum ultraviolet application of Li2B4O7 crystals: Generation of 100 fs pulses down to 170 nm

Abstract: We investigate and characterize the newly grown crystal Li2B4O7 which is transparent down to 160 nm for nonlinear optical conversion into the vacuum ultraviolet using sum frequency mixing with femtosecond pulses. This material exhibits excellent properties below 180 nm and makes possible the generation of wavelengths down to 170 nm with an all solid state laser system. The most important advantage of Li2B4O7 in this spectral range turns out to be the possibility of utilizing noncritical phase matching with maximized effective nonlinearity. We demonstrate generation of nearly transform limited 100 fs pulses between 170 and 185 nm with conversion efficiency of 4%. Their peak powers range from 200 kW at 170 nm to >2 MW at 185 nm.

Efficient Nd:YAG laser frequency doubling with periodically poled KTP

Abstract: Periodically poled flux-grown KTiOPO(4) was used for efficient extracavity 1064-nm Nd:YAG laser frequency doubling A conversion efficiency exceeding 65% was obtained in Q-switched operation, and 134 W of average frequency-doubled power was generated with 22 W of mode-locked laser output The conversion efficiency is approximately two times higher for periodically poled KTP than for conventional type II phase-matched KTP The measurements indicate that periodically poled KTP is less susceptible to optical damage than type II KTP

Increased efficiency of silicon light-emitting diodes in a standard 1.2-μm silicon complementary metal oxide semiconductor technology

Abstract: Scaled versions of a variety of silicon light-emitting diode elements (Si LEDs) have been realized using a standard 1.2-µm, doublepolysilicon, double-metal, n-well CMOS fabrication process. The devices operated with a n+p junction biased in the avalanche breakdown mode and were realized by using standard features of the ORBIT FORESIGHT design rules. The elements emit optical radiation in a broad band in the 450- to 850-nm range. An emitted intensity (radiant exitance) of up to 7.1 µW/cm2 (or about 8 nW per 60-µm-diam chip area) has been obtained with 5 mA of current at an operating voltage of 18.5 V. Excellent uniformity in emission intensity of better than 1% variation was obtained over areas as large as 100x500 µm. A best power conversion efficiency of 8.7x 10-8 and a quantum efficiency of 7.8x 10-7 were measured. All of these values are about one order of magnitude better than previously reported values for Si LED avalanche devices. Coupling between the elements as well as electro-optical coupling between an element and an optical fiber was realized.

Femtosecond stimulated Raman scattering in pressurized gases in the ultraviolet and visible spectral ranges

Abstract: We investigate femtosecond stimulated Raman scattering (SRS) in H2,D2, HD, and CH4 excited with 300-fs-duration pulses at 390-nm wavelength and with as much as 0.1 mJ of energy. We show that the SRS-generation threshold and conversion efficiency are due to the transient nature of SRS in femtosecond regime. We determine optimal conditions for efficient generation in the broad spectral range 289–797 nm and show how self-phase modulation and white-light generation limit the ultimate conversion efficiency.