Showing papers on "Energy conversion efficiency published in 2003"
TL;DR: In this paper, the double heterojunction was proposed to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved, and a full optical and electrical analysis of the double-heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials.
Abstract: In this review, we discuss the physics underlying the operation of single and multiple heterojunction, vacuum-deposited organic solar cells based on small molecular weight thin films. For single heterojunction cells, we find that the need for direct contact between the deposited electrode and the active organics leads to quenching of excitons. An improved device architecture, the double heterojunction, is shown to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved. A full optical and electrical analysis of the double heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials. Combining the double heterostructure with novel light trapping schemes, devices with external efficiencies approaching their internal efficiency are obtained. When applied to an organic photovoltaic cell with a power conversion efficiency of 1.0%±0.1% under 1 sun AM1.5 illuminati...
2,722 citations
TL;DR: This method results in a power conversion efficiency 50 per cent higher than the best values reported for comparable bilayer devices, suggesting that this strained annealing process could allow for the formation of low-cost and high-efficiency thin film organic solar cells based on vacuum-deposited small-molecular-weight organic materials.
Abstract: The power conversion efficiency of small-molecular-weight and polymer organic photovoltaic cells has increased steadily over the past decade This progress is chiefly attributable to the introduction of the donor–acceptor heterojunction1,2 that functions as a dissociation site for the strongly bound photogenerated excitons Further progress was realized in polymer devices through use of blends of the donor and acceptor materials3,4,5: phase separation during spin-coating leads to a bulk heterojunction that removes the exciton diffusion bottleneck by creating an interpenetrating network of the donor and acceptor materials The realization of bulk heterojunctions using mixtures of vacuum-deposited small-molecular-weight materials has, on the other hand, posed elusive: phase separation induced by elevating the substrate temperature inevitably leads to a significant roughening of the film surface and to short-circuited devices Here, we demonstrate that the use of a metal cap to confine the organic materials during annealing prevents the formation of a rough surface morphology while allowing for the formation of an interpenetrating donor–acceptor network This method results in a power conversion efficiency 50 per cent higher than the best values reported for comparable bilayer devices, suggesting that this strained annealing process could allow for the formation of low-cost and high-efficiency thin film organic solar cells based on vacuum-deposited small-molecular-weight organic materials
1,306 citations
TL;DR: A new powerful tool to study the electron lifetime in dye solar cells as a function of the photovoltage (Voc) ; the open-circuit voltage-decay (OCVD) technique is developed and has certain advantages over frequenIn summary, the temperature effect on the arrangement of stilbenoid dendrimers on HOPG is presented in this work.
Abstract: Recently, a new class of photoelectrochemical cells based on nanoscaled porous metal oxide semiconductors (dye-sensitized solar cell) has promoted intense research due to the prospects of cheap and efficient conversion of visible light into electricity and of new applications such as transparent solar cells. It is widely agreed that the electron-transfer kinetics play a major role in determining the energy conversion efficiency of dye-sensitized solar cells. 3] Herein, we develop a new powerful tool to study the electron lifetime in dye solar cells as a function of the photovoltage (Voc) ; the open-circuit voltage-decay (OCVD) technique. This technique has certain advantages over frequenIn summary, the temperature effect on the arrangement of stilbenoid dendrimers on HOPG is presented in this work. It is seen that SD12 molecules form well-ordered hexagonal nanostructures at 16 C. However, if the adlayer is annealed at 65 C, the adlayer structure is changed into a well-ordered parallelogram nanostructure in a close-packed arrangement with a higher surface coverage. The phenomenon described here supports the earlier reports on two liquid-crystalline phases for SD12. The results in this research are useful in understanding the phase transition of SD12 as well as metastable complex systems with temperature.
1,156 citations
TL;DR: In this paper, the influence of temperature and wavelength on electrical parameters of crystalline silicon solar cells and a solar module is presented, and the spectral characteristic of the open-circuit voltage of the single-crystalline silicon polysilicon solar cell is also presented.
473 citations
TL;DR: In this article, a three-dimensional tungsten photonic crystal is realized with a complete photonic band gap at wavelengths λ⩾3 μm, and an optical-to-electric conversion efficiency of ∼34% and electrical power of ∼14 W/cm2 is theoretically possible.
Abstract: A three-dimensional tungsten photonic crystal is experimentally realized with a complete photonic band gap at wavelengths λ⩾3 μm. At an effective temperature of 〈T〉∼1535 K, the photonic crystal exhibits a sharp emission at λ∼1.5 μm and is promising for thermal photovoltaic (TPV) power generation. Based on the spectral radiance, a proper length scaling and a planar TPV model calculation, an optical-to-electric conversion efficiency of ∼34% and electrical power of ∼14 W/cm2 is theoretically possible.
392 citations
TL;DR: An efficient and novel polyene-dye-sensitized nanocrystalline TiO2 solar cells producing a 6.8% solar energy-to-electricity conversion efficiency under AM 1.5 irradiation is developed.
280 citations
TL;DR: In this article, the effect of electron recirculation on the rear side sheath acceleration is discussed and it is found that the peak proton energy increases in inverse proportion to the target thickness.
Abstract: The generation of high energy protons from the interaction of a short laser pulse with a dense plasma, accompanied by a preformed low density plasma, has been studied by particle-in-cell simulations. The proton acceleration toward the laser direction in the preformed plasma is characterized by a time-dependent model and the peak proton energy is given. The effect of electron recirculation on the rear side sheath acceleration is discussed and it is found that the peak proton energy increases in inverse proportion to the target thickness. These results shed light on the peak proton energy dependence on laser intensity, laser pulse length, and target thickness. Finally the optimal parameters of the laser pulse for large ion peak energy and conversion efficiency are discussed.
258 citations
TL;DR: In this paper, a modulated hollow-core waveguide is used to periodically vary the intensity of the laser light driving the conversion, which can be used to generate high-energy extreme-ultraviolet (EUV) light.
Abstract: High-harmonic generation is a well-known method of producing coherent extreme-ultraviolet (EUV) light, with photon energies up to about 0.5 keV (refs 1, 2). This is achieved by focusing a femtosecond laser into a gas, and high harmonics of the fundamental laser frequency are radiated in the forward direction. However, although this process can generate high-energy photons, efficient high-harmonic generation has been demonstrated only for photon energies of the order 50-100 eV (ref. 5). Ionization of the gas prevents the laser and the EUV light from propagating at the same speed, which severely limits the conversion efficiency. Here we report a technique to overcome this problem, and demonstrate quasi-phase-matched frequency conversion of laser light into EUV. Using a modulated hollow-core waveguide to periodically vary the intensity of the laser light driving the conversion, we efficiently generate EUV light even in the presence of substantial ionization. The use of a modulated fibre shifts the energy spectrum of the high-harmonic light to significantly higher photon energies than would otherwise be possible. We expect that this technique could form the basis of coherent EUV sources for advanced lithography and high-resolution imaging applications. In future work, it might also be possible to generate isolated attosecond pulses.
256 citations
TL;DR: For the first time highest power conversion efficiencies are obtained for dye sensitized solar cells using a swift self-assembled procedure.
201 citations
TL;DR: This work demonstrates an approximately 10x increase in conversion efficiency for optical second-harmonic generation from a periodically nanostructured metal structure consisting of a single subwavelength aperture in a thin silver film surrounded by a set of concentric surface grooves.
Abstract: We demonstrate an ∼104 increase in conversion efficiency for optical second-harmonic generation (SHG) from a periodically nanostructured metal structure consisting of a single subwavelength aperture in a thin silver film surrounded by a set of concentric surface grooves. The forward-transmitted second-harmonic radiation from this structure is measured relative to that from an identical aperture with no surrounding surface periodicity. We explain the observed SHG enhancement quantitatively in terms of a measured 120× increase in the strength of the fundamental radiation in the vicinity of the aperture resulting from the periodic nanostructuring.
191 citations
TL;DR: In this paper, the experimental demonstration of second-harmonic generation in periodically poled GaN by first-order quasiphase matching was reported, with a normalized conversion efficiency of 12.76% W−1 cm−2.
Abstract: We report the experimental demonstration of second-harmonic generation in periodically poled GaN by first-order quasiphase matching. The periodically poled structure was grown by plasma-assisted molecular-beam epitaxy. We observed about 9 μW of second-harmonic power from a fundamental input laser wavelength of 1658.6 nm with a normalized conversion efficiency of 12.76% W−1 cm−2. The ability to perform nonlinear wavelength conversion by periodic poling and the fact that GaN has a very wide window of transparency, pave the way for GaN to be used for nonlinear optical devices in telecommunications as well as a nonlinear light source for biochemical detection in the far infrared and deep ultraviolet.
TL;DR: The first observation of parametric down-conversion in silicon is reported and it is shown that the power conversion efficiency is a strong function of phase mismatch inside the waveguide.
Abstract: The first observation of parametric down-conversion in silicon is reported. Conversion from 1542.3nm to 1328.8nm is achieved using a CW pump laser at 1427 nm. The conversion occurs via Coherent Anti-Stokes Raman Scattering (CARS) in which two pump photons and one Stokes photon couple through a zone-center optical phonon to an anti-Stokes photon. The maximum measured Stokes/anti-Stokes power conversion efficiency is 1×10-5. The value depends on the effective pump power, the Stimulated Raman Scattering (SRS) coefficient of bulk silicon, and waveguide dispersion. It is shown that the power conversion efficiency is a strong function of phase mismatch inside the waveguide.
TL;DR: In this article, the authors demonstrate more than 8-W continuous-wave output power with good beam quality (M2 < 1.8) from an optically pumped semiconductor disk laser.
Abstract: We demonstrate more than 8-W continuous-wave output power with good beam quality (M2<1.8) from an optically pumped semiconductor disk laser. The combination of low threshold density of 470 W/cm2 and high differential efficiency of 60% results in an optical-to-optical conversion efficiency of 46% for this high output level. Good epitaxial quality and low thermal resistance allow the scaling of output power with pump spot area.
TL;DR: Carboxylated polythiophenes were found to be alternative photo sensitizers for nanocrystalline TiO2 photovoltaic (PV) cells as mentioned in this paper.
Abstract: Carboxylated polythiophenes were found to be alternative photo sensitizers for nanocrystalline TiO2 photovoltaic (PV) cells. The overall solar-to-electric energy conversion efficiency found was ∼1.5% in these regenerative electrochemical photovoltaic cells without any dye sensitizer. These initial and promising results are believed to be due to the presence of the carboxylic group which provides enhanced adsorption and transport of the photoinduced charge. Further optimization is expected to result in even higher PV performance.
TL;DR: In this article, the effectiveness of a hybrid solar collector that generates both electric power and heat was described and compared to those of a photovoltaic and a solar collector, and it was clarified that the hybrid collector had an advantage in terms of exergy efficiency, though there is some lowering of collector efficiency.
TL;DR: In this article, the authors discuss the specific design considerations for high solar-to-hydrogen conversion efficiency in a hybrid solid-state/PEC photoelectrode, and describe the use of integrated electrical/electrochemical/optical models developed at the University of Hawaii for the analysis of such hybrid structures.
TL;DR: To the authors' knowledge this is the highest conversion efficiency and stability achieved in an optical parametric chirped-pulse amplification system.
Abstract: High-conversion-efficiency, high-stability optical parametric chirped-pulse amplification is demonstrated with a spatiotemporally shaped pump laser system. Broadband 5-mJ pulses are produced at a 5-Hz repetition rate with a pump-to-signal conversion efficiency of 29% and energy stability better than 2% rms. To our knowledge this is the highest conversion efficiency and stability achieved in an optical parametric chirped-pulse amplification system.
TL;DR: In this paper, the effects of contact resistance and side heat losses on the performance of high efficiency segmented thermoelectric unicouples (STUs) made of n-type Bi2Te3 and CoSb3-based alloys and p-type BTe3-CeFe4Sb12 based alloys have been analyzed.
TL;DR: Passive Q-switching performance was found to be greatly improved by use of a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4, and the resulting pulse energy, peak power, and pulse width were 181 microJ, 26 kW, and 6.8 ns, respectively.
Abstract: Passive Q-switching performance was found to be greatly improved by use of a new Nd-doped mixed vanadate crystal Nd:Gd0.64Y0.36VO4 compared with that achieved with Nd:YVO4 and Nd:GdVO4. At an absorbed pump power of 12 W, an average output power of 2.78 W was obtained at a pulse repetition frequency of 15.4 kHz with an optical conversion efficiency of 23.2%, and the slope efficiency was determined to be 45.5%. The resulting pulse energy, peak power, and pulse width were 181μJ, 26.6 kW, and 6.8 ns, respectively.
TL;DR: In this paper, an unamplified femtosecond Cr4+:forsterite laser in a submicron-thick film of a nanocrystalline ZnO pulsed-laser-deposited on a fused silica substrate was studied.
Abstract: Nonlinear optical conversion is studied in thin films of wide-bandgap materials. Very high conversion efficiency to the third-harmonic radiation is achieved for an unamplified femtosecond Cr4+:forsterite laser in a submicron-thick film of a nanocrystalline ZnO pulsed-laser-deposited on a fused silica substrate.
TL;DR: While single end pumping approaches the crystal fracture limit, double-end-pumping effectively divides the thermal loading between the two ends of the laser crystal, allowing for reduced risk of fracture and greater power-scalability.
Abstract: A Nd:YVO4 laser producing over 8W cw TEM00 at 1342nm with slope efficiency of 42% and optical to optical conversion efficiency of 33% has been demonstrated. Low neodymium doping concentration helps to reduce thermal loading in the laser crystal and increase achievable output power. While single end pumping approaches the crystal fracture limit, double-end-pumping effectively divides the thermal loading between the two ends of the laser crystal, allowing for reduced risk of fracture and greater power-scalability. Intracavity frequency doubling in LBO generated cw output powers over 900mW at 671nm.
TL;DR: In this article, an 85 mm long uncoated periodically polled MgO:LiNbO3 ridge-type waveguide by frequency doubling of a diode end-pumped Nd:Y3Al5O12 laser at room temperature was used for continuous-wave power of 189 mW at 473 nm with 49% conversion efficiency.
Abstract: Continuous-wave power of 189 mW at 473 nm with 49% conversion efficiency is generated from a 85 mm long uncoated periodically polled MgO:LiNbO3 ridge-type waveguide by frequency doubling of a diode end-pumped Nd:Y3Al5O12 laser at room temperature; the corresponding internal blue power and conversion efficiency were 222 mW and 58%, respectively The highest conversion efficiency of 63% (74% with respect to the blue internal power) was obtained from a 12 mm long waveguide with 99 mW blue output power Saturation of output blue power was observed for coupled fundamental power into the waveguides in excess of 200 mW
TL;DR: In this paper, the authors derived band gap restricted thermal enhanced solar water splitting efficiencies for both AM0 and AM1.5 insolation with contemporary thermodynamic values over a wide range of temperature and pressure conditions.
Abstract: A novel model is derived for electrochemical solar water splitting processes by semiconductors, which is the first derivation of band gap restricted thermal enhanced solar water splitting efficiencies. The theory combines photodriven charge transfer, with excess subband gap insolation to lower the water potential, providing a process of highly efficient elevated temperature solar electrolysis of water to H2 fuel. Solar water splitting can provide clean, renewable sources of H2 fuel. Prior models had indicated only low conversion efficiencies would be attainable. A theoretical basis is developed for solar energy conversion efficiencies in the 50% range as determined for both AM0 and AM1.5 insolation with contemporary thermodynamic values over a wide range of temperature and pressure conditions. The temperature and pressure consistent for a range of systems with various minimum band gaps, Eg min(T,p), are determined. At these values of T and p a photoelectonic conversion efficiency, ηphoto, yields a solar e...
TL;DR: In this article, a 1550-nm InAs-InP quantum-dash semiconductor optical amplifier with four-wave mixing (FWM) and cross-gain modulation (XGM) was used for short-pulse wavelength conversion over 10 THz and error-free data conversion of a 2.5Gb/s data sequence over 7.5 THz.
Abstract: Wavelength conversion based on four-wave mixing (FWM) and cross-gain modulation (XGM) is experimentally demonstrated for the first time in a 1550-nm InAs-InP quantum-dash semiconductor optical amplifier. Continuous-wave FWM with a symmetric conversion efficiency dependence on detuning direction and FWM mediated short-pulse wavelength conversion are demonstrated. Using XGM, we have successfully implemented short-pulse wavelength conversion over 10 THz and error-free data conversion of a 2.5-Gb/s data sequence over 7.5 THz. The pulsed XGM experiments suggest that adjacent regions within an inhomogeneously broadened gain spectrum are partially coupled which increases the operational bandwidth, but at the expense of speed.
TL;DR: In this article, the second harmonic generation in periodically poled KTiOPO4 (ppKTP) at 423 nm was achieved at a moderate input power of 400 mW.
25 Aug 2003
TL;DR: In this article, a power generator based on a vibration-to-electric energy converter using a variable-resonating capacitor is experimentally demonstrated, which consists of a complete system with a mechanical variable capacitor, a charge-transporting LC tank circuit and an externally powered timing-capture controller.
Abstract: A power generator based on a vibration-to-electric energy converter using a variable-resonating capacitor is experimentally demonstrated. The generator consists of a complete system with a mechanical variable capacitor, a charge-transporting LC tank circuit and an externally powered timing-capture controller. A practical design methodology to maximize the efficiency of the vibration-to-electric energy generation system is also described. The efficiency of the generator is estimated based on three factors: the mechanical-energy loss, the charge-transportation loss, and the timing-capture loss. Through the mechanical-energy analysis, the optimum condition for the resonance is found. The parasitic elements in the charge transporter and the timing management of the capture scheme dominate the generation efficiency. These analyses enable the optimum design of the energy-generation system. An experimentally fabricated and measured generator theoretically has a maximum power of 580 nW; the measured power is 120 nW, so conversion efficiency is 21%. This results from a 43% mechanical energy loss and a 63% charge-transportation loss. The timing-capture scheme is manually determined and externally powered in the experiment, so its efficiency is not considered. With our result, a new system LSI application with an embedded power source can be explored for the ubiquitous computing era.
TL;DR: An optical parametric chirped-pulse amplifier design that provides 40% pump-to-signal conversion efficiency and over-500-mJ signal energy at 1054 nm for front-end injection into a Nd:glass amplifier chain is presented.
Abstract: An optical parametric chirped-pulse amplifier (OPCPA) design that provides 40% pump-to-signal conversion efficiency and over-500-mJ signal energy at 1054 nm for front-end injection into a Nd:glass amplifier chain is presented. This OPCPA system is currently being built as the prototype front end for the OMEGA EP (extended performance) laser system at the University of Rochester’s Laboratory for Laser Energetics. Using a three-dimensional spatial and temporal numerical model, several design considerations necessary to achieve high conversion efficiency, good output stability, and good beam quality are discussed. The dependence of OPCPA output on the pump beam’s spatiotemporal shape and the relative size of seed and pump beams is described. This includes the effects of pump intensity modulation and pump-signal walk-off. The trade-off among efficiency, stability, and low output beam intensity modulation is discussed.
TL;DR: In this article, a poly(3-thiophenylacetic acid)-polymer-sensitized photoelectrochemical cells comprising of either mesoporous TiO2 or SnO2-ZnO electrodes and the electrolyte consisting with redox complex (I3−/I−) were fabricated and characterized.
Abstract: Poly(3-thiophenylacetic acid)-polymer-sensitized photoelectrochemical cells comprising of either mesoporous TiO2 or SnO2-ZnO electrodes and the electrolyte consisting with redox complex (I3−/I−) were fabricated and characterized. The addition of ionic liquid, 1-methyl- 3-n-hexylimidazolium iodide, into the electrolyte drastically enhanced the cell performance. The cells consisting of the nanoporous TiO2 electrodes showed the incident photon to current conversion efficiency as high as 60% (at 430 nm), while the highest overall power conversion efficiency was ∼2.4% under the irradiance of 100 mW cm−2 (air mass 1.5). The overall efficiency of the cells with nanoporous SnO2-ZnO electrodes was ∼1.5% under the same illumination.
TL;DR: In this paper, a conductive polymer, polyaniline, is used as a hole transport material to fabricate solid-state dye-sensitised TiO 2 solar cells.
TL;DR: In this paper, the authors presented results on p-i-n-type photovoltaic devices based on donor-acceptor organic small molecule blends and doped wide-gap charge transport layers.