scispace - formally typeset
Search or ask a question

Showing papers on "Energy conversion efficiency published in 2007"


Journal ArticleDOI
18 Oct 2007-Nature
TL;DR: These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis, and might find general usage as elements for powering ultralow-power electronics and diverse nanosystems.
Abstract: Solar cells are attractive candidates for clean and renewable power; with miniaturization, they might also serve as integrated power sources for nanoelectronic systems. The use of nanostructures or nanostructured materials represents a general approach to reduce both cost and size and to improve efficiency in photovoltaics. Nanoparticles, nanorods and nanowires have been used to improve charge collection efficiency in polymer-blend and dye-sensitized solar cells, to demonstrate carrier multiplication, and to enable low-temperature processing of photovoltaic devices. Moreover, recent theoretical studies have indicated that coaxial nanowire structures could improve carrier collection and overall efficiency with respect to single-crystal bulk semiconductors of the same materials. However, solar cells based on hybrid nanoarchitectures suffer from relatively low efficiencies and poor stabilities. In addition, previous studies have not yet addressed their use as photovoltaic power elements in nanoelectronics. Here we report the realization of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells. Under one solar equivalent (1-sun) illumination, the p-i-n silicon nanowire elements yield a maximum power output of up to 200 pW per nanowire device and an apparent energy conversion efficiency of up to 3.4 per cent, with stable and improved efficiencies achievable at high-flux illuminations. Furthermore, we show that individual and interconnected silicon nanowire photovoltaic elements can serve as robust power sources to drive functional nanoelectronic sensors and logic gates. These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis, and might find general usage as elements for powering ultralow-power electronics and diverse nanosystems.

2,879 citations


Journal ArticleDOI
TL;DR: In this paper, the authors review the processes and limitations that govern device operation of polymer-fullerene BHJ solar cells, with respect to the charge-carrier transport and photogeneration mechanism.
Abstract: Plastic solar cells bear the potential for large-scale power generation based on materials that provide the possibility of flexible, lightweight, inexpensive, efficient solar cells. Since the discovery of the photoinduced electron transfer from a conjugated polymer to fullerene molecules, followed by the introduction of the bulk heterojunction (BHJ) concept, this material combination has been extensively studied in organic solar cells, leading to several breakthroughs in efficiency, with a power conversion efficiency approaching 5 %. This article reviews the processes and limitations that govern device operation of polymer.-fullerene BHJ solar cells, with respect to the charge-carrier transport and photogeneration mechanism. The transport of electrons/holes in the blend is a crucial parameter and must be controlled (e.g., by controlling the nanoscale morphology) and enhanced in order to allow fabrication of thicker films to maximize the absorption, without significant recombination losses. Concomitantly, a balanced transport of electrons and holes in the blend is needed to suppress the build-up of the space-charge that will significantly reduce the power conversion efficiency. Dissociation of electron-hole pairs at the donor/acceptor interface is an important process that limits the charge generation efficiency under normal operation condition. Based on these findings, there is a compromise between charge generation (light absorption) and open-circuit voltage (V-oc) when attempting to reduce the bandgap of the polymer (or fullerene). Therefore, an increase in V-oc of polymer.-fullerene cells, for example by raising the lowest unoccupied molecular orbital level of the fullerene, will benefit cell performance as both fill factor and short-circuit current increase simultaneously.

1,987 citations


Journal ArticleDOI
TL;DR: An electron-transport polymer with good solution processibility, excellent thermal stability, and high electron affinity based on alternating perylene diimide and dithienothiophene units has been synthesized.
Abstract: An electron-transport polymer with good solution processibility, excellent thermal stability, and high electron affinity based on alternating perylene diimide and dithienothiophene units has been synthesized Electron mobilities as high as 13 × 10-2 cm2 V-1 s-1 have been measured in field-effect transistor geometry The polymer shows broad absorptions throughout the visible and extending into the near-IR A power conversion efficiency of over 1%, under simulated AM 15, 100 mW/cm2, was measured for a single-layer solar cell using this polymer as an acceptor and a polythiophene derivative as a donor

1,091 citations


Journal ArticleDOI
TL;DR: In this paper, a preparation technique of TiO2 screen-printing pastes from commercially available powders has been disclosed in order to fabricate the nanocrystalline layers without cracking and peeling off over 17'µm thickness for the photoactive electrodes of the dye-sensitised solar cells.
Abstract: A preparation technique of TiO2 screen-printing pastes from commercially-available powders has been disclosed in order to fabricate the nanocrystalline layers without cracking and peeling-off over 17 µm thickness for the photoactive electrodes of the dye-sensitised solar cells. A conversion efficiency of 8·7% was obtained by using a single-layer of a semi-transparent-TiO2 film. A conversion efficiency of 9·2% was obtained by using double-layers composed of transparent and light-scattering TiO2 films for a photon-trapping system. Copyright © 2007 John Wiley & Sons, Ltd.

999 citations


Journal ArticleDOI
TL;DR: In this paper, zinc oxide (ZnO) has been explored as an alternative material in dye-sensitized solar cells with great potential, and the main reasons for this increase in research surrounding ZnO material include: 1) zinc oxide having a band gap similar to that for TiO2 at 3.2 eV, and 2) Znoxide having a much higher electron mobility ~ 115-155 cm2/Vs.
Abstract: The interest in dye-sensitized solar cells has increased due to reduced energy sources and higher energy production costs. For the most part, titania (TiO2) has been the material of choice for dye-sensitized solar cells and so far have shown to exhibit the highest overall light conversion efficiency ~ 11%.[1] However, zinc oxide (ZnO) has recently been explored as an alternative material in dye-sensitized solar cells with great potential.[2] The main reasons for this increase in research surrounding ZnO material include: 1) ZnO having a band gap similar to that for TiO2 at 3.2 eV,[3] and 2) ZnO having a much higher electron mobility ~ 115-155 cm2/Vs[4] than that for anatase titania (TiO2), which is reported to be ~ 10-5 cm2/Vs.[5] In addition, ZnO has a few advantages as the semiconductor electrode when compared to TiO2, including 1) simpler tailoring of the nanostructure as compared to TiO2, and 2) easier modification of the surface structure. These advantages[6] are thought to provide a promising means for improving the solar cell performance of the working electrode in dye-sensitized solar cells.

516 citations


Journal ArticleDOI
TL;DR: Charge recombination is reduced by the presence of "ion-coordinating" moieties on the dye, with the longest electron lifetime and highest solar cell efficiency achieved using a novel sensitizer with diblock alkoxy-alkane pendent groups.
Abstract: We compare a series of molecular sensitizers in dye-sensitized solar cells containing the organic hole transporter 2,2‘,7,7‘-tetrakis(N,N-di-p-methoxypheny-amine)-9,9‘-spirobifluorene (spiro-MeOTAD). Charge recombination is reduced by the presence of “ion-coordinating” moieties on the dye, with the longest electron lifetime and highest solar cell efficiency achieved using a novel sensitizer with diblock alkoxy-alkane pendent groups. By further increasing the optical path length in the active layer, we achieve a power conversion efficiency of over 5% under simulated sun light.

369 citations


Journal ArticleDOI
TL;DR: RNAi technology was applied to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat and increase photosynthetic efficiencies under high-light conditions, resulting in an increased efficiency of cell cultivation under elevated light conditions.
Abstract: The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical 'fuels'. Increasingly, the photosynthetic machinery is being used for the production of biofuels such as bio-ethanol, biodiesel and bio-H-2. Fuel production efficiency is directly dependent on the solar photon capture and conversion efficiency of the system. Green algae (e.g. Chlamydomonas reinhardtii) have evolved genetic strategies to assemble large light-harvesting antenna complexes (LHC) to maximize light capture under low-light conditions, with the downside that under high solar irradiance, most of the absorbed photons are wasted as fluorescence and heat to protect against photodamage. This limits the production process efficiency of mass culture. We applied RNAi technology to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat. The mutant Stm3LR3 had significantly reduced levels of LHCI and LHCII mRNAs and proteins while chlorophyll and pigment synthesis was functional. The grana were markedly less tightly stacked, consistent with the role of LHCII. Stm3LR3 also exhibited reduced levels of fluorescence, a higher photosynthetic quantum yield and a reduced sensitivity to photoinhibition, resulting in an increased efficiency of cell cultivation under elevated light conditions. Collectively, these properties offer three advantages in terms of algal bioreactor efficiency under natural high-light levels: (i) reduced fluorescence and LHC-dependent heat losses and thus increased photosynthetic efficiencies under high-light conditions; (ii) improved light penetration properties; and (iii) potentially reduced risk of oxidative photodamage of PSII.

331 citations


Journal ArticleDOI
TL;DR: Polycrystalline n-ZnO/p-Cu2O heterojunctions have been fabricated by low-temperature eletrodepositions of ZnO and Cu2O layers in aqueous solutions as mentioned in this paper.
Abstract: Polycrystalline n-ZnO/p-Cu2O heterojunctions have been fabricated by low-temperature eletrodepositions of ZnO and Cu2O layers in aqueous solutions. The condition for forming the Cu2O layer significantly reflected the electrical rectification characteristic and the photovoltaic performance, and the heterojunction fabricated under optimized conditions showed an excellent electrical rectification characteristic and a photovoltaic performance of 1.28% in conversion efficiency under an AM 1.5 illumination.

317 citations


Journal ArticleDOI
TL;DR: The generation muJ-level, single-cycle terahertz pulses by optical rectification from a large-aperture ZnTe single crystal wafer is demonstrated using a 100 Hz Ti:sapphire laser source and a 75-mmdiameter, 0.5-mm-thick Zn Te crystal.
Abstract: We demonstrate the generation muJ-level, single-cycle terahertz pulses by optical rectification from a large-aperture ZnTe single crystal wafer. Energies up to 1.5 muJ per pulse and a spectral range extending to 3 THz were obtained using a 100 Hz Ti:sapphire laser source and a 75-mmdiameter, 0.5-mm-thick, (110) ZnTe crystal, corresponding to an average power of 150 muW and an energy conversion efficiency of 3.1 x 10(-5). We also demonstrate real-time imaging of the focused terahertz beam using a pyroelectric infrared camera.

303 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that tuning the parameters of an optical cavity induces filtering of different colours of light, which can also change the color of light. And they demonstrate a change in wavelength of up to 2.5 nm with up to 34% on-off conversion efficiency.
Abstract: As the demand for high bandwidths in microelectronic systems increases, optical interconnect architectures are now being considered that involve schemes commonly used in telecommunications, such as wavelength-division multiplexing (WDM) and wavelength conversion1. In such on-chip architectures, the ability to perform wavelength conversion is required. So far wavelength conversion on a silicon chip has only been demonstrated using schemes that are fundamentally all-optical2,3,4,5,6, making their integration on a microelectronic chip challenging. In contrast, we show wavelength conversion obtained by inducing ultrafast electro–optic tuning of a microcavity. It is well known that tuning the parameters of an optical cavity induces filtering of different colours of light7. Here we demonstrate that it can also change the colour of light. This is an effect often observed in other disciplines, for example, in acoustics, where the sound generated by a resonating guitar string can be modified by changing the length of the strings (that is, the resonators)8. Here we show this same tuning effect in optics, enabling compact on-chip electrical wavelength conversion. We demonstrate a change in wavelength of up to 2.5 nm with up to 34% on–off conversion efficiency.

283 citations


Journal ArticleDOI
TL;DR: In this paper, a spray deposition method was used for the fabrication of organic solar cells (OSCs), which showed 2.83% of power conversion efficiency and 52% of incident photon to current conversion efficiency even though the device was fabricated in air.
Abstract: The authors report on a spray deposition method as a cost-efficient technique for the fabrication of organic solar cells (OSCs). Active layers of OSCs were fabricated using conventional handheld airbrushes. Although the spray deposited film showed a relatively rougher surface than spin coated ones, pinhole-free and constant thickness films could be obtained. An optimized OSC showed 2.83% of power conversion efficiency and 52% of incident photon to current conversion efficiency even though the device was fabricated in air. The performance of sprayed OSCs was comparable to that of the spin coated devices fabricated in air.

Journal ArticleDOI
TL;DR: In this article, the significant effects of dye loading conditions on the overall light conversion efficiency of zinc oxide (ZnO) film electrodes in dye-sensitized solar cells were reported.
Abstract: In this paper, we report the significant effects of dye loading conditions on the overall light conversion efficiency of zinc oxide (ZnO) film electrodes in dye-sensitized solar cells. A comparison of the ZnO film electrodes was also made with TiO2 film electrodes prepared with similar dye loading conditions. It was found that using a higher and lower dye concentration requires a shorter and longer immersion time, respectively, for optimal sensitization of ZnO to obtain maximum efficiencies. A similar trend was found for the TiO2 film electrode as well; however, smaller differences in the overall light conversion efficiencies were observed with varying dye concentration and immersion time. It was found that the chemical stability was an issue for the ZnO film electrodes but was not pertinent for the TiO2 film electrodes. The film quality and structure of the ZnO film differed after prolonged immersion in high dye concentration, where the formation of N3 dye and Zn2+ aggregates and/or the deterioration of ...

Journal ArticleDOI
TL;DR: In this paper, the authors report efficient photovoltaic diodes which use poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7bis(3-hexylthien-5-yl]-2,1,3-benzothiadiazole]-2′,2″-diym) (F8TBT) both as electron acceptor, in blends with poly(3hexyl-thiophene), and as hole acceptor.
Abstract: The authors report efficient photovoltaic diodes which use poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) both as electron acceptor, in blends with poly(3-hexylthiophene), and as hole acceptor, in blends with (6,6)-phenyl C61-butyric acid methyl ester In both cases external quantum efficiencies of over 25% are achieved, with a power conversion efficiency of 18% under simulated sunlight for optimized F8TBT/poly(3-hexylthiophene) devices The ambipolar nature of F8TBT is also demonstrated by the operation of light-emitting F8TBT transistors The equivalent p- and n-type operation in this conjugated polymer represent an important extension of the range of useful n-type materials which may be developed

Journal ArticleDOI
TL;DR: In this paper, an integrated system combining highly efficient III-V solar cells in an optical concentrator system with a polymer electrolyte membrane electrolyser is presented, where hydrogen and oxygen are produced by solar water splitting.

Journal ArticleDOI
TL;DR: Dye-s Sensitized solar cells based on co-sensitization of organic dyes having complementary spectral absorption in the visible region resulted in a panchromatic response, which exhibited 86% incident monochromatic photon-to-current conversion efficiency in thevisible region.

Journal ArticleDOI
20 Sep 2007-Langmuir
TL;DR: The co-sensitized organic dye solar cell based on the newly developed binary ionic liquid (solvent-free) electrolyte gives 6.4% under AM 1.5 sunlight at 100 mW/cm2 irradiation, which is higher than that of individual dye-s Sensitized solar cells.
Abstract: The co-sensitization of two organic dyes (SQ1 and JK2), which are complementary in their spectral responses, shows enhanced photovoltaic performance compared with that of an individual organic dye-sensitized solar cell. The power conversion efficiency of the co-sensitized organic dye solar cell based on the newly developed binary ionic liquid (solvent-free) electrolyte gives 6.4% under AM 1.5 sunlight at 100 mW/cm2 irradiation, which is higher than that of individual dye-sensitized solar cells. The incident monochromatic photon-to-current conversion efficiency (IPCE) of the co-sensitized solar cell shows typical absorption peaks at 530 and 650 nm corresponding to the two dyes and displays a broad spectral response over the entire visible spectrum with IPCE of >40% in the 400−700 nm wavelength domain.

Journal ArticleDOI
TL;DR: In this article, a simple method is reported to systematically tune the band offset in a π-conjugated polymer-metal oxide hybrid donor-acceptor system in order to maximize the VOC.
Abstract: The power conversion efficiency of organic and hybrid solar cells is commonly reduced by a low open-circuit voltage (VOC). In these cases, the VOC is significantly less than the energy of the lowest energy absorbed photon, divided by the elementary charge q. The low photovoltage originates from characteristically large band offsets between the electron donor and acceptor species. Here a simple method is reported to systematically tune the band offset in a π-conjugated polymer–metal oxide hybrid donor–acceptor system in order to maximize the VOC. It is demonstrated that substitution of magnesium into a zinc oxide acceptor (ZnMgO) reduces the band offset and results in a substantial increase in the VOC of poly(3-hexylthiophene) (P3HT)–ZnMgO planar devices. The VOC is seen to increase from 500 mV at x = 0 up to values in excess of 900 mV for x = 0.35. A concomitant increase in overall device efficiency is seen as x is increased from 0 to 0.25, with a maximum power-conversion efficiency of 0.5 % obtained at x = 0.25, beyond which the efficiency decreases because of increased series resistance in the device. This work provides a new tool for understanding the role of the donor–acceptor band offset in hybrid photovoltaics and for maximizing the photovoltage and power-conversion efficiency in such devices.

Journal ArticleDOI
24 Oct 2007-Langmuir
TL;DR: Films comprised of 4 microm long titanium dioxide nanotube arrays were fabricated by anodizing Ti foils in an ethylene glycol based electrolyte to provide a stable rugged film and showed a maximum incident photon-to-electron conversion efficiency (IPCE) of 53% for the liquid junction cells and 25%" for the single heterojunction solid state solar cells.
Abstract: Films comprised of 4 microm long titanium dioxide nanotube arrays were fabricated by anodizing Ti foils in an ethylene glycol based electrolyte. A carboxylated polythiophene derivative was self-assembled onto the TiO2 nanotube arrays by immersing them in a solution of the polymer. The binding sites of the carboxylate moiety along the polymer chain provide multiple anchoring sites to the substrate, making for a stable rugged film. Backside illuminated liquid junction solar cells based on TiO2 nanotube films sensitized by the self-assembled polymeric layer showed a short-circuit current density of 5.5 mA cm-2, a 0.7 V open circuit potential, and a 0.55 fill factor yielding power conversion efficiencies of 2.1% under AM 1.5 sun. A backside illuminated single heterojunction solid state solar cell using the same self-assembled polymer was demonstrated and yielded a photocurrent density as high as 2.0 mA cm-2. When a double heterojunction was formed by infiltrating a blend of poly(3-hexylthiophene) (P3HT) and C60-methanofullerene into the self-assembled polymer coated nanotube arrays, a photocurrent as high as 6.5 mA cm-2 was obtained under AM 1.5 sun with a corresponding efficiency of 1%. The photocurrent action spectra showed a maximum incident photon-to-electron conversion efficiency (IPCE) of 53% for the liquid junction cells and 25% for the single heterojunction solid state solar cells.

Journal ArticleDOI
TL;DR: This device shows the highest light-to-electrical energy conversion efficiency based on plastic-substrate dye-sensitized solar cells, 7.4% under 100 mW cm(-2) (1 sun) AM1.5 illumination.

Journal ArticleDOI
TL;DR: Using a simple model, it is demonstrated that two- and three-photon absorption strongly limit the THz generation efficiency at high pump fluences in ZnTe and GaP.
Abstract: We demonstrate efficient generation of THz pulses by optical rectification of 1.03 um wavelength laser pulses in LiNbO3 using tilted pulse front excitation for velocity matching between the optical and THz fields. Pulse energies of 100 nJ with a spectral bandwidth of up to 2.5 THz were obtained at a pump energy of 400 uJ and 300 fs pulse duration. This conversion efficiency of 2.5×10-4 was an order of magnitude higher than that obtained with collinear optical recitification in GaP, and far higher still than that measured using ZnTe in an optimized geometry. Using a simple model we demonstrate that two- and three-photon absorption strongly limit the THz generation efficiency at high pump fluences in ZnTe and GaP respectively.

Journal ArticleDOI
TL;DR: In this paper, the influence of buffer layers on the performance of polymer photovoltaic devices based on blends of poly3-hexylthiophene and 6,6-phenyl-C-61-buytyric acid methyl ester has been investigated.
Abstract: The influence of anode buffer layers on the performance of polymer photovoltaic devices based on blends of poly3-hexylthiophene and 6,6-phenyl-C-61-buytyric acid methyl ester has been investigated. The buffer layers consist of poly3,4-ethylenedioxythiophene:polystyrenesulfonate PEDOT-PSS doped with different concentrations of mannitol. Improved power conversion efficiency, up to 5.2%, has been observed by reducing the resistance of PEDOT:PSS after doping. One extrapolation method has been developed to exclude the resistance from the connection of the electrodes from the total device resistance. The results confirm that the device improvement is due to the reduction of series resistance of the PEDOT:PSS after the mannitol doping. © 2007 American Institute of Physics. DOI: 10.1063/1.2437703 Organic photovoltaic devices PVs have attracted considerable attention due to their potential for flexible, lightweight, and low-cost applications of solar energy conversion. Recently, the power conversion efficiency PCE of photovoltaic cells around 5% has been realized. 1,2 In addition, through the optimization of the donor/acceptor energy levels, the efficiency up to 10% is expected from recent simulation

Journal ArticleDOI
TL;DR: In this article, organic solar cells based on pentacene/C60 heterojunctions were encapsulated using a 200nm-thick film of Al2O3 deposited by atomic layer deposition (ALD).
Abstract: Organic solar cells based on pentacene/C60 heterojunctions were encapsulated using a 200-nm-thick film of Al2O3 deposited by atomic layer deposition (ALD). Encapsulated devices maintained power conversion efficiency after exposure to ambient atmosphere for over 6000h, while devices with no encapsulation degraded rapidly after only 10h of air exposure. In addition, thermal annealing associated with the ALD deposition is shown to improve the open-circuit voltage and power conversion efficiency of the solar cells.

Journal ArticleDOI
TL;DR: The current cost distribution of a crystalline silicon PV module is clearly dominated by material costs, especially by the costs of the silicon wafer, therefore cell designs that allow the use of thinner wafers and the increase of energy conversion efficiency are of special interest to the PV industry as discussed by the authors.
Abstract: The current cost distribution of a crystalline silicon PV module is clearly dominated by material costs, especially by the costs of the silicon wafer. Therefore cell designs that allow the use of thinner wafers and the increase of energy conversion efficiency are of special interest to the PV industry. This article gives an overview of the most critical issues to achieve this aim and of the recent activities at Fraunhofer ISE and other institutes.

Journal ArticleDOI
TL;DR: In this paper, a reflective tandem photovoltaic cell where single cells are reflecting the nonabsorbed light upon another adjacent cell is demonstrated, and spectral broadening and light trapping are combined to give an enhancement of power conversion efficiency of a factor of 1.8±0.3.
Abstract: Conjugated polymers are promising materials for the production of inexpensive and flexible photovoltaic cells. Organic materials display tunable optical absorption within a large spectral range. This enables the construction of organic tandem photovoltaic cells. The authors here demonstrate a reflective tandem cell where single cells are reflecting the nonabsorbed light upon another adjacent cell. By folding two planar but spectrally different cells toward each other, spectral broadening and light trapping are combined to give an enhancement of power conversion efficiency of a factor of 1.8±0.3.

Journal ArticleDOI
TL;DR: In this paper, the photovoltaic properties of organic solar cells based on pentacene and C 60 thin films with a focus on their spectral responses and the effect of thermal annealing were analyzed.
Abstract: We report on the photovoltaic properties of organic solar cells based on pentacene and C 60 thin films with a focus on their spectral responses and the effect of thermal annealing. Spectra of external quantum efficiency (EQE) are measured and analyzed with a one-dimensional exciton diffusion model dependent upon the complex optical functions of pentacene films, which are measured by spectroscopic ellipsometry. An improvement in EQE is observed when the thickness of the bathocuproine (BCP) layer is decreased from 12 nm to 6 nm. Detailed analysis of the EQE spectra indicates that large exciton diffusion lengths in the pentacene films are responsible for the overall high EQE values near wavelengths of 668 nm. Analysis also shows that improvement in the EQE of devices with the thinner BCP layer can be attributed to a net gain in optical field distribution and improvement in carrier collection efficiency. An improvement in open-circuit voltage ( V OC ) is also achieved through a thermal annealing process, leading to a net increase in power conversion efficiency. Integration of the EQE spectrum with an AM1.5 G spectrum yields a predicted power conversion efficiency of 1.8 ± 0.2%. The increase in V OC is attributed to a significant reduction in the diode reverse saturation current upon annealing.

Journal ArticleDOI
TL;DR: In this article, the authors derived general conditions for 100 percent frequency conversion in any doubly resonant nonlinear cavity, for both second and third-harmonic generation via chi2 and chi3 nonlinearities.
Abstract: We derive general conditions for 100 percent frequency conversion in any doubly resonant nonlinear cavity, for both second- and third-harmonic generation via chi2 and chi3 nonlinearities. We find that conversion efficiency is optimized for a certain critical power depending on the cavity parameters, and assuming reasonable parameters we predict 100 percent conversion using milliwatts of power or less. These results follow from a semi-analytical coupled-mode theory framework which is generalized from previous work to include both chi2 and chi3 media as well as inhomogeneous (fully vectorial) cavities, analyzed in the high-efficiency limit where down-conversion processes lead to a maximum efficiency at the critical power, and which is verified by direct finite-difference time-domain (FDTD) simulations of the nonlinear Maxwell equations. Explicit formulas for the nonlinear coupling coefficients are derived in terms of the linear cavity eigenmodes, which can be used to design and evaluate cavities in arbitrary geometries.

Journal ArticleDOI
TL;DR: In this article, a new implantation-free lift-off process is presented, where a layer with mismatched thermal expansion coefficient with respect to the substrate is deposited, and upon cooling, the differential contraction induces a large stress field which is released by the initiation and the propagation of a crack parallel to the surface.
Abstract: A new implantation-free lift-off process is presented. We deposit a layer with mismatched thermal expansion coefficient with respect to the substrate. Upon cooling, the differential contraction induces a large stress field which is released by the initiation and the propagation of a crack parallel to the surface. The principle is demonstrated on both single and multi-crystalline silicon. Films with an area of 25 cm2 and a thickness of 30–50 μm have been obtained. Some Si layers were further processed into solar cells. An energy conversion efficiency of 9.9% was reached on a 1 cm2 sample.

Journal ArticleDOI
TL;DR: To eliminate charge trapping, a p+-i-n+ cell employing QDs buried within a high band gap barrier layer is proposed and analyzed and represents a significant improvement over GaAs homojunction cells with maximum efficiencies of <25%.
Abstract: Power efficiencies >60% have been predicted for idealized quantum dot (QD) intermediate band solar cells. This goal has not yet been realized, due in part to nonidealities that result in charge trapping followed by recombination of photocarriers in the QDs, and the lack of an optimal materials combination. To eliminate charge trapping, a p+−i−n+ cell employing QDs buried within a high band gap barrier layer is proposed and analyzed. The maximum solar power conversion efficiency under AM1.5 spectral radiation of an example GaAs-based photovoltaic cell employing 10−20 layers of InAs QDs surrounded by AlxGa1-xAs barriers in the junction built-in depletion region can be as high as 45%. Higher efficiencies are anticipated for InP-based cells. This represents a significant improvement over GaAs homojunction cells with maximum efficiencies of <25%.

Journal ArticleDOI
TL;DR: The Mercury laser project as discussed by the authors developed key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications.
Abstract: Hundred-joule, kilowatt-class lasers based on diode-pumped solid-state technologies, are being developed worldwide for laser-plasma interactions and as prototypes for fusion energy drivers. The goal of the Mercury Laser Project is to develop key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications. Mercury has requirements that include: scalability to IFE beamlines, 10 Hz repetition rate, high efficiency, and 10 9 shot reliability. The Mercury laser has operated continuously for several hours at 55 J and 10 Hz with fourteen 4 x 6 cm 2 ytterbium doped strontium fluoroapatite amplifier slabs pumped by eight 100 kW diode arrays. A portion of the output 1047 nm was converted to 523 nm at 160 W average power with 73% conversion efficiency using yttrium calcium oxy-borate (YCOB).

Journal ArticleDOI
TL;DR: The potential of using photonic crystal structures for realizing highly efficient and reliable solar-cell devices is presented in this paper, where photonic crystals emerge as one of the leading candidates for frequency and angular-selective radiating elements in thermophotovoltaic devices.