Showing papers on "Absorption (electromagnetic radiation) published in 2011"
TL;DR: It is demonstrated that MEG charge carriers can be collected in suitably designed QD solar cells, providing ample incentive to better understand MEG within isolated and coupled QDs as a research path to enhancing the efficiency of solar light harvesting technologies.
Abstract: Multiple exciton generation (MEG) is a process that can occur in semiconductor nanocrystals, or quantum dots (QDs), whereby absorption of a photon bearing at least twice the bandgap energy produces two or more electron-hole pairs. Here, we report on photocurrent enhancement arising from MEG in lead selenide (PbSe) QD-based solar cells, as manifested by an external quantum efficiency (the spectrally resolved ratio of collected charge carriers to incident photons) that peaked at 114 ± 1% in the best device measured. The associated internal quantum efficiency (corrected for reflection and absorption losses) was 130%. We compare our results with transient absorption measurements of MEG in isolated PbSe QDs and find reasonable agreement. Our findings demonstrate that MEG charge carriers can be collected in suitably designed QD solar cells, providing ample incentive to better understand MEG within isolated and coupled QDs as a research path to enhancing the efficiency of solar light harvesting technologies.
1,537 citations
TL;DR: An ultrathin (260 nm) plasmonic super absorber consisting of a metal-insulator-metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays yields broadband and polarization-independent resonant light absorption over the entire visible spectrum.
Abstract: Resonant plasmonic and metamaterial structures allow for control of fundamental optical processes such as absorption, emission and refraction at the nanoscale. Considerable recent research has focused on energy absorption processes, and plasmonic nanostructures have been shown to enhance the performance of photovoltaic and thermophotovoltaic cells. Although reducing metallic losses is a widely sought goal in nanophotonics, the design of nanostructured 'black' super absorbers from materials comprising only lossless dielectric materials and highly reflective noble metals represents a new research direction. Here we demonstrate an ultrathin (260 nm) plasmonic super absorber consisting of a metal–insulator–metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays. Our super absorber yields broadband and polarization-independent resonant light absorption over the entire visible spectrum (400–700 nm) with an average measured absorption of 0.71 and simulated absorption of 0.85. Proposed nanostructured absorbers open a path to realize ultrathin black metamaterials based on resonant absorption.
1,532 citations
TL;DR: In this paper, a heterojunction electrode was fabricated by layer-by-layer deposition of WO3 and BiVO4 on a conducting glass, and investigated for photoelectrochemical water oxidation under simulated solar light.
Abstract: Heterojunction electrodes were fabricated by layer-by-layer deposition of WO3 and BiVO4 on a conducting glass, and investigated for photoelectrochemical water oxidation under simulated solar light. The electrode with the optimal composition of four layers of WO3 covered by a single layer of BiVO4 showed enhanced photoactivity by 74% relative to bare WO3 and 730% relative to bare BiVO4. According to the flat band potential and optical band gap measurements, both semiconductors can absorb visible light and have band edge positions that allow the transfer of photoelectrons from BiVO4 to WO3. The electrochemical impedance spectroscopy revealed poor charge transfer characteristics of BiVO4, which accounts for the low photoactivity of bare BiVO4. The measurements of the incident photon-to-current conversion efficiency spectra showed that the heterojunction electrode utilized effectively light up to 540 nm covering absorption by both WO3 and BiVO4 layers. Thus, in heterojunction electrodes, the photogenerated electrons in BiVO4 are transferred to WO3 layers with good charge transport characteristics and contribute to the high photoactivity. They combine merits of the two semiconductors, i.e. excellent charge transport characteristics of WO3 and good light absorption capability of BiVO4 for enhanced photoactivity.
1,023 citations
TL;DR: In this article, the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and Fe 2O3 by reduction−oxidation process.
Abstract: Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2−18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction−oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3.
866 citations
Abstract: A microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated. It is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids. These pyramids possess resonant absorption modes at multi-frequencies, of which the overlapping leads to the total absorption of the incident wave over an ultra-wide spectral band. The experimental absorption at normal incidence is above 90% in the frequency range of 7.8-14.7GHz, and the absorption is kept large when the incident angle is smaller than 60 degrees. The experimental results agree well with the numerical simulation.
764 citations
TL;DR: The device, termed a “coherent perfect absorber,” functions as an absorptive interferometer, with potential practical applications in integrated optics, and it is demonstrated that absorption can be reduced substantially by varying the relative phase of the incident fields.
Abstract: In the time-reversed counterpart to laser emission, incident coherent optical fields are perfectly absorbed within a resonator that contains a loss medium instead of a gain medium. The incident fields and frequency must coincide with those of the corresponding laser with gain. We demonstrated this effect for two counterpropagating incident fields in a silicon cavity, showing that absorption can be enhanced by two orders of magnitude, the maximum predicted by theory for our experimental setup. In addition, we showed that absorption can be reduced substantially by varying the relative phase of the incident fields. The device, termed a “coherent perfect absorber,” functions as an absorptive interferometer, with potential practical applications in integrated optics.
745 citations
TL;DR: In this paper, an ultra broadband thin-film infrared absorber made of saw-toothed anisotropic metamaterial is presented, where light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths.
Abstract: We present an ultra broadband thin-film infrared absorber made of saw-toothed anisotropic metamaterial. Absorbtivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.
736 citations
TL;DR: In this paper, a systematic study of the mechanisms of Au nanoparticle/TiO2-catalyzed photoreduction of CO2 and water vapor is carried out over a wide range of wavelengths.
Abstract: A systematic study of the mechanisms of Au nanoparticle/TiO2-catalyzed photoreduction of CO2 and water vapor is carried out over a wide range of wavelengths. When the photon energy matches the plasmon resonance of the Au nanoparticles (free carrier absorption), which is in the visible range (532 nm), we observe a 24-fold enhancement in the photocatalytic activity because of the intense local electromagnetic fields created by the surface plasmons of the Au nanoparticles. These intense electromagnetic fields enhance sub-bandgap absorption in the TiO2, thereby enhancing the photocatalytic activity in the visible range. When the photon energy is high enough to excite d band electronic transitions in the Au, in the UV range (254 nm), a different mechanism occurs resulting in the production of additional reaction products, including C2H6, CH3OH, and HCHO. This occurs because the energy of the d band excited electrons lies above the redox potentials of the additional reaction products CO2/C2H6, CO2/CH3OH, and CO...
487 citations
TL;DR: Comparisons with measured extinction coefficients reveal that the approximation works well with water-based nanofluids containing graphite nanoparticles but less well with metallic nanoparticles and/or oil-based fluids.
Abstract: Suspensions of nanoparticles (i.e., particles with diameters < 100 nm) in liquids, termed nanofluids, show remarkable thermal and optical property changes from the base liquid at low particle loadings. Recent studies also indicate that selected nanofluids may improve the efficiency of direct absorption solar thermal collectors. To determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known. That is, their absorption of the solar spectrum must be established. Accordingly, this study compares model predictions to spectroscopic measurements of extinction coefficients over wavelengths that are important for solar energy (0.25 to 2.5 μm). A simple addition of the base fluid and nanoparticle extinction coefficients is applied as an approximation of the effective nanofluid extinction coefficient. Comparisons with measured extinction coefficients reveal that the approximation works well with water-based nanofluids containing graphite nanoparticles but less well with metallic nanoparticles and/or oil-based fluids. For the materials used in this study, over 95% of incoming sunlight can be absorbed (in a nanofluid thickness ≥10 cm) with extremely low nanoparticle volume fractions - less than 1 × 10-5, or 10 parts per million. Thus, nanofluids could be used to absorb sunlight with a negligible amount of viscosity and/or density (read: pumping power) increase.
477 citations
TL;DR: In this article, the authors theoretically and numerically study the absorption effect and the heat generation in plasmonic metamaterials under light radiation at their plasmoric resonance.
Abstract: We theoretically and numerically study the absorption effect and the heat generation in plasmonic metamaterials under light radiation at their plasmonic resonance. Three different types of structures, all possessing high-performance absorption for visible lights, are investigated. The main aim of this work is to present an intuitive and original understanding of the high-performance absorption effects. From the macroscopic electromagnetic point of view, the effective-medium approach is used to describe the absorption effects of the plasmonic metamaterials. On the other hand, the field distributions and heat generation effects in such plasmonic nanostructures are investigated, which also provides a satisfactory qualitative description of such absorption behavior based upon the microscopic perspective.
464 citations
TL;DR: It is demonstrated that plasmonic resonances in metallic nanostructures and multilayer interference effects can be engineered to strongly concentrate sunlight close to the electrode/liquid interface, precisely where the relevant reactions take place.
Abstract: Future generations of photoelectrodes for solar fuel generation must employ inexpensive, earth-abundant absorber materials in order to provide a large-scale source of clean energy. These materials tend to have poor electrical transport properties and exhibit carrier diffusion lengths which are significantly shorter than the absorption depth of light. As a result, many photo-excited carriers are generated too far from a reactive surface, and recombine instead of participating in solar-to-fuel-conversion. We demonstrate that plasmonic resonances in metallic nanostructures and multi-layer interference effects can be engineered to strongly concentrate sunlight close to the electrode/liquid interface, precisely where the relevant reactions take place. By comparing spectral features in the enhanced photocurrent spectra to full-field electromagnetic simulations, the contribution of surface plasmon excitations is verified. These results open the door to the optimization of a wide variety of photochemical processes by leveraging the rapid advances in the field of plasmonics.
TL;DR: In this article, the authors show that dispersed functionalized graphene can exhibit broadband nonlinear optical absorption at fluences well below the damage threshold and obtain an optical energy-limiting onset benchmark of 10 mJ cm−2 at a linear transmittance of 70% for nanosecond visible and near-infrared pulses.
Abstract: Researchers show that dispersed functionalized graphene can exhibit broadband nonlinear optical absorption at fluences well below the damage threshold. An optical energy-limiting onset benchmark of 10 mJ cm−2 at a linear transmittance of 70% was obtained for nanosecond visible and near-infrared pulses. The findings shed light on the formation of practical thin films with broadband optical limiting characteristics.
TL;DR: In this paper, plasmonic resonances in metallic nanostructures and multilayer interference effects can be engineered to strongly concentrate sunlight close to the electrode/liquid interface, precisely where the relevant reactions take place.
Abstract: Future generations of photoelectrodes for solar fuel generation must employ inexpensive, earth-abundant absorber materials in order to provide a large-scale source of clean energy. These materials tend to have poor electrical transport properties and exhibit carrier diffusion lengths which are significantly shorter than the absorption depth of light. As a result, many photoexcited carriers are generated too far from a reactive surface and recombine instead of participating in solar-to-fuel conversion. We demonstrate that plasmonic resonances in metallic nanostructures and multilayer interference effects can be engineered to strongly concentrate sunlight close to the electrode/liquid interface, precisely where the relevant reactions take place. On comparison of spectral features in the enhanced photocurrent spectra to full-field electromagnetic simulations, the contribution of surface plasmon excitations is verified. These results open the door to the optimization of a wide variety of photochemical process...
TL;DR: In this article, the intrinsic properties of monolayer graphene allow it to act as a more effective saturable absorber for mode-locking fiber lasers when compared to multilayer graphene.
Abstract: We demonstrate that the intrinsic properties of monolayer graphene allow it to act as a more effective saturable absorber for mode-locking fiber lasers when compared to multilayer graphene. The absorption of monolayer graphene can be saturated at lower excitation intensity compared to multilayer graphene, graphene with wrinkle-like defects, or functionalized graphene. Monolayer graphene has a remarkably large modulation depth of 65.9%, whereas the modulation depth of multilayer graphene is greatly reduced due to nonsaturable absorption and scattering loss. Picosecond ultrafast laser pulses (1.23 ps) can be generated using monolayer graphene as a saturable absorber. Due to the ultrafast relaxation time, larger modulation depth and lower scattering loss of monolayer graphene, it performs better than multilayer graphene in terms of pulse shaping ability, pulse stability, and output energy.
TL;DR: It is shown that treatment of graphene with xenon difluoride produces a partially fluorinated graphene (fluorographene) with covalent C-F bonding and local sp(3)-carbon hybridization, suggesting the use of fluorographane as a new, readily prepared material for electronic, optoelectronic applications, and energy harvesting applications.
Abstract: The manipulation of the bandgap of graphene by various means has stirred great interest for potential applications. Here we show that treatment of graphene with xenon difluoride produces a partially fluorinated graphene (fluorographene) with covalent C−F bonding and local sp3-carbon hybridization. The material was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, electron energy loss spectroscopy, photoluminescence spectroscopy, and near edge X-ray absorption spectroscopy. These results confirm the structural features of the fluorographane with a bandgap of 3.8 eV, close to that calculated for fluorinated single layer graphene, (CF)n. The material luminesces broadly in the UV and visible light regions, and has optical properties resembling diamond, with both excitonic and direct optical absorption and emission features. These results suggest the use of fluorographane as a new, readily prepared material for electronic, optoelectronic applications, and energy harvesting applications.
TL;DR: An ultrathin solar cell architecture that combines the benefits of both plasmonic photovoltaics and traditional antireflection coatings is described, and the improved absorption is mainly attributed to improved coupling to guided modes rather than localized resonant modes.
Abstract: We describe an ultrathin solar cell architecture that combines the benefits of both plasmonic photovoltaics and traditional antireflection coatings. Spatially resolved electron generation rates are used to determine the total integrated current improvement under AM1.5G solar illumination, which can reach a factor of 1.8. The frequency-dependent absorption is found to strongly correlate with the occupation of optical modes within the structure, and the improved absorption is mainly attributed to improved coupling to guided modes rather than localized resonant modes.
TL;DR: Investigation optical power is transferred to the thin-film cell by leaky mode coupling into a thin solar cell absorber layer and significantly enhances its efficiency by increasing the fraction of incident light absorbed.
Abstract: Freely propagating sunlight can be diffractively coupled and transformed into several guided whispering gallery modes within an array of wavelength scale dielectric spheres. Incident optical power is then transferred to the thin-film cell by leaky mode coupling into a thin solar cell absorber layer and significantly enhances its efficiency by increasing the fraction of incident light absorbed.
TL;DR: This paper demonstrates a conformal metamaterial absorber with a narrow band, polarization-independent absorptivity of >90% over a wide ±50° angular range centered at mid-infrared wavelengths of 3.3 and 3.9 μm, making it attractive for advanced coatings that suppress the infrared reflection from the protected surface.
Abstract: Metamaterials offer a new approach to create surface coatings with highly customizable electromagnetic absorption from the microwave to the optical regimes. Thus far, efficient metamaterial absorbers have been demonstrated at microwave frequencies, with recent efforts aimed at much shorter terahertz and infrared wavelengths. The present infrared absorbers have been constructed from arrays of nanoscale metal resonators with simple circular or cross-shaped geometries, which provide a single band response. In this paper, we demonstrate a conformal metamaterial absorber with a narrow band, polarization-independent absorptivity of >90% over a wide ±50° angular range centered at mid-infrared wavelengths of 3.3 and 3.9 μm. The highly efficient dual-band metamaterial was realized by using a genetic algorithm to identify an array of H-shaped nanoresonators with an effective electric and magnetic response that maximizes absorption in each wavelength band when patterned on a flexible Kapton and Au thin film substrat...
TL;DR: In this paper, a simple metamaterial-based wide-angle plasmonic absorber is introduced, fabricated, and experimentally characterized using angle-resolved infrared spectroscopy.
Abstract: A simple metamaterial-based wide-angle plasmonic absorber is introduced, fabricated, and experimentally characterized using angle-resolved infrared spectroscopy. The metamaterials are prepared by nano-imprint lithography, an attractive low-cost technology for making large-area samples. The matching of the metamaterial's impedance to that of vacuum is responsible for the observed spectrally selective ``perfect'' absorption of infrared light. The impedance is theoretically calculated in the single-resonance approximation, and the responsible resonance is identified as a short-range surface plasmon. The spectral position of the absorption peak (which is as high as $95%$) is experimentally shown to be controlled by the metamaterial's dimensions. The persistence of ``perfect'' absorption with variable metamaterial parameters is theoretically explained. The wide-angle nature of the absorber can be utilized for subdiffraction-scale infrared pixels exhibiting spectrally selective absorption/emissivity.
TL;DR: A new architecture based on surface plasmon excitation within a metal-insulator-metal device that produces power based on spatial confinement of electron excitation through plAsmon absorption is shown.
Abstract: Conversion of light into direct current is important for applications ranging from energy conversion to photodetection, yet often challenging over broad photon frequencies. Here we show a new architecture based on surface plasmon excitation within a metal–insulator–metal device that produces power based on spatial confinement of electron excitation through plasmon absorption. Plasmons excited in the upper metal are absorbed, creating a high concentration of hot electrons which can inject above or tunnel through the thin insulating barrier, producing current. The theoretical power conversion efficiency enhancement achieved can be almost 40 times larger than that of direct illumination while utilizing a broad spectrum of IR to visible wavelengths. Here we present both theoretical estimates of the power conversion efficiency and experimental device measurements, which show clear rectification and power conversion behavior.
TL;DR: The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical-phonon frequency; however, owing to the presence of hot carriers, optical-Phonon emission is still the predominant relaxation process.
Abstract: We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 to 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical-phonon frequency; however, owing to the presence of hot carriers, optical-phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes.
TL;DR: It is shown that hot electron flow generated on a gold thin film by photon absorption (or internal photoemission) is amplified by localized surface plasmon resonance.
Abstract: A continuous flow of hot electrons that are not at thermal equilibrium with the surrounding metal atoms is generated by the absorption of photons. Here we show that hot electron flow generated on a gold thin film by photon absorption (or internal photoemission) is amplified by localized surface plasmon resonance. This was achieved by direct measurement of photocurrent on a chemically modified gold thin film of metal-semiconductor (TiO2) Schottky diodes. The short-circuit photocurrent obtained with low-energy photons is consistent with Fowler’s law, confirming the presence of hot electron flows. The morphology of the metal thin film was modified to a connected gold island structure after heating such that it exhibits surface plasmon. Photocurrent and optical measurements on the connected island structures revealed the presence of a localized surface plasmon at 550 ± 20 nm. The results indicate an intrinsic correlation between the hot electron flow generated by internal photoemission and localized surface p...
TL;DR: In this article, the concept of wavelength-dependent absorption Angstrom coefficients (AACs) is discussed and clarified for both single and two-wavelengths AACs and guidance for their implementation with noisy absorption spectra is provided.
Abstract: . The concept of wavelength-dependent absorption Angstrom coefficients (AACs) is discussed and clarified for both single and two-wavelengths AACs and guidance for their implementation with noisy absorption spectra is provided. This discussion is followed by application of the concept to models for brown carbon bulk absorption spectra including the damped simple harmonic oscillator model, its Lorentzian approximation, and the band-gap model with and without Urbach tail. We show that the band-gap model with Urbach tail always has an unphysical discontinuity in the first derivative of the AAC at the band-gap – Urbach-tail matching wavelength. Complex refractive indices obtained from the bulk damped simple harmonic oscillator model are used to calculate absorption spectra for spherical particles, followed by a discussion of their features. For bulk material and small particles, this model predicts a monotonic decrease of the AAC with wavelength well above the resonance wavelength; the model predicts a monotonic increase for large particles.
TL;DR: This first measurement of ultrasound absorption in bone can be used to estimate the amount of heat deposition based on knowledge of the acoustic field and it is demonstrated that only a small part of the attenuation is due to absorption inBone and that the majority of the dBs are due to reflection, scattering, and mode conversion.
Abstract: (Received 27 June 2011; revised 26 October 2011; accepted for publication 22 November 2011;published 21 December 2011)Purpose: Measured values of ultrasound attenuation in bone represent a combination of differentloss mechanisms. As a wave is transmitted from a fluid into bone, reflections occur at the interface.In the bone, mode conversion occurs between longitudinal and shear modes and the mechanicalwave is scattered by its complex internal microstructure. Finally, part of the wave energy isabsorbed by the bone and converted into heat. Due to the complexity of the wave propagation andthe difficulty in performing measurements that are capable of separating the various loss mecha-nisms, there are currently no estimates of the absorption in bone. The aim of this paper is, thus, toquantify the attenuation, scattering, and thermal absorption in bone.Methods: An attenuating model of wave propagation in bone is established and used to develop athree-dimensional finite difference time domain numerical algorithm. Hydrophone and optical het-erodyne interferometer measurements of the acoustic field as well as a x-ray microtomography ofthe bone sample are used to drive the simulations and to measure the attenuation. The acousticmeasurements are performed concurrently with an infrared camera that can measure the tempera-ture elevation during insonication. A link between the temperature and the absorption via a three-dimensional thermal simulation is then used to quantify the absorption coefficients for longitudinaland shear waves in cortical bone.Results: We demonstrate that only a small part of the attenuation is due to absorption in bone andthat the majority of the attenuation is due to reflection, scattering, and mode conversion. In the ninesamples of a human used for the study, the absorption time constant for cortical bone was deter-mined to be 1.04 ls628%. This corresponds to a longitudinal absorption of 2.7 dB/cm and a shearabsorption of 5.4 dB/cm. The experimentally measured attenuation across the approximately 8 mmthick samples was 13.360.97 dB/cm.Conclusions: This first measurement of ultrasound absorption in bone can be used to estimate theamount of heat deposition based on knowledge of the acoustic field.
TL;DR: 3D-photonic crystal design was utilized to enhance incident photon-to-electron conversion efficiency (IPCE) of WO(3) photoanodes with inverse opal structure and can provide a potential and promising approach to effectively utilize solar energy in visible-light-responsive photoanode.
Abstract: In this study, 3D-photonic crystal design was utilized to enhance incident photon-to-electron conversion efficiency (IPCE) of WO3 photoanodes. Large-area and high-quality WO3 photonic crystal photoanodes with inverse opal structure were prepared. The photonic stop-bands of these WO3 photoanodes were tuned experimentally by variation of the pore size of inverse opal structures. It was found that when the red-edge of the photonic stop-band of WO3 inverse opals overlapped with the WO3 electronic absorption edge at Eg = 2.6–2.8 eV, a maximum of 100% increase in photocurrent intensity was observed under visible light irradiation (λ > 400 nm) in comparison with a disordered porous WO3 photoanode. When the red-edge of the stop-band was tuned well within the electronic absorption range of WO3, noticeable but less amplitude of enhancement in the photocurrent intensity was observed. It was further shown that the spectral region with a selective IPCE enhancement of the WO3 inverse opals exhibited a blue-shift in wav...
Leibniz Association1, Netherlands Organisation for Applied Scientific Research2, Finnish Meteorological Institute3, University of Helsinki4, Bulgarian Academy of Sciences5, University of Ljubljana6, MeteoSwiss7, Stockholm University8, University of Pannonia9, National University of Ireland, Galway10, China Meteorological Administration11, University of Crete12, Blaise Pascal University13, Joseph Fourier University14, Environment Canada15, Norwegian Institute for Air Research16, Earth System Research Laboratory17, University of Huelva18, Spanish National Research Council19, Paul Scherrer Institute20
TL;DR: In this paper, the authors compared the performance of different types of absorption photometers for real-time analysis of aerosol particles. But, the results showed that the current corrections of a cross sensitivity to particle scattering are not sufficient and the remaining cross sensitivities were a function of the total particle load on the filter.
Abstract: . Absorption photometers for real time application have been available since the 1980s, but the use of filter-based instruments to derive information on aerosol properties (absorption coefficient and black carbon, BC) is still a matter of debate. Several workshops have been conducted to investigate the performance of individual instruments over the intervening years. Two workshops with large sets of aerosol absorption photometers were conducted in 2005 and 2007. The data from these instruments were corrected using existing methods before further analysis. The inter-comparison shows a large variation between the responses to absorbing aerosol particles for different types of instruments. The unit to unit variability between instruments can be up to 30% for Particle Soot Absorption Photometers (PSAPs) and Aethalometers. Multi Angle Absorption Photometers (MAAPs) showed a variability of less than 5%. Reasons for the high variability were identified to be variations in sample flow and spot size. It was observed that different flow rates influence system performance with respect to response to absorption and instrumental noise. Measurements with non absorbing particles showed that the current corrections of a cross sensitivity to particle scattering are not sufficient. Remaining cross sensitivities were found to be a function of the total particle load on the filter. The large variation between the response to absorbing aerosol particles for different types of instruments indicates that current correction functions for absorption photometers are not adequate.
TL;DR: In this article, the authors investigated the absorption spectrum and the alignment of ground and excited state energies for the prototypical N719 Ru(II) sensitizer adsorbed on an extended TiO2 model by means of high level DFT/TDDFT calculations.
Abstract: We have investigated the absorption spectrum and the alignment of ground and excited state energies for the prototypical N719 Ru(II) sensitizer adsorbed on an extended TiO2 model by means of high level DFT/TDDFT calculations. The calculated and experimental absorption spectra for the dye on TiO2 are in excellent agreement over the explored energy range, with an absorption maximum deviation below 0.1 eV, allowing us to assign the underlying electronic transitions. We find the lowest optically active excited state to lie ca. 0.3 eV above the lowest TiO2 state. This state has a sizable contribution from the dye π* orbitals, strongly mixed with unoccupied TiO2 states. A similarly strong coupling is calculated for the higher-lying transitions constituting the visible absorption band centered at ca. 530 nm in the combined system. An ultrafast, almost instantaneous, electron injection component can be predicted on the basis of the strong coupling and of the matching of the visible absorption spectrum and density...
TL;DR: The femtosecond-resolved evolution of the emission spectrum of the important conjugated polymer poly(3-hexylthiophene) (P3HT) is presented in this article.
Abstract: The femtosecond-resolved evolution of the emission spectrum of the important conjugated polymer poly(3-hexylthiophene) (P3HT) is presented. Detailed fluorescence up-conversion spectroscopy was performed on P3HT solid-state films and on P3HT in chlorobenzene solution. Two excitation wavelengths and several emission wavelengths, covering the entire fluorescence spectrum, were used. The data were complemented by polarization-sensitive measurements. Our global analysis allowed a reconstruction of the time-resolved emission spectra with 200 fs temporal resolution, so that spectral changes due to the early relaxation processes following π–π* interband absorption in the pristine polymer could be comprehensively characterized. Absorption occurs in isolated polymer chains in solution and in the solid state (including interchain interactions) for the film. In both cases, we find evidence of delocalization of the electrons and holes formed in the energy bands directly after photoexcitation with excess energy. This i...
TL;DR: The first solution-processed depleted bulk heterojunction colloidal quantum dot solar cells are presented, which allows high absorption with full depletion, thereby breaking the photon absorption/carrier extraction compromise inherent in planar devices.
Abstract: The first solution-processed depleted bulk heterojunction colloidal quantum dot solar cells are presented. The architecture allows high absorption with full depletion, thereby breaking the photon absorption/carrier extraction compromise inherent in planar devices. A record power conversion of 5.5% under simulated AM 1.5 illumination conditions is reported.
TL;DR: In this paper, the influence of environmental factors on the degradation process of P3HT film has been investigated quantitatively, and the decay kinetics of the polymer absorption during variation of intensity and spectral distribution of the incident light, oxygen concentration, humidity level as well as temperature are monitored using infrared and UV/vis absorption spectroscopy.
Abstract: The influence of environmental factors on the degradation process of P3HT film has been investigated quantitatively. The decay kinetics of the polymer absorption during variation of intensity and spectral distribution of the incident light, oxygen concentration, humidity level as well as temperature are monitored using infrared and UV/vis absorption spectroscopy. Additionally, the oxygen diffusion into the polymer film has been investigated using fluorescence spectroscopy under the same experimental conditions. The degradation process is light initiated with a strong increase of the effectiveness toward the ultraviolet region of the spectrum. The observed photo oxidation is not oxygen diffusion limited although an activation energy of 26 kJmol−1 was observed for both degradation and oxygen diffusion. The observed kinetics, especially its dependence on wavelength of the incident light, point to a radical-based degradation process in the solid state rather than a singlet oxygen-based mechanism as it is obse...