Significant Absorption Enhancement Research Articles

Significant Enhancement of Absorption and Luminescence Dissymmetry Factors in the Far-Red Region: A Zinc(II) Homoleptic Helicate Formed by a Pair of Achiral Dipyrromethene Ligands.

A homoleptic zinc(II) helicate organized by a pair of achiral dipyrromethene ligands through zinc(II) coordination was synthesized to evaluate the chiroptical properties. This zinc complex showed strong exciton-coupled chiroptical responses from the helical configuration with a large absorption dissymmetry factor |gabs | (up to 0.20). More importantly, intense polarized luminescence in the far-red region (700-850 nm) with a fluorescence quantum yield ΦFL of 0.23 was observed for this helicate with a dissymmetry factor |glum | of 0.022, the largest value among rare-earth- and precious-metal-free small molecules. These unprecedentedly large g values were supported by theoretical calculations.

Optical materials: Studying the role of hetropolyacid to enhance the nonlinear optical responses of porphyrin in their hybrids system

Nonlinear optical responses are measured to investigate the role of hetropolyacid (HPA) in porphyrin-Lindqvist type {∼PM@HPA} hybrid systems, {where PM@HPA = [(TBA)8{(MTPPN4)(Mo6O18)4}]; M = 2H (1) and Mn (2)}. The well-known Z-scan technique with wavelength (λ) = 532 nm and pulse duration of τ = 6 ns is used. The results clearly show the significant enhancement in nonlinear self-defocusing effect and reverse saturable absorption under closed and open-aperture configuration for PM@HPA hybrids. It is also observed that the second hyperpolarizability γ values, {1 (4.639 × 10−29 esu) < 2 (5.214 × 10−29 esu)}, are directly proportional to the discrepancy of LUMO level (ΔE) values {1 (2.214 eV) < 2 (2.339 eV)} while they are inversely proportional to the HOMO−LUMO energy gap Eg values {1 (2.003 eV) > 2 (1.862 eV)} in the PM@HPA hybrid system where the porphyrin moiety acts as electron donor whilst HPA acts as electron acceptor. Therefore, the emergence of a facile electron transformation from the porphyrin moieties to the low-lying LUMO levels of HPA is mainly responsible for the enhancement in nonlinear optical responses of PM@HPA hybrids system. As a consequence the hybrid compounds can be fascinating for optical limiting applications.

Constraining Aging Processes of Black Carbon in the Community Atmosphere Model Using Environmental Chamber Measurements.

The direct radiative forcing of black carbon aerosol (BC) on the Earth system remains unsettled, largely due to the uncertainty with physical properties of BC throughout their lifecycle. Here we show that ambient chamber measurements of BC properties provide a novel constraint on the crude BC aging representation in climate models. Observational evidence for significant absorption enhancement of BC can be reproduced when the aging processes in the four‐mode version of the Modal Aerosol Module (MAM4) aerosol scheme in the Community Atmosphere Model version 5 are calibrated by the recent in situ chamber measurements. An observation‐based scaling method is developed in the aging timescale calculation to alleviate the influence of biases in the simulated model chemical composition. Model sensitivity simulations suggest that the different monolayer settings in the BC aging parameterization of MAM4 can cause as large as 26% and 24% differences in BC burden and radiative forcing, respectively. We also find that an increase in coating materials (e.g., sulfate and secondary organic aerosols) reduces BC lifetime by increasing the hygroscopicity of the mixture but enhances its absorption, resulting in a net increase in BC direct radiative forcing. Our results suggest that accurate simulations of BC aging processes as well as other aerosol species are equally important in reducing the uncertainty of BC forcing estimation.

Synthesis of Ag-Loaded TiO2 Electrospun Nanofibers for Photocatalytic Decolorization of Methylene Blue

Titanium dioxide (TiO2) is one of the excellent photocatalysts used for degradation of environmetal pollutants. In this work, 2.5, 5.0 and 7.5 wt.% of silver (Ag)-loaded TiO2 nanofibers of mean size 52–134 nm were synthesized by electrospinning method. These electrospun nanofibers were calcined at 500 °C to enable the transformation of Rutile (R) phase to Anatase (A), elimination of reaction moieties from the TiO2 matrix and subsequently formation of Ag clusters. The effect of Ag loading on the morphology, crystal structure, phase transformation, and band gap of these electrospun nanofibers have been characterized by scannining electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), raman spectroscopy and UV-visible spectroscopy. These nanofibers exhibited a red-shift in the absorbance edge and a significant enhancement of light absorption in the wavelength range of 250–550 nm. These electrospun nanofibers were investigated for photodecomposition of methylene blue (MB), and photocatalytic decolorization rates were determined by pseudo-first-order equation. The rate constants for the pure and those of 2.5, 5.0, and 7.5 wt% Agloaded TiO2 nanofibers were computed to be 0.1439 min-1, 0.1608 min-1, 0.1876 min-1, and 0.2251 min-1 respectively.

Wavelength stability in a hybrid photonic crystal laser through controlled nonlinear absorptive heating in the reflector

The need for miniaturized, fully integrated semiconductor lasers has stimulated significant research efforts into realizing unconventional configurations that can meet the performance requirements of a large spectrum of applications, ranging from communication systems to sensing. We demonstrate a hybrid, silicon photonics-compatible photonic crystal (PhC) laser architecture that can be used to implement cost-effective, high-capacity light sources, with high side-mode suppression ratio and milliwatt output output powers. The emitted wavelength is set and controlled by a silicon PhC cavity-based reflective filter with the gain provided by a III–V-based reflective semiconductor optical amplifier (RSOA). The high power density in the laser cavity results in a significant enhancement of the nonlinear absorption in silicon in the high Q-factor PhC resonator. The heat generated in this manner creates a tuning effect in the wavelength-selective element, which can be used to offset external temperature fluctuations without the use of active cooling. Our approach is fully compatible with existing fabrication and integration technologies, providing a practical route to integrated lasing in wavelength-sensitive schemes.

Enhanced absorption in monolithic perovskite/CuInGaSe2 tandem solar cells with double surface-engineered nanostructures

The development of perovskite solar cells has approached the theoretical efficiency limitation for single junction device geometry. To break this single junction efficiency limitation, it is highly desirable to construct a tandem structure in which the high bandgap perovskite is stacked with a current commercial prevailing low bandgap CuInGaSe2 (CIGS) solar cell. Improving the bottom CIGS subcell absorption with a reduced thickness for photocurrent matching holds the key to developing a high-performance perovskite/CIGS tandem device and reducing the overall manufacturing cost. We propose a monolithic perovskite/CIGS tandem solar cell integrated with optimized nanophotonic structures: dielectric nanocones on the top surface and Ag nanoparticles at the rear surface. Significant light absorption enhancement as large as 12.5% is achieved with a reduced bottom cell thickness by 58.7% through simulation. This approach opens up a viable pathway for achieving high-performance and cost-effective perovskite/CIGS tandem solar cells.

Rational design of cobalt and nitrogen co-doped carbon hollow frameworks for efficient photocatalytic degradation of gaseous toluene

In this work, the hollow Co/N co-doped carbon frameworks (Co/N-C) were successfully constructed by in situ transformation of zeolitic imidazolate frameworks (ZIF-67) through polycondensation of dopamine. The hollow and porous structure of Co/N-C was demonstrated by transmission electron microscopy (TEM). The doping and Co-N-C active sites were verified by X-ray photoelectron spectroscopy (XPS). The UV–vis diffusion reflectance spectra (UV–vis DRS) of hollow Co/N-C nanoparticles reflected a significant enhancement of optical absorption in the range of 300–800 nm. With hollow porous structure, strong optical absorption and rich Co-N-C active sites, the Co/N-C exhibited a high photocatalytic performance by using gaseous toluene as a model pollutant, and the degradation efficiency of gaseous toluene was found to be around 78.2% under mild conditions (i.e., Temperature = 273 K, Pressure = 1 atom, λ ≥ 420 nm, t = 6 h). The photocatalytic degradation process and mechanism of toluene were further investigated by in situ Fourier transform infrared (FTIR) spectroscopy, which indicated that multiple hydroxylation and benzen ring opening are both involved in the catalytic elimination processes, and the initial intermediate species including benzaldehyde and benzoic acid were firstly derived from the hydroxylation due to the hydroxyl radical followed by further oxidation into carbon dioxide and water.

Defect-engineered TiO2 Hollow Spiny Nanocubes for Phenol Degradation under Visible Light Irradiation

Herein, we mainly report a strategy for the facile synthesis of defect-engineered F-doped well-defined TiO2 hollow spiny nanocubes, constructed from NH4TiOF3 as precursor. The topological transformation of NH4TiOF3 mesocrystal is accompanied with fluorine anion releasing, which can be used as doping source to synthesize F-doped TiO2. Our result shows that the introduction of oxygen vacancies (Vo’s) and F dopant can be further achieved by a moderate photoreduction process. The as prepared sample is beneficial to improve photocatalystic degradation and Photoelectrochemical (PEC) efficiency under visible light irradiation. And this improvement in photocatalytic and photoelectrocatalytic performance can be ascribed to the significant enhancement of visible light absorption and separation of excited charges resulted from the presence of oxygen vacancies, F− ions and hollow structure of TiO2.

Preparation and comparative evolution of mechanical behavior of Fe and Fe2O3 foams and their polymer composites

The open cell foams with reticulated structure are cellular materials which is gaining interest in the recent past not only because of scientific interest but also because of their technological importance. By the virtue of their inherent properties derived out of their unique structure, made them promising and rather indispensable materials for wide range of applications. Some of the examples are structural parts, aerospace components, filters, energy absorbing, insulation, catalysis, heat exchangers and energy absorption. In the present investigation, highly porous reticulated open cell iron oxide (Fe2O3) and iron (Fe) foams are successfully fabricated by polymeric sponge replication process. In order to explore the possibility to enhance the energy absorption capability of this cellular materials, Fe2O3 and Fe foams prepared in this study are encapsulated and infiltrated with epoxy polymers which have exhibited an enhancement of weight by 1.45–1.90 times as compare to bare foams. These composite specimens are being metallic/ceramic skeletons with second phase as epoxy polymer on encapsulation/infiltration are expected to fail under stresses with unique mechanisms. This substantially enhances the energy absorption though extend of weight increase is not significant. The bare and composite foam samples were evaluated for quasistatic compression and dynamic impact behavior under identical conditions. On compression, a significant enhancement in energy absorption of 42 and 90 times for Fe2O3 and a less prominent enhancement of 1.3 and 1.95 times in case Fe foams are observed on encapsulation and infiltration respectively. Under dynamic impact an enhancement in energy absorption of 4 and 11 times in case of Fe2O3 and for Fe foam 6.3 and 20.6 times are observed on encapsulation and infiltration respectively. It is evident that energy absorption property is a strong function of material of fabrication, epoxy phase and stress type and conditions. The current study demonstrates an effective way to enhance the mechanical properties of ceramic (Fe2O3) and metallic (Fe) cellular foams through epoxy polymer encapsulation/infiltration process though infiltration have exhibited significant increase in both cases.

Development of Domperidone Solid Lipid Nanoparticles: In Vitro and In Vivo Characterization.

Domperidone (DOP) is extensively applied orally in the management of nausea and vomiting. Upon oral administration, its bioavailability is very poor due to its poor solubility in alkaline media. Therefore, the aim of this work was to investigate DOP-loaded solid lipid nanoparticles (DOP-SLNs) in order to sustain its release pattern and to enhance oral bioavailability. DOP-SLNs were prepared using four different lipids. Prepared DOP-SLNs were characterized for "polydispersity index (PDI), particle size, zeta potential, % entrapment efficiency (% EE), and drug release behavior." Differential scanning calorimetry (DSC) study was carried out to illustrate the physical form of DOP and excipients. The morphology of DOP-SLNs was confirmed by scanning electron microscopy (SEM). Pharmacokinetic study on optimized DOP-SLN in comparison to tablet was performed in rats. The "particle size, PDI, zeta potential, and % EE" of optimized formulation (F5) were recorded as 201.4nm, 0.071, - 6.2mV, and 66.3%, respectively. DSC thermograms suggested amorphous state of DOP in various SLNs. Surface morphology of SLNs using SEM suggested spherical shape of the nanoparticles within nanometer size range. In vitro release studies confirmed that all SLN formulations possessed a sustained release over a period of 12h (51.3% from optimized formulation) in comparison with immediate release from conventional tablets (100% after 90min). Pharmacokinetic study showed significant enhancement in oral absorption of DOP from optimized SLN in comparison with DOP tablet. The enhancement in relative bioavailability of DOP from optimized SLN was 2.62-fold in comparison with DOP tablet.

Design and analysis of an ultra‐thin crystalline silicon heterostructure solar cell featuring SiGe absorber layer

Here, the authors studied a silicon-germanium (Si 1-x Ge x ) absorber layer for the design and simulation of an ultra-thin crystalline silicon solar cell using Silvaco technology computer-aided design. Seeking ways to design and fabricate solar cells using 100 μm thicker silicon substrates is the subject of intense research efforts among the photovoltaic (PV) community. The aim is to further reduce the substrate thickness to 20 μm without compromising the efficiency of the solar cell. A thin layer of SiGe film with the Ge composition of 15% has been introduced in this work that assists in absorbing the longer wavelength of the sunlight spectrum. The effects of the doping concentration and absorber layer thickness on the conversion efficiency have been examined. The simulated results exhibited significant enhancement in the sunlight absorption as compared to the reference structure based on crystalline silicon. The highest efficiency of 16.8% with an overall solar cell thickness of ~26 μm has been observed. The proposed heterostructure solar cell design will support the industrial development of an efficient, low-cost, shorter energy payback time, and light-weight PV technology for its widespread implementation.

Improving light trapping of polymer solar cell via doping a new array of triple core-shell spherical nanoparticles utilizing realistic modeling

The local surface plasmon resonance (LSPR) effects of metallic nanoparticles (such as light scattering and giant local field) in organic materials can improve the optical absorption capability of organic solar cells. This is especially important for polymer solar cells where the active layer thickness has been limited (<150 nm) due to short electron-hole diffusion length. LSPR effects depend on the features of nanoparticle, such as shape and size. Qua cubic nanoparticle produces a stronger LSPR compared to other shapes and increased LSPR effect increases the light absorption. However, fabrication of the cubic nanoparticle is much more difficult compared to fabrication of spherical ones. This study aims to increase LSPR effects of spherical nanoparticles and we propose the SiO2@Au@SiO2 new structure for them. Our simulation results demonstrate increase in power absorption and short circuit current of ∼103% and ∼118%, respectively, with square array of SiO2@Au@SiO2 nanoparticles with central nanoparticle inserted in thin active layer compared to the structure without nanoparticles. Subsequently, we propose the new square array without central nanoparticle for SiO2@Au@SiO2 nanoparticles. Calculations show significant enhancement in power absorption and short circuit current of respectively ∼136% and ∼154%, compared to the structure without nanoparticles. These improvements are justified pursuant to enhanced light trapping inside the active layer.

Light trapping in ultrathin CuIn1-xGaxSe2 solar cells by dielectric nanoparticles

In this work, light trapping effects based on dielectric nanoparticles (NPs) are numerically evaluated in ultrathin CuIn1-xGaxSe2 (CIGSe) solar cells for different locations of NPs, cell architectures and illumination directions, with relevant implications and optimized NP parameters being specified. The severe absorption in Mo is the main constraining factor for the effective implementation of light trapping NPs in ultrathin CIGSe cells. For a significant light absorption enhancement, it is favoured to integrate dielectric NPs at the rear interface of CIGSe/back contact and employ transparent conductive oxide (TCO) back contacts rather than the conventional Mo. It is demonstrated, that under front illumination, the low-index (n = 1.5) hemispherical NPs at the CIGSe/TCO interface cause significant light trapping effects. The NP-patterned ultrathin cells achieve a maximum short circuit current density (Jsc) of 36.4 mA/cm2 at an upper limit of 500 nm CIGSe thickness, which is as high as 94% Jsc of their thick flat counterparts with a CIGSe thickness of 2000 nm. In contrast, under back illumination, the patterned ultrathin cells realize comparable absorption to the corresponding thick counterpart at a CIGSe thickness of only 300 nm and the maximum Jsc (35.2 mA/cm2) saturates at a CIGSe thickness of 425 nm. Further, Jsc is less attenuated by the parasitic absorption in Al:ZnO (AZO) under back illumination than under front illumination in module configuration, where a much thicker AZO is required. This suggests that patterned ultrathin CIGSe solar cells under back illumination will be a promising cell architecture simultaneously for high efficiencies and less material usage in industrial module production.

Significant enhancement of light absorption in undoped graphene using dielectric multilayer system

The interband optical conductivity of undoped graphene gives only 2.3% absorption of light regardless of the light frequency. In this work, we show that by enhancing the electric field on a graphene surface through the interference effect, the light absorption of an undoped monolayer graphene can be much enhanced up to 50%. The monolayer graphene is put at the center of a specially designed multilayer structure of dielectric media. The enhanced absorption can be achieved for any arbitrary frequency by changing the number of layers or the refractive index of the layers. We also show that the absorption of light is used by Joule's heating of graphene which can be applied for local heating by light.

Enhanced ultraviolet photo-response in Dy doped ZnO thin film

In the present work, a Dy doped ZnO thin film deposited by the spin coating method has been studied for its potential application in a ZnO based UV detector. The investigations on the structural property and surface morphology of the thin film ensure that the prepared samples are crystalline and exhibit a hexagonal crystal structure of ZnO. A small change in crystallite size has been observed due to Dy doping in ZnO. AFM analysis ascertains the grain growth and smooth surface of the thin films. The Dy doped ZnO thin film exhibits a significant enhancement in UV region absorption as compared to the pure ZnO thin film, which suggests that Dy doped ZnO can be used as a UV detector. Under UV irradiation of wavelength 325 nm, the photocurrent value of Dy doped ZnO is 105.54 μA at 4.5 V, which is 31 times greater than that of the un-doped ZnO thin film (3.39 μA). The calculated value of responsivity is found to increase significantly due to the incorporation of Dy in the ZnO lattice. The observed higher value of photocurrent and responsivity could be attributed to the substitution of Dy in the ZnO lattice, which enhances the conductivity, electron mobility, and defects in ZnO and benefits the UV sensing property.

Tuning the nonlinear optical absorption in Au/BaTiO3 nanocomposites with gold nanoparticle concentration

We report on the nonlinear optical absorption coefficient of Au/BaTiO3 nanocomposite films and its dependence on gold nanoparticle concentration. Au/BaTiO3 nanocomposite films with different molar ratio of Au/Ba are prepared by sol-gel technique and characterized by X-ray diffraction, UV Visible absorption spectroscopy and high resolution transmission electron microscopy. An open aperture Z-scan technique is employed to study the third order nonlinear optical properties of Au/BaTiO3 thin films. An Nd:YAG laser operating at 532 nm wavelength having a pulse width of 5 ns is used for the measurements. The two-photon absorption coefficient of the films increases linearly with gold nanoparticle concentration and significant enhancement of nonlinear optical absorption is observed. This ability to fine tune the nonlinear optical coefficients of Au/BaTiO3 films would be handy in optical device applications.

A simple hydrazone as a multianalyte (Cu2+, Al3+, Zn2+) sensor at different pH values and the resultant Al3+ complex as a sensor for F.

A new colorimetric and fluorescence molecular chemosensor based on triazole hydrazone can be used as a multi-probe for selective detection of Al3+, Zn2+, and Cu2+ by monitoring changes in the absorption and fluorescence spectral patterns. Results show that Al3+ and Zn2+ ions can induce remarkable fluorescence enhancement at pH 6.0 and pH 10.0, respectively, while the addition of Cu2+ ions leads to a significant UV-visible absorption enhancement in the visible range at pH 6.0. In addition, the resultant Al3+ complex could act as an ‘on–off’ fluorescence sensor for F−. The fluorescence sensor was also used to monitor intracellular Al3+, Zn2+, and F− in Hela cells.

Engineering intermediate-band photovoltaic material by heavily co-doping selenium and nitrogen in silicon

Among the various dimer configurations, the substitutional dimer exhibits the lowest formation energy and can form an impurity band that overlaps with the conduction band. The impurity band turns into an isolated and partially filled intermediate-band in the bandgap when the two impurity atoms are separated from a dimer to the remotest distance. The configurations with different impurity atom distances are stable in the Si material owing to their constant formation energy and can lead to a significant enhancement of the optical absorption in the infrared wavelength range.

Design of dual-frequency electromagnetic wave absorption by interface modulation strategy

Design of highly efficient electromagnetic wave (EMW) absorbing materials with continuous dual-absorption peaks is a hot topic but a challenge in anti-electromagnetic interference and pollution fields. Herein, we developed an interfacial modulation strategy to achieve this goal in dielectric nanocomposite and clarified the interface function and relevant mechanism. Experimentally, CuS/Ag2S composite with tunable heterointerface was fabricated by decorating Ag2S nanoparticles on CuS flakes via cation-exchange reaction. By changing the Ag2S loading, the heterointerface between Ag2S and CuS induced strong dielectric resonant peak and improved impedance matching, which resulted in the significant enhancement of EMW absorption and the appearance of continuous dual-absorption peaks in CuS/Ag2S composite. With a rather low filler loading of 20 wt% and a thin layer thickness of 2.89mm, the optimized CuS/Ag2S composite exhibited continuous dual-absorption peaks with reflection losses of −47.2 and −20.6 dB, respectively. The proposed interfacial modulation strategy may potentially be used to fabricate other highly efficient dual-absorption absorbers.

Key Points in the Latest Developments of High‐Efficiency Thin‐Film Silicon Solar Cells

Thin‐film silicon has been intensively used in photovoltaic applications. In recent years, most of the record efficiencies in thin‐film silicon solar cells have been updated frequently, particularly in microcrystalline silicon solar cells. In this article, key points in the latest developments of high‐efficiency thin‐film silicon solar cells are reviewed with a short overview of thin‐film silicon technology. The main driver for the efficiency improvement of microcrystalline silicon cells was the development of sophisticated light scattering substrates. The well‐designed honeycomb‐textured substrates enabled a systematic and detailed optimization to realize the growth of high‐quality films and significant light absorption enhancement simultaneously. The knowledge obtained about microcrystalline silicon solar cells and the insights regarding light‐induced degradation of a‐Si:H solar cells were successfully transferred to triple junction cells, which was demonstrated by the achievement of the record stabilized efficiency of 14%.