Complete Absorption Of Light Research Articles

Transition metal co-doped TiO2 nanotubes decorated with Pt nanoparticles on optical fibers as an efficient photocatalyst for the decomposition of hazardous gaseous pollutants

In this study, pristine TiO2 nanotubes (NTs) and Fe-, Ni-, Co- and Pt co-doped TiO2 NTs are synthesized via the hydrothermal method and photodecomposition of a mixture of NH3, CH4, and CO2 are investigated under simulated solar light irradiation. The physiochemical analysis confirms the formation of NTs and the stable oxidation state of co-doped TiO2 NTs. The photocatalytic activity analysis of the co-doped TiO2 NTs decorated with Pt shows superior performance compared to pure and Pt-doped TiO2 NTs which could be due to light absorption from the ultraviolet to the visible region and reduction of bandgap energy from 3.08 (TiO2) to 1.69 eV. Moreover, the nanostructures of co-doped TiO2 NTs/Pt NPs are coated on optical fibers which increase the efficiency of reactions by enabling complete light absorption revealing a synergistic improvement in the decomposition efficiency of the NH3 (95%), CO2 (60%), and CH4 (60%) in a mixture of gases.

Solar steam generation on scalable ultrathin thermoplasmonic TiN nanocavity arrays

Plasmonic-based solar absorbers exhibit complete light absorption in a sub-µm thickness, representing an alternative to mm-thick carbon-based materials most typically employed for solar-driven steam generation. In this work, we present the scalable fabrication of ultrathin plasmonic titanium nitride (TiN) nanocavity arrays that exhibit 90% broadband solar light absorption within ~ 250 nm from the illuminated surface and show a fast non-linear increase of performance with light intensity. At 14 Suns TiN nanocavities reach ~ 15 kg h –1 m –2 evaporation rate and ~ 76% thermal efficiency, a steep increase from ~ 0.4 kg h −1 m −2 and ~ 20% under 1.4 Suns. Electromagnetic, thermal and diffusion modeling of our system reveals the contribution of each material and reactor component to heat dissipation and shows that a quasi-two-dimensional heat dissipation regime significantly accelerates water evaporation. Our approach to ultrathin plasmonic absorbers can boost the performance of devices for evaporation/desalination and holds promise for a broader range of phase separation processes. • An ultrathin solar absorber based on TiN nanocavity arrays is introduced. • The material exhibits 90% broadband solar absorption within 250 nm. • The evaporation rate and the efficiency non-linearly increase with light intensity. • An extensive multi-physics modeling supports the experimental findings. • A quasi-two dimensional heat dissipation regime is theoretically discussed.

Principles of co‐axial illumination for photochemical reactions: Part 1. Model development

AbstractPhotochemical reactors with conventional homogeneous illumination suffer from a light efficiency problem, which is inherent to their design: Dark zones arise near the reagent‐rich inlet whereas the reagent depleted outlet is over‐illuminated. Any attempt to mitigate dark zones at the inlet will only increase photon losses further downstream. This study reports the principles and model equations for co‐ and counter‐current illumination in photochemical reactors, along with an optimization study to determine the most efficient and productive operating point. This work proves that the use of co‐ and counter‐current illuminated reactors increases the energy efficiency while easing scalability by implementing larger path lengths, without altering the reactor's geometry. We report a simple model to determine the conversion obtained by such novel illumination techniques and compare it to the current state‐of‐the‐art. Two nondimensional groups where derived that describe all possible reactor configurations, these are the initial absorbance (A) and the quantum photon balance (ρϕ). Variation of both parameters leads for noncompetitive photochemical reactions to an optimal point for the current state‐of‐the‐art as well as the novel co‐axial illumination. Ultimately, we recommend the use of an initial absorbance value (A) of at least 1, and a quantum photon balance (ρϕ) equal to 1 to introduce sufficient light and enable near complete absorption of light.

Thermally Durable Nonfullerene Acceptor with Nonplanar Conjugated Backbone for High‐Performance Organic Solar Cells

AbstractA nonfullerene acceptor (NFA) with acceptor–donor–acceptor (A–D–A) architecture, i‐IEICO‐2F, based on 4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene as an electron‐donating core and 2‐(6‐fluoro‐2,3‐dihydro‐3‐oxo‐1H‐inden‐1‐ylidene)‐propanedinitrile as electron‐withdrawing end groups, is designed and synthesized. i‐IEICO‐2F has a twist structure in the main conjugated chain, which causes blueshifted absorption and leads to harmonious absorption with a high bandgap donor. The bandgap of i‐IEICO‐2F compliments the bandgap of suitable wide bandgap donor polymers such as J52, leading to complete light absorption throughout the visible spectrum. Devices based on i‐IEICO‐2F exhibit optimized photovoltaic performance including an open‐circuit voltage of 0.93 V, a short‐circuit current density of 16.61 mA cm−2, and a fill factor of 73%, and result in a power conversion efficiency (PCE) of 11.28%. The i‐IEICO‐2F‐based devices reach PCEs of >11% without using any additives or post‐treatments. Devices are found to be thermally stable and maintain 44% of their initial PCE after 184.5 h of continuous thermal annealing (TA) treatment at 150 °C. Based on UV, atomic force microscopy (AFM), and grazing incidence wide angle X‐ray scattering (GIWAXS) results, i‐IEICO‐2F devices show almost identical morphology and molecular orientation throughout the TA treatment and excellent stability compared to other IEICO derivatives.

Structure and pigment make the eyed elater’s eyespots black

Surface structures that trap light leading to near complete structural absorption creates an appearance of “super black.” Well known in the natural world from bird feathers and butterfly scales, super black has evolved independently from various anatomical structures. Due to an exceptional ability to reduce specular reflection, these biological materials have garnered interest from optical industries. Here we describe the false eyes of the eyed elater click beetle, which, while not classified as super black, still attains near complete absorption of light partly due to an array of vertically-aligned microtubules. These cone-shaped microtubules are modified hairs (setae) that are localized to eyespots on the dorsum of the beetle, and absorb 96.1% of incident light (at a 24.8° collection angle) in the spectrum between 300–700 nm. Filled with melanin, the setae combine structure and pigment to generate multiple reflections and refractions causing light to travel a greater distance. This light-capturing architecture leaves little light available to receivers and the false eyes appear as deep black making them appear more conspicuous to predators.

Ultra-Broadband and Omnidirectional Perfect Absorber Based on Copper Nanowire/Carbon Nanotube Hierarchical Structure

Zero reflection and complete light absorption are required in a wide range of applications ranging from sensing devices to solar heaters and photoelectrodes. However, simultaneously satisfying the ...

Solar harvesting based on perfect absorbing all-dielectric nanoresonators on a mirror.

The high-index all-dielectric nanoantenna system is a platform recently used for multiple applications, from metalenses to light management. These systems usually exhibit low absorption/scattering ratios and are not efficient photon harvesters. Nevertheless, by exploiting far-field interference, all-dielectric nanostructures can be engineered to achieve near-perfect absorption in specific wavelength ranges. Here, we propose - based on electrodynamics simulations - that a metasurface composed of an array of hydrogenated amorphous silicon nanoparticles on a mirror can achieve nearly complete light absorption close to the bandgap. We apply this concept to a realistic device, predicting a boost of optical performance of thin-film solar cells made of such nanostructures. In the proposed device, high-index dielectric nanoparticles act not only as nanoatennas able to concentrate light but also as the solar cell active medium, contacted at its top and bottom by transparent electrodes. By optimization of the exact geometrical parameters, we predict a system that could achieve initial conversion efficiency values well beyond 9% - using only the equivalent of a 75-nm thick active material. The device absorption enhancement is 50% compared to an unstructured device in the 400 nm - 550 nm range and more than 300% in the 650 nm - 700 nm spectral region. We demonstrate that such large values are related to the metasurface properties and to the perfect absorption mechanism.

Nanostructured gold films exhibiting almost complete absorption of light at visible wavelengths

Nanostructured metal surfaces have been known to exhibit properties that deviate from that of the bulk material. By simply modifying the texture of a metal surface, various unique optical properties can be observed. In this paper, we present a simple two step electrochemical process combining electrodeposition and anodization to generate black gold surfaces. This process is simple, versatile and up-scalable for the production of large surfaces. The black gold films have remarkable optical behavior as they absorb more than 93% of incident light over the entire visible spectrum and also exhibit no specular reflectance. A careful analysis by scanning electron microscopy reveals that these unique optical properties are due to their randomly rough surface, as they consist in a forest of dendritic microstructures with a nanoscale roughness. This new type of black films can be fabricated to a large variety of substrates, turning them to super absorbers with potential applications in photovoltaic solar cells or highly sensitive detectors and so on.

Growth of mixed K2(Ni,Co)(SO4)2·6H2O crystals under stationary conditions of supercooling and forced convection of the aqueous solution

The technique and the scheme of the system for growing single crystals, including complex mixed composition, under stationary conditions of supercooling and forced convection of aqueous solution were described. Solubility in water of various compositions of K2CoxNi1−x(SO4)2·6H2O (KCNSH) and the dependence of Co content in the KCNSH crystal of Co concentration in the saline part of aqueous solutions of KCNSH have been measured in the temperature range of 30–70°C. It was found that the growth sectors {001} and {110} differ in Ni and Co contents. The Ni/Co ratio is dependent on the value of solution supersaturation. The optical transmission spectra of crystals grown showed high transmittance in the UV region of the spectrum and the almost complete absorption of light in the visible spectrum. It is concluded that the crystals grown can be used as efficient UV filters.

Dispersion Topological Darkness at Multiple Wavelengths and Polarization States

Complete suppression of reflection is in principle achievable in ideal optical systems with unique optical features including complete light absorption, abrupt phase change, etc. However, conventional optical systems have an extremely tight tolerance on fabrication errors or inherent roughness of thin films or patterns. Therefore, it is difficult to realize the perfect reflectionless condition in practice. To overcome this challenge, a “topological darkness” concept with mild restrictions to the film quality is proposed using periodic metallic patterns and self‐assembled core–shell particles. Due to the topological effect, the robust nature of reflectionless surfaces is improved dramatically even in the presence of imperfections. Here the “mild” restriction will be further broken to realize reflectionless thin film systems using directly deposited thin films or random metal nanoparticles. Moreover, a broad absorption band is achieved by tuning the effective optical constants of the top absorbing layer. Remarkably, compared with conventional reflectionless phenomena under single polarization states and wavelengths, the system can realize multiwavelength zero‐reflection points for both polarization states on the same chip. These proof‐of‐concept results pave the way toward the development of practical applications using abrupt phase change and complete light absorption for label‐free optical sensing and enhanced light‐matter interaction within ultrathin film systems.

Employing ZnS as a capping material for PbS quantum dots and bulk heterojunction solar cells

Formation of bulk heterojunctions by incorporating colloidal quantum dots into a mesoporous substrate is anticipated to yield efficient charge collection and complete light absorption. However, it is still challenging in view of the bulky nature of the colloidal quantum dots and the ex situ deposition route. In this study, the feasibility of employing ZnS as a capping material for PbS quantum dots is dissected by carefully designed control experiments, with reference to the formation of bulk heterojunctions by successive ionic layer adsorption and reaction (SILAR) at ambient conditions. The results reveal that the underlying ZnS layer facilitates the PbS deposition by an ion exchange process, while the overlaying ZnS layer tends to cover the PbS in a manner similar to a physical stacking process. Therefore, PbS quantum dots capped with amorphous ZnS are developed with the SILAR technique, which could be used to fill up the mesoporous substrates and thus construct bulk heterojunctions. The hole collection is the limiting factor of such bulk heterojunction solar cells, as demonstrated by inserting a conductive polymer layer in the control devices. Further development of the quantum dot system is discussed in consideration of the fundamental issues presented in this study.

Experimental demonstration and modeling of the internal light scattering profile within solar cells due to random dielectric scatterers

Many photovoltaic technologies are shifting toward thin-film devices to simultaneously reduce costs and improve carrier collection efficiencies; however, the need for nearly complete light absorption within the semiconductor to achieve large short-circuit currents constrains this thickness reduction. Light trapping strategies can be employed to increase absorption in thinner devices. Random scattering coatings offer a simple, cost-effective way to increase solar cell absorption without the drawback of increased surface recombination or reduced bandwidth that occurs when using surface texturing or gratings. However, coatings that show excellent performance as scatterers in free space generally do not enhance device absorption as much as an ideal Lambertian scatterer. Here, we present an experimental technique and theoretical model that accurately describes the absorption improvement that is achievable with coatings based on random ensembles of dielectric scatterers. We find that the ideal Lambertian model substantially overestimates the experimental scattering results, but significant path length enhancements are still achievable. The experimental techniques presented here should enable the testing of various optical models that attempt to surpass the ray optics light trapping limit, which have in many cases been hindered by the experimental difficulty of coupling the incident light into the optical modes of the absorber.

Core-Shell CdS-Cu₂S Nanorod Array Solar Cells.

As an earth-abundant p-type semiconductor, copper sulfide (Cu2S) is an attractive material for application in photovoltaic devices. However, it suffers from a minority carrier diffusion length that is less than the length required for complete light absorption. Core-shell nanowires and nanorods have the potential to alleviate this difficulty because they decouple the length scales of light absorption and charge collection. To achieve this geometry using Cu2S, cation exchange was applied to an array of CdS nanorods to produce well-defined CdS-Cu2S core-shell nanorods. Previous work has demonstrated single-nanowire photovoltaic devices from this material system, but in this work, the cation exchange chemistry has been applied to nanorod arrays to produce ensemble-level devices with microscale sizes. The core-shell nanorod array devices show power conversion efficiencies of up to 3.8%. In addition, these devices are stable when measured in air after nearly one month of storage in a desiccator. These results are a first step in the development of large-area nanostructured Cu2S-based photovoltaics that can be processed from solution.

Review of Plasmonic Nanocomposite Metamaterial Absorber.

Plasmonic metamaterials are artificial materials typically composed of noble metals in which the features of photonics and electronics are linked by coupling photons to conduction electrons of metal (known as surface _lasmon). These rationally designed structures have spurred interest noticeably since they demonstrate some fascinating properties which are unattainable with naturally occurring materials. Complete absorption of light is one of the recent exotic properties of plasmonic metamaterials which has broadened its application area considerably. This is realized by designing a medium whose impedance matches that of free space while being opaque. If such a medium is filled with some lossy medium, the resulting structure can absorb light totally in a sharp or broad frequency range. Although several types of metamaterials perfect absorber have been demonstrated so far, in the current paper we overview (and focus on) perfect absorbers based on nanocomposites where the total thickness is a few tens of nanometer and the absorption band is broad, tunable and insensitive to the angle of incidence. The nanocomposites consist of metal nanoparticles embedded in a dielectric matrix with a high filling factor close to the percolation threshold. The filling factor can be tailored by the vapor phase co-deposition of the metallic and dielectric components. In addition, novel wet chemical approaches are discussed which are bio-inspired or involve synthesis within levitating Leidenfrost drops, for instance. Moreover, theoretical considerations, optical properties, and potential application of perfect absorbers will be presented.

Interband phototransitions involving free electrons: III. Transmission of light through crystals

It has been shown that the two-electron mechanism of nonlinear optical absorption considered in the first two parts of our study, even at laser radiation intensities j ∼ 103-104 W/cm2 in the case of nanosecond pulses, can lead to almost complete absorption of light by crystals that are transparent to weak radiation of the same wavelength. A number of materials that can exhibit the considered effects have been described.

Self-modulation of ultra-fast laser pulses with 1550 nm central wavelength in VO2 thin films

The possibility to use an ultra-fast laser operating at 1550 nm wavelength to induce intensity self-modulation in metal-insulator phase transition VO2 thin films was investigated. The results show that a self-modulation value upto 0.55 can be obtained by using z-scan method. In comparison, an externally triggered phase transition induced by heating the sample produced a modulation depth of 0.995 corresponding to almost complete light absorption. The results suggest that significant self-modulation can be produced by fs laser pulses, but the modulation strength is partially suppressed by incomplete transition from a transparent to an absorbing state and potentially time delay in the rise of absorbance.

Plasmon resonance tuning in metallic nanocavities

Nanocavities fabricated in a metallic surface have important and technologically useful properties of complete light absorption and strong field enhancement. Here, we demonstrate how a nanometerthick alumina deposition inside such a cavity can be used to gain an exquisite control over the resonance wavelength. This process allows achieving a precise control over the spectral response and is completely reversible allowing many tuning attempts to be made on a single structure until the optimum performance is achieved.

Complete light absorption in graphene-metamaterial corrugated structures

We show that surface-plasmon polaritons excited in negative permittivity metamaterials having shallow periodic surface corrugation profiles can be explored to push the absorption of single and continuous sheets of graphene up to 100%. In the relaxation regime, the position of the plasmonic resonances of the hybrid system is determined by the plasma frequency of the metamaterial, allowing the frequency range for enhanced absorption to be set without the need of engineering graphene.

Collective behavior of impedance matched plasmonic nanocavities

Nanometer sized cavities arranged as a subwavelength metallic grating can provide omni-directional and complete absorption of light. We present an explanation of this extraordinary phenomenon as a collective resonant response of a system based on a surface impedance model. This model gives a straightforward way to design systems for optimum light trapping performance and as well gives fundamental insights into the interaction of light with metals at the nanoscale.

Complete absorption in a heterostructure composed of a metal and a doped photonic crystal

We theoretically demonstrate that complete absorption of light can be realized in a heterostructure composed of a thick metal film and truncated photonic crystals with a lossy dielectric defect. Because of the coupling between the interface mode and the defect mode, all of the light can enter the heterostructure. Meanwhile, the fields are enhanced remarkably in the defect, so the light is fully absorbed by the lossy defect. When the coupling between two different localized modes is strong, two absorption peaks are obtained, while a weak coupling leads to a narrow absorption band due to the degeneracy of two localized modes.