Broadband Absorption Enhancement Research Articles

Observation of broadband super-absorption of electromagnetic waves through space-time symmetry breaking

Using time as an additional design parameter in electromagnetism, photonics, and wave physics is attracting considerable research interest, motivated by the possibility to explore physical phenomena and engineering opportunities beyond the limits of time-invariant systems. Here, we report the experimental demonstration of enhanced broadband absorption of electromagnetic waves in a continuously modulated time-varying system, exceeding one of the key theoretical limits of linear time-invariant absorbers. This is achieved by harnessing the frequency–wave vector transitions and enhanced interference effects enabled by breaking both continuous space- and time-translation symmetries in a periodically time-modulated absorbing structure operating at radio frequencies. Furthermore, we demonstrate broadband coherent wave absorption using a secondary control wave, observing a nearly perfect, reconfigurable, antireflection effect over a broad continuous bandwidth. Our findings provide insights into enhanced wave absorption in time-varying scenarios and may enable the development of devices operating in a regime fundamentally beyond the reach of linear time-invariant systems.

Ray Tracing of Aluminum Nitride as Anti-Reflective Coating on Silicon for Photovoltaic Devices

III-nitride materials have attracted wide interests for optoelectronic and electronic applications due to their unique and tunable semiconducting and optical properties. Aluminum nitride (AlN) exhibits an ultra-wide bandgap of 6.2[Formula: see text]eV and wide transparency window from ultraviolet to mid-infrared, making it a promising candidate as an anti-reflective coating (ARC) material on silicon for photovoltaic (PV) devices. In this work, ray tracing is utilized to investigate the optical properties of AlN ARC on 150[Formula: see text][Formula: see text]m-thick c-Si absorber. AlN with thicknesses of 60–90[Formula: see text]nm are studied and the effects towards light absorption (within 300–1200[Formula: see text]nm wavelength region) and short-circuit current density ([Formula: see text] of the solar cell are analyzed. In the ray tracing, planar c-Si absorber without an ARC is used as a reference. The reference condition exhibits weighted average reflection (WAR) of 39.8% within the 300–1200[Formula: see text]nm wavelength region with [Formula: see text] of 25.49[Formula: see text]mA/cm2. AlN with 80[Formula: see text]nm is found to be the optimum ARC thickness, which leads to the enhanced broadband absorption with WAR of 19.7% within the spectral region. This thickness represents the highest [Formula: see text] achieved in this work (35.71[Formula: see text]mA/cm[Formula: see text].

Efficient Two-Stage Optimization for Enhanced Broadband Absorption of Higher-Order PML

Efficient Two-Stage Optimization for Enhanced Broadband Absorption of Higher-Order PML

All-dielectric ellipsoidal tetramer metasurface sensor with multi-resonances from the bound states in the continuum.

We demonstrate an all-dielectric tetramer metasurface that achieves high-precision refractive index sensing through the excitation of toroidal dipole, magnetic dipole, and electric quadrupole modes, driven by bound states in the continuum (BIC). The metasurface exhibits exceptional performance, with a quality factor of 4.65 × 104, a sensitivity parameter of 649 nm/RIU, and a figure of merit of 1.51 × 104 RIU-1, achieved by optimizing symmetry and lattice perturbations in periodic silicon tetramer ellipsoidal nanodisks on a SiO2 substrate. Additionally, the sensor effectively distinguishes analytes with extinction coefficient differences as small as 0.01 through enhanced broadband absorption. This innovation demonstrates substantial potential for label-free sensing applications in microfluidic chip integration.

A novel engineered sandwich composite with ceramic-coated graphite fibre-reinforced face sheets and an auxetic core for enhanced broadband electromagnetic absorption: design using multiscale computational analysis

Abstract A novel sandwich composite is designed for enhanced broadband absorption using a multiscale computational analysis. The sandwich panel is configured with BaTiO3 coated graphite fiber reinforced polymer (C-GFRP) composite, while BaTiO3 based auxetic material is used as the core material. A computationally efficient in-house tool based on the variational asymptotic method is used to homogenise the electromagnetic properties and evaluate the reflection loss characteristics of the proposed sandwich structure using the scattering matrices. A detailed parametric study of 300 analyses is conducted to identify the optimal sandwich panel configurations for achieving broadband reflection loss under the normal incidence of transverse electric (TE) and transverse magnetic (TM) polarised waves. Two different configurations have been obtained, satisfying the requirements of broadband reflection loss in the X-band frequency range. Configuration (a) Vf = 15% without any ceramic coating, and configuration (b) Vf = 20% with ceramic coating volume fraction (Cf) of 70%. Configuration (a) and (b) maintained the desired reflection loss of greater than -10 dB up to an incidence angle of 40◦ and 60◦, respectively. With the demonstrated capability of covering the entire broadband frequency range, the proposed configurations can serve as baselines to explore novel ceramic-based engineered composite architectures for broadband absorption applications.

Carrier mobility and broadband performance of two-dimensional Sb/SnSe van der Waals heterostructure: A first-principles study

Compared to single two-dimensional (2D) materials, stacking layered 2D materials with van der Waals (vdW) heterostructures offers novel opportunities to achieve desired exotic properties. Herein, 2D Sb/SnSe vdW heterostructure is constructed by vertically stacking the antimonene (Sb) monolayer on the tin selenide (SnSe) monolayer. We have conducted a theoretical study by using the first-principles calculations to comprehensively examine the electronic, optical, and mechanical properties. Phonon dispersion and ab initio molecular dynamics simulations have demonstrated that the Sb/SnSe vdW heterostructure possesses remarkable stability, ensuring its robustness up to 900 K. The Sb/SnSe vdW heterostructure is characterized as a semiconducting material with a direct band gap of 0.24 eV, calculated by the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional method. Compared to the pristine Sb and SnSe monolayers, the Sb/SnSe vdW heterostructure exhibits a lower work function value of 3.82 eV. Furthermore, the carrier mobility of the heterostructure demonstrates anisotropic characteristics with a notable improvement in hole-mobility (12.05 × 103 cm2V−1s−1) along the y-direction. The Sb/SnSe vdW heterostructure shows enhanced broadband absorption spectra, especially in the visible to near-infrared ranges. Our findings underscore the potential of the Sb/SnSe vdW heterostructure for future nano-electronic and optoelectronic technologies.

Broadband optical absorption enhancement in stacked MWCNTs array: towards new generation of solar cells

Broadband optical absorption enhancement in stacked MWCNTs array: towards new generation of solar cells

Optimal design of 3D macro-structures for multi-layer foams achieving ultra-broadband microwave absorption properties and high retention after immersion in brine

A novel flexible microwave absorbing material (C–MCM–FAS) with a cone-shaped sandwich structure is proposed, which is constructed by carbonyl iron-carbon nanotubes/PDMS foams and SiC–morchella biochar/PDMS film. To enhance broadband absorption properties, a three-level scale design has been creatively introduced into C–MCM–FAS, encompassing millimeter, micron and nano scales. The rational structural parameters of C–MCM–FAS are determined by CST simulation, leading to the preparation of C–MCM–FAS with an impressive minimum reflection loss (RLmin) of −43.26 dB and an effective absorption band (EB) covering the entire C2, X, and Ku bands at 11.79 GHz. Encouragingly, the measured results are basically consistent with the simulation results (an RLmin of −35.78 dB and an EB of 14.68 GHz), which verifies the accuracy of the theoretical simulation and the feasibility of the method. It holds great significance that the investigation of the adsorption retention rate of C–MCM–FAS after immersing it in 3.5 wt% NaCl solution for 21 days. The measured RLmin reaches −48.41 dB with a retention rate of 111.9 %, and the EB reaches 8.56 GHz with a retention rate of 72.6 %. This work presents a groundbreaking concept for designing structural absorbers, expecting the C–MCM–FAS to become a strong contender for application in special environments like microwave detection in the nautical field.

Broadband absorption enhancement in hole-transport-layer-free perovskite solar cell by grating structure

Broadband absorption enhancement in hole-transport-layer-free perovskite solar cell by grating structure

A periodic corrugated metallic nanomesh for broadband light absorption enhancement

Plasmonic nanostructures have been demonstrated for their application in thin film solar cells to enhance absorption. Of particular concern is the novel design, enabling the broadband absorption enhancement. Here, we proposed and implemented a periodic corrugated Au nanomesh for broadband light absorption enhancement. By combining plasmon treatment of pre-stretched substrate and nanosphere lithography, the Au nanomesh on the nanocorrugation with different period has been realized. Compared to the planar nanomesh, the periodic corrugated nanomesh exhibits observable absorption enhancement at broad wavelength range, especially from 700[Formula: see text]nm to 1000[Formula: see text]nm, which is of significance in bring solar energy up to more utilization due to poor absorption of thin film solar cells at the near-infrared band. The enhancement attributes to the spatially geometry deformation of nanomesh supported more plasmonic resonance at the different adjacent frequency. Also, the absorption enhancement is relative to the period of corrugation, which caused by the variation of geometry deformation amplitude of nanomesh. This periodic corrugated metallic nanomesh provides an alternative nanostructured electrode to broadband absorption enhancement for thin film solar cell application.

Plasmon-enhanced parabolic nanostructures for broadband absorption in ultra-thin crystalline Si solar cells.

Sub-wavelength plasmonic light trapping nanostructures are promising candidates for achieving enhanced broadband absorption in ultra-thin silicon (Si) solar cells. In this work, we use finite-difference time-domain (FDTD) simulations to demonstrate the light harvesting properties of periodic and parabola shaped Si nanostructures, decorated with metallic gold (Au) nanoparticles (NPs). The active medium of absorption is a 2 μm thick crystalline-silicon (c-Si), on top of which the parabolic nanotextures couple incident sunlight into guided modes. The parabola shape provides a graded refractive index profile and high diffraction efficiencies at higher order modes leading to excellent antireflection effects. The Au NPs scatter light into the Si layer and offer strong localized surface plasmon resonance (LSPR) resulting in broadband absorption with high conversion efficiency. For wavelengths (λ) ranging between 300 nm and 1600 nm, the structure is optimized for maximum absorption by adjusting the geometry and periodicity of the nanostructures and the size of the Au NPs. For parabola coated with 40 nm Au NPs, the average absorption enhancements are 7% (between λ = 300 nm and 1600 nm) and 28% (between λ = 800 nm and 1600 nm) when compared with bare parabola. Furthermore, device simulations show that the proposed solar cell can achieve a power conversion efficiency (PCE) as high as 21.39%, paving the way for the next generation of highly efficient, ultra-thin and low-cost Si solar cells.

Improving Photoelectric Conversion with Broadband Perovskite Metasurface.

The miniaturization and integration of optoelectronic devices require progressive size reduction of active layers, resulting in less optical absorption and lower quantum efficiency. In this work, we demonstrate that introducing a metasurface made of hybrid organic-inorganic perovskite (HOIP) can significantly enhance broadband absorption and improve photon-to-electron conversion, which roots from exciting Mie resonances together with suppressing optical transmission. On the basis of the HOIP metasurface, a broadband photodetector has been fabricated where photocurrent boosts more than 10 times in the frequency ranging from ultraviolet to visible. The device response time is less than 5.1 μs at wavelengths 380, 532, and 710 nm, and the relevant 3 dB bandwidth is over 0.26 MHz. Moreover, this photodetector has been applied as a signal receiver for transmitting 2D color images in broadband optical communication. These results accentuate the practical applications of HOIP metasurfaces in novel optoelectronic devices for broadband optical communication.

Enhanced Light Absorption and Efficient Carrier Collection in MoS2 Monolayers on Au Nanopillars.

We fabricated hybrid nanostructures consisting of MoS2 monolayers and Au nanopillar (Au-NP) arrays. The surface morphology and Raman spectra showed that the MoS2 flakes transferred onto the Au-NPs were very flat and nonstrained. The Raman and photoluminescence intensities of MoS2/Au-NP were 3- and 20-fold larger than those of MoS2 flakes on a flat Au thin film, respectively. The finite-difference time-domain calculations showed that the Au-NPs significantly concentrated the incident light near their surfaces, leading to broadband absorption enhancement in the MoS2 flakes. Compared with a flat Au thin film, the Au-NPs enabled a 6-fold increase in the absorption in the MoS2 monolayer at a wavelength of 615 nm. The contact potential difference mapping showed that the electric potential at the MoS2/Au contact region was higher than that of the suspended MoS2 region by 85 mV. Such potential modulation enabled the Au-NPs to efficiently collect photogenerated electrons from the MoS2 flakes, as revealed by the uniform positive surface photovoltage signals throughout the MoS2 surface.

Broadband absorption enhancement in carbon-based perovskite solar cell with a composite light trapping structure

In this work, a composite light-trapping strategy based on Ag@SiO2 nanoparticles embedded inside the active layer and an antireflection coating on the top surface is proposed to obtain broadband absorption improvement in carbon-based perovskite solar cells (C–PSCs). The effects of geometrical parameters, including the radius and period of Ag nanoparticles, the thickness of the protective SiO2 shell and the thickness of the antireflection coating, on the light absorption are investigated using the finite-difference time-domain (FDTD) method. Simulation results illustrate that nearly full absorption of light can be achieved with the optimized structure parameters for a 600 nm thick perovskite layer using the composite light-trapping scheme. The short-circuit current density (JSC) exhibits an improvement of 24.8% relatively compared to the C-PSC without light management. The proposed composite light-trapping structure allows improved light utilization and saved material consumption in C–PSCs.

Metalens array for InGaAs/InP avalanche photodiodes at optical-communication wavelengths

Reducing the dark current of InGaAs/InP avalanche photodiodes (APDs) is an important way to improve the performance of single-photon detection system. Therefore, the active region size of the APD is getting smaller and smaller to reduce the dark current, but that is based on sacrificing the quantum efficiency of the device. In this work, a metalens array is integrated with micro APD array, the metalens structure is proposed to converge light from tens of micrometers to several micrometers and form a focusing effect on the absorber layer to compensate for the loss of absorption efficiency due to the reduction in the size of the APD. The results show that the APD integrated with the metalens array structure behaves enhanced broadband absorption efficiency at optical-communication wavelengths. This design and proposed scheme offer the possibility of reducing the effective size of the APD to 2μm while improving broad-band optical response, owing to its light convergence capability.

Broadband absorption enhancement of metal-dielectric structures in the optical range and their application in solar energy storage

In this work, scattering properties of a metal-dielectric structure are carried out in the optical range. In the proposed structure design, the absorption coefficient reaches more than 80% and has an almost constant character in the entire visible spectrum. Based on the obtained simulation results, such structures can be utilized in the field of solar energy storage applications. A review of works in the field of plasmonic solar cells is given, where the efficiency is usually increased due to the confinement of incident radiation in the active region of photoelectric conversion using localized modes, which are concentrated at the surface of conducting nanoparticles. That is, such batteries are operated in narrow wavelength intervals. However, in this article, the assumed solar cell efficiency enhancement can be achieved by incorporating the entire optical range due to the proposed metamaterial structure.

Three-dimensional directional cellulose-based carbon aerogels composite phase change materials with enhanced broadband absorption for light-thermal-electric conversion

Energy shortage, environmental and ecological issues have prompted a focus on effective solar energy utilization. Using composite phase change materials (PCMs) as an energy storage medium is an important method to achieve efficient solar energy conversion. Biomass materials are highly desirable for solar applications due to their wide range of sources, low cost, environment-friendly, and natural porous structure. In this study, cellulose is selected as a carbon source precursor. Three-dimensional (3D) directional cellulose-based carbon aerogels (CBCA) are constructed through an immersion expansion, orientation, freeze-drying, and carbonization process. Taking tert-butanol/ deionized water as co-solvent, the aerogel shows high specific surface and productivity as well as low structural shrinkage. 3D directional graphitized porous network and graphene guarantee excellent broadband absorption, efficient heat transfer pathways, and effective thermal storage ability. Stearic acid (SA) and graphene are melt blending, followed by a vacuum-impregnating process for the formation of 3D composite PCMs. The thermal storage capability of PCMs is greater than 96%, accompanied by the highest thermal conductivity of 1.17 W/(m·K) with 0.5 wt% graphene. Moreover, the highest light-thermal conversion efficiency can reach 90.3%. It also has a maximum light-thermal-electric energy conversion output power of 1.80 mW. This work provides a feasible, economical strategy for highly efficient solar energy storage and thermal energy utilization.

Absorption Spectrum‐Compensating Configuration Reduces the Energy Loss of Nonfullerene Organic Solar Cells

AbstractUsing narrow bandgap nonfullerene acceptors (NFAs) can broaden the absorption spectrum of organic solar cells (OSCs) to the near‐infrared region. However, the simultaneously decreased extinction coefficient of the active layer at the blue region results in inevitable light escaping and energy loss. Herein, a blazed grating‐based device configuration consisting of a patterned rear electrode is employed to compensate for the low absorption of nonfullerene OSCs. Experimental results reveal that the normal incidence light, especially blue light, that bounces off the patterned rear electrode is concentrated in a large tilted angle and subsequently trapped in waveguide mode. Along with the excitation of surface plasmon polariton, the structured nonfullerene OSCs using a new‐designed PM6:M36 active layer obtain the broadband absorption enhancement with 1.5 times increase at the blue region. The optimized device achieves an 8.95% increase in photocurrent and a champion power conversion efficiency of approaching 18%, which is the highest reported value among all the devices based on A‐D‐A type NFAs.

Enhancement mechanisms of sub-bandgap broadband absorption in pyramid-structured silicon

Structure-engineered silicon exhibits a wealth of unique optical properties below its bandgap, which holds promise for mid-infrared and terahertz applications such as photodetection, thermophotovoltaics, radiative cooling, and spectroscopy. In this paper, we investigate enhancement mechanisms of sub-bandgap absorption of black silicon fabricated into periodic pyramids. Our measurements indicate that the pyramid structure leads to an enhanced broadband absorption in the wavelength region from 1.5 to 13.07 μm with an efficiency of over 80%. The broadband absorption enhancement is shown to originate from the Rayleigh–Wood anomaly, localized magnetic plasmonic resonance, and graded-index effect, which together facilitate the interaction between light and free-carriers in silicon. These results are helpful for understanding the interaction between light and black silicon.

Light absorption enhancement in ultrathin perovskite solar cells using light scattering of high-index dielectric nanospheres.

Arrays of high-index dielectric nanoparticles supporting both electrical and magnetic resonances have gained increasing attention for their excellent light-trapping (LT) effects, thus greatly improving the performance of ultrathin solar cells. This work explores front-located, high-index dielectric subwavelength nanosphere arrays as an efficient and broadband LT structure patterned on top of an ultrathin perovskite solar cell (PSC) for a greatly enhanced absorption. Combined strong light scattering and anti-reflection properties achieved by optimized geometrical parameters of the LT structure lead to a broadband absorption enhancement in the ultrathin thickness of a photoactive layer (100 nm) yielding the short-circuit current density (Jsc) of 18.7 mA/cm2, which is 31.7% higher than that of a planar counterpart. Moreover, effects of the LT structure on far-field radiation patterns, scattering cross-sections, multipoles' contributions, and asymmetry parameters along with the incidence angle and polarization dependence are investigated. The present strategy could be applied to diverse applications, such as other ultrathin or semitransparent solar cells, absorbers and photodetectors.