Thin Absorber Research Articles

An Empirical Model for Optimizing the Sound Absorption of Single Layer MPP Based on Response Surface Methodology

Micro-perforated panel (MPP) is a thin panel absorber capable of absorbing sound energy at a targeted frequency range by adjusting the MPP parameters. An analytical model is available, but it is not a direct, convenient method for practitioners to de

Coherently Time-Varying Metasurfaces

Known coherent metasurfaces control the interference of waves of a given frequency with other coherent waves at the same frequency, either illuminating from a different direction or created as intermodulation products. In this paper, we introduce a class of metasurfaces that are modulated in time coherently with the illuminating radiation. Such modulation opens a possibility to control reflection, absorption, and transmission at multiple frequencies, including illuminations by two or more incoherent waves. In particular, we study dynamic resistive layers and show how to use them to design thin multifrequency perfect absorbers that overcome the bandwidth limit for static linear absorbers. Furthermore, we demonstrate possibilities of remote tuning of the absorption level. We hope that this work opens up alternative avenues in wave engineering using coherent modulation of metasurface parameters.

Impact of HTM on lead-free perovskite solar cell with high efficiency

The Scaps-1d simulator was used to simulate a lead-free perovskite CH3NH3SnI3 based solar cell devices fabricated from different hole transport materials (HTM). This research looks at two organic and two inorganic HTM layers. The cell structure used in this study is FTO/TiO2/CH3NH3SnI3/HTM (variable)/Au(variable). Spiro-OMeTAD, PEDOT:PSS, CuO and Cu2O are the HTM materials used. The results show that utilizing CuO as an HTM produces better outcomes than other HTMs, with an efficiency of 28.45%. The thickness, acceptor concentration (NA), and defect density (Nt) of the perovskite layer on optoelectronic properties of the solar cell are focus of simulation studies. According to this study, an perovskite layer thickness of 1000 nm is suitable for a decent photovoltaic cell. Furthermore, by adjusting the HTM thickness and the defect density of HTM and absorber layer, promising findings of Jsc of 34.38 mAcm−2, Voc of 1.011 V, FF of 80.85% and PCE of 28.10% were obtained for Spiro-OMeTAD based PSC. Finally, in order to improve the device's performance, an anode material with high work function is required. Our findings reveal that using a thin absorber layer results in low photo generated charge carriers due to less absorption, but high carrier extraction. Although more carriers are created in the cell due to increased absorption, decreased collection efficiency is related to recombination, which decreases Voc for thick perovskite layers. Device efficiency is improved by increasing the doping density up to 1018 cm−3 in the perovskite layer due to built-in electric field across the solar cell. Again a very thin or thick HTL is not ideal for high PCE. For low recombination and a high fill factor, an HTM (Spiro-OMeTAD) of 1–100 nm is necessary. The great power conversion efficiency of organic HTM based lead-free PSC brings up the new possibilities for obtaining renewable energy.

Ultrabroadband Rectangular Double Split Ring Based Perfect Solar Absorber

Metasurfaces could be very beneficial when elaborating solar cells to succeed in balancing between cost and efficiency. Thus, thin absorbers achieving high performance are attainable with the possibility to use any material. In this work, a perfect absorber based on a tungsten (W) metal-insulator-metal (MIM) metasurface is proposed. The MIM array consists of a rectangular double split ring resonator (RD-SRR) pattern with a specific set of parametric values that maximize the structure’s absorption. The study results in an ultrabroadband absorption over a minimum value of 97.02% and reaching a high peak of 99.9%. Its integrated absorption over the entire spectral solar at AM1.5 is 99.6%. This absorber fulfills efficiently solar devices’ requirements including the ability to work under high temperature conditions afforded by the use of tungsten.

Mode-locked ytterbium-doped fiber laser with zinc phthalocyanine thin film saturable absorber

A stable mode-locked laser was demonstrated using a newly developed zinc phthalocyanine (ZnPc) thin film as passive saturable absorber (SA) in ytterbium-doped fiber laser (YDFL). The ZnPc thin film was obtained using a casting method and then inserted between the two fiber ferrules of a YDFL ring cavity to generate mode-locked pulses. The resulting pulsed laser operated at a wavelength of 1034.5 nm having a repetition rate of 3.3 MHz. At pump power of 277 mW, the maximum output power and pulse energy are achieved at 4.92 mW and 1.36 nJ, respectively. ZnPc has a high chemical and photochemical stability, and its significance for use as a potential SA in a mode-locked laser is reported in this work.Graphical

Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging

Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging

Synthesis of tetragonal copper-nickel ferrite decorated nitrogen-doped reduced graphene oxide composite as a thin and high-efficiency electromagnetic wave absorber

The development of graphene-based magnetic composites with strong absorption, wide bandwidth and thin thickness remains a great challenge. In this work, nitrogen-doped reduced graphene oxide/copper-nickel ferrite (NRGO/Cu0.5Ni0.5Fe2O4) composite was fabricated via a one-step hydrothermal process. Results demonstrated that the microscopic morphology and electromagnetic (EM) absorbing performance of as-synthesized magnetic composites were greatly influenced by the type and composition of spinel ferrites. Significantly, the attained NRGO/Cu0.5Ni0.5Fe2O4 composite showed a good dispersion of particles, and a large number of tetragonal Cu0.5Ni0.5Fe2O4 nanoparticles were almost homogeneously loaded on the rippled and wrinkled surfaces of lamellar NRGO. Compared with NRGO/CuFe2O4 and NRGO/NiFe2O4 composites, the NRGO/Cu0.5Ni0.5Fe2O4 composite presented the notably enhanced EM absorbing performance. It was noteworthy that the optimal minimum reflection loss reached up to − 67.4 dB and maximum effective absorption bandwidth achieved 4.7 GHz under a very thin matching thickness of 1.7 mm and a filler loading content of 50 wt%. Furthermore, the possible EM dissipation mechanism had been proposed. The results of this work would provide a reference for the development of RGO-based composites as thin and high-performance EM wave absorbers.

Numerical study of nSi and nSiGe solar cells: Emerging microstructure nSiGe cell achieved the highest 8.55% efficiency

This paper reports about the comparative study of nSi and nSiGe microstructure materials opto-electrical energy conversion prospect. The significance of nSiGe thin active laye in organic-inorganic heterojunction (HJ) solar cell efficiency progression is illustrated. Transparent and carrier selective top contact purposes p-type un-doped organic materials are promising for low processing cost n-Si HJ solar cell. Near infrared band absorption enrichment by Ge inclusion in n-Si thin active layer is a new design approach. p-PTAA/n-Si PV device modelling and it electrical properties are investigated by using SCAPS simulator. Thin Si active layer solar cell is commercially important. However, thin layer absorption related technological shortcoming overcoming approaches 10% Ge content impact is studied in this work. Moreover, SiO2 nanomaterial passivated p-PTAA/SiO2/n-SiGe and p-PTAA/SiO2/n-Si models active layer thickness and operating temperature effects have also been studied. The current-voltage (J-V) characteristics analysis is realized that nSiGe cell is potential for the progression of current density and efficiency. SiO2 nanomaterial passivated 3 μm SiGe microstructure cell is realized promising to increase 48.1 mA/cm2 of current density. The highest 8.55% efficiency is achieved for 2 nm SiO2 passivation and 20 nm of PTAA emitter.

Active and Smart Terahertz Electro-Optic Modulator Based on VO2 Structure.

Modulating terahertz (THz) waves actively and smartly through an external field is highly desired in the development of THz spectroscopic devices. Here, we demonstrate an active and smart electro-optic THz modulator based on a strongly correlated electron oxide vanadium dioxide (VO2). With milliampere current excitation on the VO2 thin film, the transmission, reflection, absorption, and phase of THz waves can be modulated efficiently. In particular, the antireflection condition can be actively achieved and the modulation depth reaches 99.9%, accompanied by a 180° phase switching. Repeated and current scanning experiments confirm the high stability and multibit modulation of this electro-optic modulation. Most strikingly, by utilizing a feedback loop of "THz-electro-THz" geometry, a smart electro-optic THz control is realized. For instance, the antireflection condition can be stabilized precisely no matter what the initial condition is and how the external environment changes. The proposed electro-optic THz modulation method, taking advantage of strongly correlated electron material, opens up avenues for the realization of THz smart devices.

Multi-components matching manipulation of MXene/PPy@β2-SiW11Co/Fe3O4 nanocomposites for enhancing electromagnetic wave absorption performance

Two-dimensional layered metal carbides (MXene) have a broad application prospect in electromagnetic absorption, but suffer from poor impedance matching, which limits the absorbing performance. Herein, an efficient nanocomposite absorber was successfully prepared via loading Co-substituted β2-keggin-type polyoxometalate doped with polypyrrole and Fe3O4 on the surface of MXene. Polyoxometalate and HCl as a proton acid doped polypyrrole, with anions attached to the main chain, could adjust the electromagnetic parameters, making the nanocomposites material easily achieve the best conductivity and impedance matching; Fe3O4 introduced magnetic loss, and the freedom of movement of Fe2+ and Fe3+ caused multiple polarization; dipole polarization was induced by defects, dipoles and dangling bonds in nanocomposites; the charge accumulated at the three phase interface and led to interfacial polarization. We had conducted research on the absorbing properties of nanocomposites with different as-prepared unitary to ternary products, loading rates and component proportion. When the filling level was 45 wt%, an optimal reflection loss value of MXene/PPy@β2-SiW11Co/Fe3O4 nanocomposites at only 1.7 mm reached up to −62.6 dB, and the effective absorption bandwidth of 9 GHz could be obtained at the low thickness range of 1.5–2.9 mm. These results demonstrated that the prepared nanocomposites wereexpected to be a promising electromagnetic wave absorber with thin thickness and high absorption intensity.

Ultrathin 3D radial tandem-junction photocathode with a high onset potential of 1.15 V for solar hydrogen production

Combining a progressive tandem junction design with a unique Si nanowire (SiNW) framework paves the way for the development of high-onset-potential photocathodes and enhancement of solar hydrogen production. Herein, a radial tandem junction (RTJ) thin film water-splitting photocathode has been demonstrated experimentally for the first time. The photocathode is directly fabricated on vapor-liquid-solid-grown SiNWs and consists of two radially stacked p - i - n junctions, featuring hydrogenated amorphous silicon (a-Si:H) as the outer absorber layer, which absorbs short wavelengths, and hydrogenated amorphous silicon germanium (a-SiGe:H) as the inner layer, which absorbs long wavelengths. The randomly distributed SiNW framework enables highly efficient light-trapping, which facilitates the use of very thin absorber layers of a-Si:H (~50 nm) and a-SiGe:H (~40 nm). In a neutral electrolyte (pH = 7), the three-dimensional (3D) RTJ photocathode delivers a high photocurrent onset of 1.15 V vs. the reversible hydrogen electrode (RHE), accompanied by a photocurrent of 2.98 mA/cm 2 at 0 V vs. RHE, and an overall applied-bias photon-to-current efficiency of 1.72%. These results emphasize the promising role of 3D radial tandem technology in developing a new generation of durable, low-cost, high-onset-potential photocathodes capable of large-scale implementation. A radial tandem junction thin-film photocathode with a V onset of 1.15 V vs. RHE has been demonstrated directly on VLS-grown SiNWs for the first time, using a-Si:H (~50 nm) as the outer absorber layer and a-SiGe:H (~40 nm) as the inner layer.

Precisely nanostructured HfO2 rear passivation layers for ultra‐thin Cu(In,Ga)Se2

AbstractThe quest for material‐efficient Cu(In,Ga)Se2 (CIGS) solar cells encourages the development of ultra‐thin absorbers. Their use reduces material consumption and energy usage during production by increasing the throughput. Thereby, both the bill of materials as well as the energy and capital costs are reduced. However, because thin absorbers are prone to increase back contact recombination, back surface passivation schemes are necessary to reach a similar or higher conversion efficiency than for absorbers with conventional thickness. Here, we investigate nanostructured hafnium oxide (HfO2) rear passivation layers for ultra‐thin CIGS solar cells. We fabricate regular arrays of point contacts with 200 nm diameter through HfO2 layers with thicknesses between 7 and 40 nm using electron beam lithography and reactive ion etching. The current–voltage curves of solar cells with a 500 nm thick CIGS absorber layer and the nanostructured passivation layer show improved performance concerning Voc and Jsc compared to non‐passivated reference devices. Furthermore, external quantum efficiency and optical reflection confirm an effective passivation behavior, with an average efficiency increase of up to 1.2% for the cells with the 40 nm thick HfO2 layer. In addition, simulation work shows that even 40 nm thick HfO2 passivation layers have only a minimal effect on the optical properties of ultra‐thin CIGS solar cells, and hence, the photocurrent increase verified experimentally stems from electrical improvements caused by the HfO2 layer passivation effect. We also investigate the impact of ultra‐thin (0.3, 0.6, 1.3, and 2.5 nm) non‐patterned HfO2 passivation layers on the same type of solar cells. However, these results showed no improvement in solar cell performance, despite an increase in the current density with layer thickness.

Structural and component optimization of conventional magnetic material Co to synthesis dendritic-like FeCo and rose-like CoNi toward high-performance electromagnetic wave absorption

To promote the electromagnetic (EM) wave absorption property of conventional magnetic material Co, we synthesized dendritic-like FeCo and rose-like CoNi by a hydrothermal process. The morphology, structure and magnetic properties results reveal that dendritic-like FeCo is consisted of leaf-like unit layers and rose-like CoNi is composed of nano-sheets, and all samples have ferromagnetic behavior. The absorption intensity of dendritic-like FeCo to EM wave can achieve −36.5 dB at 1.0 mm absorber thickness and the effective absorption bandwidth (EAB) of rose-like CoNi is 5.3 GHz at 1.5 mm absorber thickness, which are far better than conventional magnetic material Co. The EM wave absorption mechanisms reveal that favourable impedance matching, multiple reflection and absorption to EM wave in the unique structure promote dendritic-like FeCo and rose-like CoNi show an excellent EM wave absorption capacity at thin absorber thickness. As a result, excellent EM wave absorbing materials can be obtained by optimizing the composition and structure of Co, and this design strategy can also be used to improve the EM wave absorbing properties of other conventional magnetic materials.

Manufacturing of a Magnetic Composite Flexible Filament and Optimization of a 3D Printed Wideband Electromagnetic Multilayer Absorber in X-Ku Frequency Bands.

With the multiplication of electronic devices in our daily life, there is a need for tailored wideband electromagnetic (EM) absorbers that could be conformed on any type of surface-like antennas for interference attenuation or military vehicles for stealth applications. In this study, a wideband flexible flat electromagnetic absorber compatible with additive manufacturing has been studied in the X-Ku frequency bands. A multilayer structure has been optimized using a genetic algorithm (GA), adapting the restrictions of additive manufacturing and exploiting the EM properties of loaded and non-loaded filaments, of which the elaboration is described. After optimization, a bi-material multilayer absorber with a thickness of 4.1 mm has been designed to provide a reflectivity below −12 dB between 8 and 18 GHz. Finally, the designed multilayer structure was 3D-printed and measured in an anechoic chamber, achieving −11.8 dB between 7 and 18 GHz. Thus, the development of dedicated materials has demonstrated the strong potential of additive technologies for the manufacturing of thin wideband flexible EM absorbers.

Thin film absorber selection to pair with silicon for 1-Sun tandem photovoltaics

We present a photon-counting simulation to evaluate the impact of top cell film quality on overall performance when designing stack tandem photovoltaic devices. We apply this model to the case where the bottom cell material is silicon in order to take advantage of the relatively low cost of manufacture already available. For the top cell, we approach material selection with an understanding that thin-film devices usually can’t reach the output voltage ideality that can be achieved with optimized single crystal devices. With limited thickness for the top cell, a range of photons with energies higher than the band gap may still not be absorbed in the top cell due to the normally smaller absorption coefficients just above the bandgap energy. We use the Tauc formalism for parameterizing near-edge optical absorption and investigate the effects of film thickness and bandgap on expected efficiency values of CdTe and MALI family materials, which are already known to be good candidates for top cell thin-film devices.

An MMC-based cryogenic calorimeter with a massive sodium molybdate crystal absorber for neutrinoless double beta decay searches

Sodium molybdate crystals are excellent scintillating target material that can be used to investigate the neutrinoless double beta decay of 100Mo.Because this material contains Na nuclei, it could also be used to clarify the contribution of Na in the controversial claim of dark matter observation by the DAMA/LIBRA experiment.Recent developments have allowed the growth of sodium molybdate crystals of several hundred grams, which makes it possible to build large scale experiments.Therefore, a cryogenic calorimeter with a crystal of significant mass, which can exploit the excellent energy resolution from thermal signals and particle identification using the scintillation signals,is highly desired. We have developed a cryogenic calorimeter with a cylindrical sodium molybdatecrystal of 178 g with dimensions of 4 cm (height) × 4 cm (diameter) coupled to a metallic magnetic calorimeter (MMC).The detector was also equipped with a light detector with a thin Ge absorber to detect scintillation signals.The detector test measurements showed excellent energy resolution and particle discrimination using dual detection of heat and light signals,and thus demonstrate that the crystal is a promising tool for searching for rare phenomena events. Details of the detector development with the massive sodium molybdate crystal are discussed in this paper along with the performance results from test measurements.

Metal-organic framework-derived hierarchical porous carbon fiber bundles/Y2Co8Fe9 composite as a thin and broadband electromagnetic wave absorber

The development of broadband and thin electromagnetic wave absorbing materials is urgently required for use in practical applications. In this study, microwave absorption composites comprising Y2Co8Fe9 and various weight ratios of metal-organic framework (MOF)-derived carbon fiber bundles (0%, 0.1%, 0.3%, 0.5%) were prepared. The composite filled with 0.1 wt% MOF-derived carbon fiber bundles had a minimum reflection loss (RL) of -64.79 dB at a thickness of 1.44 mm and an effective absorption bandwidth (with an RL of less than -10 dB) of 5.02 GHz. Furthermore, a wide effective absorption bandwidth of 6.52 GHz was also acquired at 1.6 mm. The microwave absorption performance was significantly enhanced owing to the improved impedance matching, as well as the synergetic effect between the dielectric loss and magnetic loss. This study provides a new paradigm for fabricating composites consisting of MOF-derived materials and rare-earth materials for thin and broadband microwave absorption performance.

Achieving broad absorption bandwidth of Ba2Co2Fe12O22 ferrites by adjusting the sintering temperature

The Ba2Co2Fe12O22 (Co2Y) ferrites were prepared via the sol–gel method, and the dielectric and magnetic properties were tuned by changing sintering temperature (Ta). It can be noted that the nature resonance frequency of Co2Y decreases form 10.2 GHz to 1.9 GHz with increasing sintering temperature, and the resonance peaks ascribed to exchange coupling between Fe2+ ions and Fe3+ ions appear in 13–17 GHz. Due to the synergy of Fe2+ ions and oxygen vacancies, the real part of complex permittivity (ε′) of Co2Y ferrites decreases firstly, and then increases with increasing sintering temperature. The excellent microwave absorption properties are obtained at Ta = 1100 °C, its effective absorption bandwidth (EAB) reaches 7.3 GHz at a thickness of only 1.4 mm. The outstanding properties are mainly ascribed to a combination of multiple reflections, dipole polarization, natural resonance, exchange resonance and good impedance matching. Our research provides an efficient approach for obtaining the thin and broadband microwave absorbers by adjusting the sintering temperature of Co2Y ferrites.

Insights into Cu2O thin film absorber via pulsed laser deposition

Cuprous oxide materials are of growing interest for optoelectronic devices and were produced by several chemical and physical methods. Here, we report on the structural, optical, and electrical properties of CuxO thin films prepared by the pulsed laser deposition technique. The substrate temperature, as well as the oxygen partial pressure in the deposition chamber, were varied to monitor the copper to oxygen ratio within the deposited films. The growth conditions were carefully optimized to provide the highest conductivity and mobility. Thus, 100 nm thick cuprous oxide films (Cu2O) deposited at 750 °C exhibited a resistivity of 16 Ω∙cm, high mobility of 30 cm2/(V∙s), and a bandgap of around 2 eV. The film deposited at the optimized deposition parameters on Nb:STO (001) substrate with Au top electrode showed a photovoltaic response with an open circuit voltage of 0.56 V. These results path the way to efficient solar cells made with Cu2O films via the pulsed laser deposition technique.

Cation disorder engineering yields AgBiS2 nanocrystals with enhanced optical absorption for efficient ultrathin solar cells

Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27 mA cm−2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions.