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- 摘要
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Enhanced Absorption in MoS <sub/>2</sub> /Hg <sub/>0.33</sub> Cd <sub/>0.66</sub> Te Heterostructure for Application in Solar Cell Absorbers
摘要： The heterostructure of mercury cadmium telluride (Hg0.33Cd0.66Te) and monolayer MoS2 with Van der Waals (VdW) interaction is suggested for tuning the optical absorption in visible region. The calculations are performed using density functional theory (DFT). From the results, it is found that for molybdenum disulfide (MoS2) absorption is high in the ～390–430 nm range of visible region and for mercury cadmium telluride (Hg0.33Cd0.66Te) absorption is high in the ～310–350 nm. However, absorption in the MoS2/Hg0.33Cd0.66Te heterostructure increases with the wavelength and also shifts towards the red region of the visible spectrum, resulting into a well known red-shift phenomenon. Moreover, higher absorption is seen (entirely in visible region) in the heterostructure in the desired visible region range (λ ～640–710 nm) of the spectrum required for application in optoelectronic devices. The heterostructure results into semi-metallic or negligible indirect bandgap creation in contrast to direct bandgap observed in individual MoS2 and Hg0.33Cd0.66Te structures. The heterostructure can find application in Schottky barrier solar cell absorbers.
关键词： Optoelectronics,solar cells,transition metal dichalcogenides,absorption coefficient,refractive index
更新于2025-09-19 17:13:59
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Method of Laser Thermal Image Spectroscopy for Surface Diagnostics
摘要： A new method of laser-thermal imaging spectroscopy is presented and the results of studying samples with different absorption coefficients are reported. The times required for heating the surface of these samples by laser radiation with a wavelength of 0.634 μm to a temperature exceeding the initial value by 0.3°C are calculated and compared with the experimental data. The depths of laser-radiation penetration into the surface layer of the material under the condition of external and internal reflection are calculated. The depth determines the transition region in which the energy of absorbed laser radiation transforms into the thermal energy of the substance. It is shown that the method allows the surface of materials to be studied and zones with different optical and physical-chemical properties to be studied. The method can be used to solve problems in the field of medicine, surface restoration, forensic examination and others.
关键词： defect substance,surface defects,surface heating time,spectral absorption coefficient,penetration depth of laser radiation
更新于2025-09-19 17:13:59
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Terahertz intersubband transitions in GaAsBi/AlGaAs single quantum well heterostructure
摘要： GaAsBi/AlGaAs single quantum well conduction band structure, energy levels, and their corresponding wavefunctions have been calculated by solving the Schr?dinger equation. The influences of the heterostructure parameters on the intersubband transition (ISBT) frequency within the terahertz (THz) domain have been investigated. The results show that the quantum well width has a great impact on the THz ISBT frequency. In particular, an ISBT with a frequency of 2.611 THz (10.80?meV) has been obtained for specifically optimized parameters. The study of the intersubband optical absorption coefficient (OAC) was centered in the frequency band of 2 – 14 THz ( ~ 8 – 58 meV), therefore the corresponding results are useful for the optimization of THz detectors. Correspondingly, by changing the thickness of the active layer the number of the OAC peaks has been tuned. The dipole matrix element and the Fermi occupation function have been also studied in detail. Furthermore, the influences coming from the incidence angle on the OAC intensity were numerically investigated. The obtained results could be beneficial for the design and the optimization of devices operating in the THz frequency band.
关键词： GaAsBi quantum well,Terahertz region,Intersubband transitions,Optical absorption coefficient,Incidence angle,Active layer thickness
更新于2025-09-19 17:13:59
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What Is Limiting Pyrite Solar Cell Performance?
摘要： Iron pyrite (FeS2), an earth-abundant transition metal di-chalcogenide (TMD), has exotic electronic and optical properties suitable for solar cell applications. For example, it has an indirect band gap at (cid:1)0.95 eV and a direct band gap at 1.05–1.10 eV that is comparable to Si (1.1 eV), while absorption coef?cient of FeS2 is almost two orders of magnitudes higher than that of Si. Like Si, FeS2 solar cells also could have almost same theoretical energy conversion ef?ciency up to Shockley-Queisser limit. Additionally, the high absorption coef?cient of FeS2 offers the opportunities to fabricate a very thin absorber layer of thickness < 20 nm, which so far does not seem possible with other thin-?lm solar cell materials. It infers a sharp reduction of the production cost (￠/W) of electricity due to reduction of material cost. Consequently, FeS2 has gained interest as a potential non-toxic super absorber material in lieu of widely used but toxic and rare element containing CdTe and Cu(In, Ga)Se2 for thin-?lm solar cells.
关键词： super absorber,band gap,FeS2,solar cell,non-toxic,Iron pyrite,thin-film,absorption coefficient,photovoltaic
更新于2025-09-19 17:13:59
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Efficient absorption of laser light by nano-porous materials with well-controlled structure
摘要： The absorption of high-power nanosecond laser pulses in a porous matter is investigated through theoretical and numerical calculations. The effects of structural properties of the porous target such as size of pores and thickness of solid elements on the laser absorption are investigated. The time and space-dependent absorption coefficient of the laser created partially homogenized plasma is used in a plasma hydrodynamic code to reproduce the laser absorption and plasma formation processes in a porous matter. It is observed that the structural characteristics of the porous material can be optimized to significantly increase the laser energy absorption. For porous targets with pore sizes in the range 30–60 nm a value around 1000 nm could be desirable for the wall thickness to increase the laser absorption efficiency to more than 90%. The results can be advantageous in production of efficient laser absorber targets which are desirable in advanced applications such as inertial confinement fusion and laser-plasma x-ray sources.
关键词： laser produced plasma,laser–matter interaction,plasma absorption coefficient,porous targets
更新于2025-09-19 17:13:59
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: Why Sn substitution should be preferred to Pb vacancy for optimum solar cell efficiency
摘要： Methylammonium lead halide (MAPbI3) perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead toxicity, the role of Sn substitution and Pb vacancy (Pb-(cid:2)) are addressed in regulating stability and solar cell ef?ciency of MAPb1?X ?Y SnX (cid:2)Y I3 perovskite using hybrid density functional theory (DFT). The role of spin-orbit coupling (SOC) and the electron’s self-interaction error are examined carefully. We ?nd to reduce the Pb content from pristine MAPbI3, Sn substitution has a more favorable thermodynamic stability than creating Pb-(cid:2). Moreover, on substituting Sn, due to strong s-p and p-p couplings, the lower parts of the conduction band gets shifted downwards, which results in the reduction of the band gap (direct). This further helps us to get a high optical absorption coef?cient (redshifted) and maximum solar cell ef?ciency in MAPb1?X SnX I3 for 0 < X (cid:2) 0.5.
关键词： spin-orbit coupling,MAPbI3,solar cell efficiency,Pb vacancy,thermodynamic stability,Sn substitution,Methylammonium lead halide,hybrid density functional theory,optical absorption coefficient
更新于2025-09-19 17:13:59
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The effects of close packing and electric fields on the optical properties of three-dimensionally stacked quantum dots
摘要： An algorithm to evaluate the position of spherical quantum dots in a closely packed state inside a cube is presented and its accuracy confirmed numerically. A finite-difference method to solve the corresponding three-dimensional Schr?dinger equation in the presence of an external electric field is then described. The Arnoldi factorization method is used to diagonalize the resulting huge sparse matrix. The results reveal that both the intensity and direction of the electric field can significantly change the height of the absorption peak and are thus both important. Two different semiconducting structures, viz. GaAs/AlxGa1?xAs and InSb/GaSb, are investigated, revealing that the latter exhibits a more tunable absorption coefficient. The effect of the composition parameter x on the mentioned optical properties is also studied. The combination of this and earlier work indicates that photodetection in the wide range of 1.2–8.4 THz is possible. The proposed structure can thus be regarded as a possible candidate for use in photodetection devices in different fields of industries such as imaging, medicine, and materials characterization.
关键词： Close packing effect,Electric field,Finite difference method,Absorption coefficient,Three-dimensionally stacked quantum dots
更新于2025-09-16 10:30:52
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Standards, Methods and Solutions of Metrology || Third-Order Nonlinear Optical Properties of Quantum Dots
摘要： Quantum dots (QDs) are semiconducting nanocrystalline particles. QDs are attractive photonic media. In this chapter, we introduce third-order nonlinear optical properties and a brief idea about the physics of QDs. Z-scan technique and theoretical analysis adopted to obtain nonlinear parameters will be discussed. Analysis of third-order nonlinear optical parameters for PbS QDs suspended in toluene with radii 2.4 and 5.0 nm under different excitation beam power level and three different wavelengths (488, 514, and 633 nm) will be detailed. Third-order optical susceptibility χ(3) and optical-limiting behavior of PbS QD suspended in toluene are presented. Irrespective of their size, QDs are a good example of optical limiters with low threshold.
关键词： Z-scan technique,semiconductor,nonlinear absorption coefficient,third-order optical susceptibility,quantum dot,optical limiting,nonlinear optics,optical switching,nonlinear index of refraction
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - THz Time-Domain Reflection Spectroscopy of KTiOPO <sub/>4</sub>
摘要： Terahertz (THz) radiation has been of increasing interest in the last decades, for security, manufacturing, quality control, medical and security imaging applications. The field requires more efficient and affordable sources and nonlinear upconversion schemes point in this direction. KTiOPO, (KTP) is a well-established material for nonlinear optical applications in the visible and near-IR region thanks to its large transparency, high nonlinear coefficient and damage threshold. Its reasonably low absorption [1, 2] and strong polariton resonances [1] show promise for efficient IR to THz upconversion and Wu et al. [2] recently demonstrated its superiority to LiNbO3 and LiTaO3 in a back to back experiment. However, the complex refractive index needs to be measured before further power scaling is realistic. Terahertz time-domain spectroscopy (TTDS) allows for direct extraction of both the phase and amplitude of the THz electric field and grants the possibility of extracting the optical parameters n and α. In this work, we report on THz time-domain reflection spectroscopy of flux grown KTP from 0.5 to 7 THz at room temperature. The THz-TDS setup used air-filament plasma for generation of the THz radiation and the Pockel's effect in 300um thick GaP for detection. The a and b-axis of a KTP crystal were probed using an HDPE polarizer and rotation of the sample. The geometry of the setup is based on the work of Pashkin et al. [3], where the THz was focused onto the GaP crystal after the 25x15x0.5mm3 sample. Fig.1 shows the refractive index and the absorption coefficient from left to right, respectively. Blue and red color depict the two axes of the KTP crystal. Errors are estimated to: ?n < ±0.025 and ?α <±5 cm?1 (0.5?3THz), ?n < ±0.05 and ?α < ±25 cm?1 (3?5THz), ?n < ±0.1 and ?α < ±50 cm?1 (5?6THz), ?n < ± 0.25 and ?α < ±150 cm?1 (6?7THz). The accuracy in frequency was ≈ 90 GHz or 2 cm?1, limited by the scan time of 11ps. To the best of our knowledge, the convoluted frequency dependent nature of the refractive index has not been measured by direct time-resolved THz measurement before. Earlier spectroscopic studies of KTP have either lacked the possibility of directly extracting the complex refractive index [4] or been limited by absorption of the transmitted signal due to the strong resonances of KTP, limiting the bandwidth to about 2.5 THz [5]. In the regions where the bandwidth of this and older studies overlap, the measurements are similar, giving credibility to both measurements over the whole bandwidth. Besides, the measured resonances in Fig.1 can be related to IR active phonon modes, as seen in, e.g. [6]. This study will be of utmost importance when constructing new devices for optical to THz conversion. We also report a possible new phonon mode at 1.4 THz.
关键词： absorption coefficient,KTiOPO4,refractive index,THz time-domain spectroscopy,Terahertz
更新于2025-09-12 10:27:22
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Analysis of highly efficient perovskite solar cells with inorganic hole transport material
摘要： Organo-halide perovskites in planar heterojunction architecture have shown considerable promise as efficient light harvesters in solar cells. In this paper, a numerical modeling of a planar lead based perovskite solar cell (PSC) with Cu2ZnSnS4 (CZTS) as hole transporting material (HTM) has been done using one dimensional solar cell capacitance simulator (SCAPS-1D). The effects of numerous parameters such as defect density, thickness, and doping density of the absorber layer on the device performance are investigated. The doping densities and electron affinities of electron transporting material (ETM) and HTM are also varied to optimize the PSC performance. It has been observed that a thinner absorber layer of ~ 220 nm with a defect density of 1014 cm-3 compared to the reference structure improves the device performance. When doping density of the absorber layer increases beyond 2 × 1016 cm-3, the power conversion efficiency (PCE) reduces due to enhanced recombination rate. The defect density at the absorber/ETM interface reduces the PCE as well. Considering a series resistance of 5 Ωcm2 and all the optimum parameters of absorber, ETM and HTM layers simultaneously, the overall PCE of the device increases significantly. In comparison with the reference structure, the PCE of the optimized device has been increased from 12.76% to 22.70%, and hence the optimized CZTS based PSC is highly efficient.
关键词： CH3NH3PbI3,CZTS,SCAPS-1D,absorption coefficient
更新于2025-09-12 10:27:22