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Electronic and optical properties of double perovskite oxide Pb2ScMO6 (M = Ta, Sb) using a first principles approach
摘要： In this study, the electronic and optical properties of the double perovskite (DP) oxides Pb2ScMO6 (M = Sb, Ta) were systematically investigated using the full-potential linearized augmented plane wave model. Calculations were performed using both the generalized gradient approximation and modified Becke–Johnson potentials. The results showed that the O-atom is responsible for the maxima in the density of states (DOS) in the valence band, whereas the Sc-atom contributes to the maximum DOS in the conduction band. The dielectric constants, absorption coefficients, and reflectivity were also calculated for these systems. The results indicated the presence of wide band gaps in both of these DPs, thereby indicating their insulating semiconducting nature.
关键词： photon energy,energy,dielectric,double perovskite,density of states,band gap
更新于2025-09-23 15:23:52
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Toward Efficient Triple-Junction Polymer Solar Cells through Rational Selection of Middle Cells
摘要： The photon energy losses of polymer solar cells (PSCs) routinely drag their experimental power conversion efficiencies (PCEs) far below the theoretical limits. We report herein efficient triple-junction PSCs (TJ-PSCs) with mitigated energy losses through rational selection of subcells. We reveal that avoiding strong photon competition between the front and middle cells is critical in balancing the absorption rate among subcells with realistic layer thicknesses. Efficient TJ-PSCs are achieved by stacking a front cell of PBDB-T-2F:PC71BM, a middle cell of PBDB-T:HF-TCIC, and a rear cell of PTB7-Th: IEICO-4F in series and connecting them with two functional interconnection layers. A PCE of 13.09% is obtained from champion devices, representing one of the best TJ-PSCs among the reported studies. It accounts for a 35% improvement in efficiency over those of single-junction PSCs with the same absorption range, which is mainly attributed to the reduced nonabsorbing and thermalization losses of TJ-PSCs.
关键词： polymer solar cells,photon energy losses,power conversion efficiencies,nonfullerene acceptors,triple-junction
更新于2025-09-23 15:21:01
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Photon energy response optimization using few-channel spectroscopy dose method for Si-PIN photodetector applied in personal dose equivalent measurements
摘要： Si-PIN photodetectors having features such as low cost, small size, low weight, low voltage, and low power consumption are widely used as radiation detectors in electronic personal dosimeters (EPDs). The technical parameters of EPDs based on the Si-PIN photodetectors include photon energy response (PER), angular response, inherent error, and dose rate linearity. Among them, PER is a key parameter for evaluation of EPD measurement accuracy. At present, owing to the limitations of volume, power consumption, and EPD cost, the PER is usually corrected by a combination of single-channel counting techniques and filtering material methods. However, the above-mentioned methods have problems such as poor PER and low measurement accuracy. To solve such problems, in this study, a 1024-channel spectrometry system using a Si-PIN photodetector was developed and full-spectrum measurement in the reference radiation fields was conducted for radiation protection. The measurement results using the few-channel spectroscopy dose method showed that the PER could be controlled within ± 14% and ± 2% under the conditions of two and three energy intervals, respectively, with different channel numbers. The PER measured at 0° angle of radiation incidence meets the IEC 61526:2010 - 29% to +67% requirements of. Meanwhile, the channel number and counts-to-dose conversion factors formed in the experiment can be integrated into an EPD.
关键词： Si-PIN photodetector,Personal dose equivalent,Photon energy response,Electronic personal dosimeter,Few-channel spectroscopy dose method
更新于2025-09-23 15:19:57
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Controllable photon energy deposition efficiency in laser processing of fused silica by temporally shaped femtosecond pulse: Experimental and theoretical study
摘要： Photon energy deposition plays a crucial role in femtosecond laser irradiation followed by chemical etching processing, which is an emerging technique for the better control of micro/nano structures on fused silica. In this study, we have experimentally and theoretically studied the controllable photon energy deposition in laser irradiation of fused silica by temporally shaped femtosecond laser pulse trains. The experimental result shows that the photon energy deposition efficiency could be either reduced or enhanced by adjusting the total fluence of shaped pulse trains. Furthermore, the sub-pulse interval and intensity ratio of temporally shaped pulse trains were revealed to play a critical role in photon energy deposition. The corresponding experimental observations are qualitatively explained by a plasma model that considers the free electron generation processes and corresponding feedback on the photon energy deposition.
关键词： Photon energy deposition,Femtosecond laser,Temporally shaped pulse,Chemical etching,Fused silica
更新于2025-09-23 15:19:57
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Delocalization boosts charge separation in organic solar cells
摘要： Organic solar cells (OSCs) utilizing π-conjugated polymers have attracted widespread interest over the past three decades because of their potential advantages, including low weight, thin film flexibility, and low-cost manufacturing. However, their power conversion efficiency (PCE) has been far below that of inorganic analogs. Geminate recombination of charge transfer excitons is a major loss process in OSCs. This paper reviews our recent progress in using transient absorption spectroscopy to understand geminate recombination in bulk heterojunction OSCs, including the impact of polymer crystallinity on charge generation and dissociation mechanisms in nonfullerene acceptor-based OSCs. The first example of a high PCE with a small photon energy loss is also presented. The importance of delocalization of the charge wave function to suppress geminate recombination is highlighted by this focus review.
关键词： Polymer crystallinity,Power conversion efficiency,Organic solar cells,Transient absorption spectroscopy,Dissociation mechanisms,Photon energy loss,π-conjugated polymers,Charge generation,Nonfullerene acceptor,Geminate recombination
更新于2025-09-23 15:19:57
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Optical Fiber Communications (Principles and Applications) || Introduction
摘要： Introduction to optical fiber communications, covering historical development, electromagnetic spectrum, optical power basics, need of optical fiber communications, light wave system components, optical fibers as a communication channel, advantages and disadvantages of optical fiber cables, and applications.
关键词： optical fiber,electromagnetic spectrum,photon energy,light wave systems,communication
更新于2025-09-12 10:27:22
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Photovoltaic Effect Related to Methylammonium Cation Orientation and Carrier Transport Properties in High-Performance Perovskite Solar Cells
摘要： Solar cells based on organic-inorganic hybrid halide perovskites (OIHHP) have been widely studied due to their increasing power conversion efficiency (PCE). Extensive research has been conducted in electrical, optical properties and device fabrication. However, in terms of material science, the photovoltaic effects of OIHHP are still not well understood. Here, we theoretically investigate the photovoltaic phenomena of MAPbI3 (MA=CH3NH3+) under standard AM 1.5G sunlight illumination, considering the MA cation orientation, light incident angle, polarization and photon energy, using Keldysh non-equilibrium Green’s function formalism combined with density functional theory calculations. It is found that the short-circuit current density Jsc has a maximum value of 383.149 A/m2 when the MA orientation is parallel to the transport direction, whereas it is negligible when the MA orientation is orthogonal to the transport direction. In addition, full consideration is also given to the direction of incidence of sunlight and its polarization state. Nevertheless, of all factors considered, MA orientation plays the decisive role, for Jsc still has a respectable value of 364.112 A/m2 even for a 90-degree sunlight incident angle relative to the transport direction, so long as the MAs are aligned in the transport direction. The increase in the photocurrent is attributed to an increase in the transmission coefficient of low-energy holes, as well as improvement of the velocities and mobilities of electrons and holes in MAPbI3-based device with [001] MA orientation. The results suggest that the design of high-performance OIHHP-based solar cells and photoelectronic devices should carefully consider the crystal orientation and MA cation orientation relative to the transport direction as they directly affect carriers transport properties.
关键词： photon energy,polarization angle,cation orientation,transport properties,photocurrent,incident angle
更新于2025-09-12 10:27:22
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Spherical photon orbits in the field of Kerr naked singularities
摘要： For the Kerr naked singularity (KNS) space-times, we study properties of spherical photon orbits (SPOs) con?ned to constant Boyer-Lindquist radius r . Some new features of the SPOs are found, having no counterparts in the Kerr black hole (KBH) spacetimes, especially stable orbits that could be pure prograde/retrograde, or with turning point in the azimuthal direction. At r > 1 (r < 1) the covariant photon energy E > 0 (E < 0), at r = 1 there is E = 0. All unstable orbits must have E > 0. It is shown that the polar SPOs can exist only in the spacetimes with dimensionless spin a < 1.7996. Existence of closed SPOs with vanishing total change of the azimuth is demonstrated. Classi?cation of the KNS and KBH spacetimes in dependence on their dimensionless spin a is proposed, considering the properties of the SPOs. For selected types of the KNS spacetimes, typical SPOs are constructed, including the closed paths. It is shown that the stable SPOs intersect the equatorial plane in a region of stable circular orbits of test particles, depending on the spin a. Relevance of this intersection for the Keplerian accretion discs is outlined and observational effects are estimated.
关键词： Keplerian accretion discs,Kerr black hole,dimensionless spin,stable orbits,covariant photon energy,observational effects,closed SPOs,spherical photon orbits,azimuthal direction,Kerr naked singularity
更新于2025-09-11 14:15:04
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Murine <i>vs</i> human tissue compositions: implications of using human tissue compositions for photon energy absorption in mice
摘要： To investigate the implications of using human tissue compositions for dose calculations in mice for kilovoltage photon beams. Dual energy CT (DECT) images of 9 female mice were used to extract the effective atomic number Zeff and the relative electron density ρe for each voxel in the images. To investigate the influence of the tissue compositions on the absorbed radiation dose for a typical kilovoltage photon beam, mass energy-absorption coefficients μen/ρ were calculated for 10 different tissues in each mouse. Differences between human and murine tissue compositions can lead to errors around 7.5 % for soft tissues and 20.1 % for bone tissues in μen/ρ values for kilovoltage photon beams. When considering the spread within tissues, these errors can increase up to 17.5 % for soft tissues and 53.9 % for bone tissues within only a single standard deviation away from the mean tissue value. This study illustrates the need for murine reference tissue data. However, assigning only a single mean reference value to an entire tissue can still lead to large errors in dose calculations given the large spread within tissues of μen/ρ values found in this study. Therefore, new methods such as DECT and spectral CT imaging need to be explored, which can be important next steps in improving tissue assignment for dose calculations in small animal radiotherapy.
关键词： DECT,dose calculations,photon energy absorption,kilovoltage photon beams,spectral CT imaging,murine vs human tissue compositions
更新于2025-09-11 14:15:04
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Advances in the measurements of the mass attenuation coefficients
摘要： The knowledge of atomic fundamental parameters, such as mass attenuation coefficients or fluorescence yields with low uncertainties, is of decisive importance in elemental quantification involving X‐ray fluorescence analysis techniques. Several databases providing the mass attenuation coefficients are accessible and frequently used within a large community of users. These compilations are most often in good agreement for photon energies in the hard X‐ray ranges. However, they significantly differ for low photon energies and around the absorption edges of the elements. Mass attenuation coefficients of several elements were determined experimentally in the photon energy range from 100 eV to 35 keV by using monochromatized radiation at the SOLEIL synchrotron (France). The application of high‐accuracy experimental techniques resulted in low uncertainty mass attenuation coefficients. The results are compared with tabulated data.
关键词： photon energy,X‐ray fluorescence analysis,mass attenuation coefficients,SOLEIL synchrotron
更新于2025-09-04 15:30:14