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Interfacial charge dynamics of cross-linked polyethylene/ethylene-propylene-diene dual dielectric polymer as revealed by energy band structure
摘要： The discontinuous charge relaxation time related to the electrical conductivity and permittivity, i.e., traditional Maxwell-Wagner relaxation, is the prevailing explanation for the interfacial charge behavior in multi-layered dielectrics. However, the unipolar/bipolar charge dynamics and the corresponding mechanisms from a microscopic viewpoint remain unclear. This work focuses on the dynamics of the interfacial charges in cross-linked polyethylene (XLPE)/ethylene-propylene-diene (EPDM) dual layers to reveal the interfacial charge mechanisms using the energy band structure. The interfacial charge accumulation behavior of the XLPE/EPDM dual- layered structures is clearly observed under electrical stress. Either unipolar or bipolar charges occur at the interface, accompanied by charge injection, and trapping then occurs. The positive charges prefer to accumulate and migrate on the XLPE side. The homo-charges at the interface always remain on the EPDM side. The number of negative charges is higher than the number of positive charges at the interface. The bipolar interfacial charges are ascribed to the charge transfer process that occurs at the interface because of the energy level alignment that is revealed by the electronic energy structures of XLPE and EPDM. The trapping sites, along with the charge injection and transport, contribute to the interfacial charge behavior.
关键词： energy level,interface,trapping site,space charge,energy band structure
更新于2025-09-12 10:27:22
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Highly efficient perovskite solar cells based on a Zn2SnO4 compact layer
摘要： In the present work, a new reflux condensation route has been developed for synthesizing Zn2SnO4 film, which was first used as a compact layer in a perovskite solar cell (PSC), and achieved an efficiency of 20.1%. The high efficiency of PSC could be contributed to the following: i) As a compact layer in a PSC, Zn2SnO4 exhibits high electron mobility and has an appropriate energy band structure, resulting in the efficient extraction of carriers and transport of electrons; ii) the surface of the FTO substrate is completely covered by a Zn2SnO4 compact layer, and the direct contact between a perovskite layer and FTO is prevented, leading to significantly efficiently suppression of charge recombination. Consequently, the cell consisting of a Zn2SnO4 compact layer exhibits excellent photovoltaic performance.
关键词： Zn2SnO4,photovoltaic property,compact layer,perovskite solar cells,charge recombination,energy band structure
更新于2025-09-11 14:15:04
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Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 phosphors: electronic, crystal structures and photoluminescence properties
摘要： The union of chemical compositions substitution and spectral controlling is of importance for the discovery of new materials or the implementation of properties optimization. In this work, we employed an effective strategy to regulate crystal structures by chemical unit co-substitution. We applied this strategy to Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 (0 ≤ x ≤ 1) solid solution phosphor, which was successfully synthesized by high temperature solid state reaction. The crystal structure remained the same group, P-421m, with controlling chemical compositions. The excitation peaks shifted between 263 and 270 nm and emission peaks shifted between 612 and 614 nm with a decreasing Stocks shift in overall tendency. The shift trend was clarified by Crystal Field Theory. The energy band structure and density of states of Sr2Al2SiO7 and Sr2MgSi2O7 were calculated by Density Functional Theory using the generalized gradient approximation. The band gap was also analyzed by diffuse reflectance spectrum as a contrast. The morphology was characterized by field emission scanning electron microscopy. Furthermore, the photoluminescence color of phosphors could be tuned from yellow to orange.
关键词： crystal structure,chemical unit co-substitution,phosphors,photoluminescence,energy band structure
更新于2025-09-09 09:28:46
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First-principles investigation of the electronic band structures and optical properties of quaternary <i>A</i> Ba <i>MQ</i> <sub/>4</sub> ( <i>A</i> = Rb, Cs; <i>M</i> = P, V; and <i>Q</i> = S) metal chalcogenides
摘要： In this paper, we study the optoelectronic properties of quaternary metal chalcogenide semiconductor ABaM Q4 (A = Rb, Cs; M = P, V; and Q = S) compounds using state-of-the-art density functional theory (DFT) with TB-mBJ approximation for the treatment of exchange-correlation energy. In particular, the electronic and optical properties of the relaxed geometries of these compounds are investigated. Our first-principles ab-initio calculations show that the CsBaPS4 and RbBaPS4 compounds have direct bandgaps whereas the CsBaVS4 compound exhibits indirect bandgap nature. Importantly, the theoretically calculated values of the bandgaps of the compounds are consistent with experiment. Furthermore, our analysis of the electronic charge densities of these compounds indicates that the above quaternary chalcogenides have mixed covalent and ionic bonding characters. The effective masses of these compounds are also calculated which provide very useful information about the band structure and transport characteristics of the investigated compounds. Similarly, high absorptivity in the visible and ultraviolet regions of the electromagnetic spectrum possibly predicts and indicates the importance of these materials for potential optoelectronic applications in this range.
关键词： energy band structure,electronic charge densities,optical conductivity,Chalcogenides,refractive index,dielectric constants,optical reflectivity
更新于2025-09-09 09:28:46