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Interaction between Bi Dopants and Intrinsic Defects in LiNbO <sub/>3</sub> from Local and Hybrid Density Functional Theory Calculations
摘要： The interactions between Bi dopants including Bi-substituting Li (BiLi) and Bi-substituting Nb (BiNb) and the intrinsic antisite defects (NbLi) and Li vacancies (VLi) in LiNbO3 are investigated using local and hybrid density functional theories. Three charge-compensated defect clusters, BiLi4+ + NbLi4+ + 8VLi-, BiLi4+ + 4VLi-, and BiLi0 + 4VLi- + BiNb4+, are modeled in this work to investigate the effects of the Bi concentration. The most stable cluster configurations, the Bi-doping stability in the clusters, and the electronic state interaction between Bi and intrinsic defects have been studied in detail. It is found that BiLi4+ has a stronger electron-capturing ability than NbLi4+ in Bi-doped congruent LiNbO3. The BiLi-doping-induced local lattice distortion and the electron-trapping behavior remain unchanged with increasing Bi-doping concentration. However, the position of the Bi defect states in the band gap is found to be shifted in congruent LiNbO3. This is mainly attributed to the large lattice relaxation induced by the large number of Li vacancies instead of the ionic level redistribution caused by the direct interaction between Bi and intrinsic defects.
关键词： LiNbO3,Bi dopants,lattice distortion,defect clusters,intrinsic defects,density functional theory,electron trapping
更新于2025-09-19 17:15:36
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The role of moisture in the preparation for efficient planar perovskite solar cells
摘要： Perovskite solar cells (PSC) have achieved a certificated efficiency of 25.2% within the past few years. Among effective methods, one of the most effective approaches obtaining highly-efficient PSCs is the moisture-assisted annealing process. However, the role of moisture in the preparation of high-performance PSCs is under intense debate. Herein the critical effect of moisture in the preparation of efficient Formamidinium (FA) based PSCs with improved-quality perovskite films is systematically investigated based on diverse characterizations. Consequently, the optimal amount of moisture is determined at 50% relative humidity (RH) which produces perovskite films of higher quality with larger and uniform grains size in comparison to the control films prepared in the glovebox. Specifically, prolonged lifetime, reduced defects densities and higher light harvesting capability of perovskite films annealed in 50RH% are confirmed by the photoluminescence (PL), the time-resolved PL (TRPL), the space charge limited current (SCLC) and the confocal laser scanning microscopy (CLSM), respectively. These results indicate the environments with a controlled level of moisture is preferable for achieving high-quality perovskite films and the compatibility of fabricating highly-efficient PSCs under ambient conditions with controlled moisture for future industrial mass production.
关键词： defects density,two-step deposition,Planar perovskite solar cells,moisture,space-charge-limited current
更新于2025-09-16 10:30:52
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Structural stability and energy levels of carbon-related defects in amorphous SiO <sub/>2</sub> and its interface with SiC
摘要： We report the density-functional calculations that systematically clarify the stable forms of carbon-related defects and their energy levels in amorphous SiO2 using the melt-quench technique in molecular dynamics. Considering the position dependence of the O chemical potential near and far from the SiC/SiO2 interface, we determine the most abundant forms of carbon-related defects: Far from the interface, the CO2 or CO in the internal space in SiO2 is abundant and they are electronically inactive; near the interface, the carbon clustering is likely and a particular mono-carbon defect and a di-carbon defect induce energy levels near the SiC conduction-band bottom, thus being candidates for the carrier traps.
关键词： melt-quench technique,amorphous SiO2,carbon-related defects,density-functional calculations,SiC/SiO2 interface
更新于2025-09-10 09:29:36
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Bandgap opening in graphene using alkali ions by first principles
摘要： Recently, bandgap opening at the Dirac point in graphene, formed on SiC(0001) surfaces, has been reported in different experiments, by deposition of positively charged alkali ions. This is clearly of great relevance for the countless practical applications of graphene in nano-electronic devices. By first principles calculations, based on the Density Functional Theory, the electronic band structure and the energetic properties are obtained for Na+, K+, and Cs+ ions interacting with graphene on SiC. We show that simple adsorption of alkali ions on intact graphene cannot give rise to a significant energy gap. An appreciable bandgap opening, similar to that observed in actual experiments, occurs instead due to the formation of Stone-Wales defects and substitutional defects (where positively charged alkali ions replace carbon atoms) that lead to a significant breaking of the charge symmetry among the carbon atoms of pristine graphene.
关键词： bandgap opening,graphene,alkali ions,Stone-Wales defects,substitutional defects,Density Functional Theory,first principles
更新于2025-09-09 09:28:46