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Surface doping of ZnO nanowires with Bi: Density-functional supercell calculations of defect energetics
摘要： Defect calculations using the density and hybrid functionals in combination with the supercell approach are employed to characterize the electrical properties of a number of ZnO nanowires of various thicknesses doped with Bi atoms occupying surface sites. The variation of the differences between the total energies of charged and neutral supercells with the supercell size is studied, which led the authors to devise an extrapolation procedure to obtain reliable defect energetics in the dilute defect limit. The calculated defect formation energies indicate that although the substitution of Bi into Zn or O sites can take place spontaneously under suitable thermodynamic conditions, the substitution into Zn sites is generally more likely. The defect (charge-state) transition energies are computed and parameterized as a function of the nanowire thickness. It is revealed that the substitution of Bi into O (Zn) sites on the surface of ZnO nanowires yields deep acceptor (shallow donor) levels (except for extremely thin nanowires). It is therefore concluded that the incorporation of Bi into the surface of ZnO nanowires results in n-type doping.
关键词： ZnO nanowires,defect energetics,n-type doping,bismuth doping,supercell calculations,density functional theory
更新于2025-09-23 15:23:52
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Energetics and Energy Loss in 2D Ruddlesdena??Popper Perovskite Solar Cells
摘要： 2D Ruddlesden–Popper perovskites (RPPs) are emerging as potential challengers to their 3D counterpart due to superior stability and competitive efficiency. However, the fundamental questions on energetics of the 2D RPPs are not well understood. Here, the energetics at (PEA)2(MA)n?1PbnI3n+1/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) interfaces with varying n values of 1, 3, 5, 40, and ∞ are systematically investigated. It is found that n–n junctions form at the 2D RPP interfaces (n = 3, 5, and 40), instead of p–n junctions in the pure 2D and 3D scenarios (n = 1 and ∞). The potential gradient across phenethylammonium iodide ligands that significantly decreases surface work function, promotes separation of the photogenerated charge carriers with electron transferring from perovskite crystal to ligand at the interface, reducing charge recombination, which contributes to the smallest energy loss and the highest open-circuit voltage (Voc) in the perovskite solar cells (PSCs) based on the 2D RPP (n = 5)/PCBM. The mechanism is further verified by inserting a thin 2D RPP capping layer between pure 3D perovskite and PCBM in PSCs, causing the Voc to evidently increase by 94 mV. Capacitance–voltage measurements with Mott–Schottky analysis demonstrate that such Voc improvement is attributed to the enhanced potential at the interface.
关键词： energy loss,2D Ruddlesden–Popper perovskites,open-circuit voltage,perovskite solar cells,energetics
更新于2025-09-23 15:21:01
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Surface Ligands for Methylammonium Lead Iodide Films: Surface Coverage, Energetics, and Photovoltaic Performance
摘要： Surface ligand treatment provides a promising approach to passivate defect states, improve material and device stability, manipulate interfacial energetics, and increase the performance of perovskite solar cells (PSCs). To facilitate targeted selection and design of surface ligands for PSCs, it is necessary to establish relationships between ligand structure and perovskite surface properties. Herein, surface ligands with different binding groups are investigated to determine their extent of surface coverage, whether they form a surface monolayer or penetrate the perovskite, how they influence material energetics and photoluminescence, and how this combination of factors affects PSC performance. Ultraviolet and inverse photoelectron spectroscopy measurements show that surface ligands can significantly shift the ionization energy and electron affinity. These changes in surface energetics substantially impact PSC performance, with the performance decreasing for ligands that create less favorable energy landscapes for electron transfer from MAPbI3 to the electron transport layer, C60.
关键词： defect passivation,perovskite solar cells,interfacial energetics,surface ligands,photovoltaic performance
更新于2025-09-19 17:13:59
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The experimental investigation of the <i>hohlraum</i> energetics of two-entrance holes spherical <i>hohlraum</i> at the 100 kJ level laser facility
摘要： The two-laser entrance hole (LEH) spherical hohlraum energetic experiments with all 48 laser beams and two laser pulse shapes at the 100 kJ level laser facility were investigated. In this work, the time-resolved radiation temperature measured by multi-angle x-ray diodes agreed well with LARED simulations, and the peak radiation temperature was up to 260 eV with the laser power of 45 TW. Meanwhile, the backscattered laser energy fraction was less than 5% in the majority of shots, which proposed a low level of laser–plasma interaction (LPI) effect in the spherical hohlraum. However, in the shaped pulse shots with capsules, the stimulated Raman scattering (SRS) of smaller incident angle lasers was signi?cantly increased to 15%. The measured SRS spectrum and LARED simulations showed that the increase in the LPI effects caused by the ablated CH plasma was around 0.1Nc (Nc is the critical density). In summary, according to the experimental results, the x-ray conversion ef?ciency of the vacuum spherical hohlraum was 85%–88% in 3 ns square pulses and 89%–93% in 3.6 ns shaped pulses. It was closer to that of the two-LEH cylindrical hohlraum at the Shen-Guang and NIF facilities.
关键词： LARED simulations,laser-plasma interaction,x-ray conversion efficiency,hohlraum energetics,spherical hohlraum
更新于2025-09-19 17:13:59
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Influence of Surface Ligands on Energetics at FASnI <sub/>3</sub> /C <sub/>60</sub> Interfaces and Their Impact on Photovoltaic Performance
摘要： Interfacial chemistry and energetics significantly impact the performance of photovoltaic devices. In the case of Pb-containing organic metal halide perovskites, photoelectron spectroscopy has been used to determine the energetic alignment of frontier electronic energy levels at various interfaces present in the photovoltaic device. For the Sn-containing analogues, which are less toxic, no such measurements have been made. Through a combination of inverse, and X-ray photoelectron spectroscopy ultraviolet, (UPS, IPES, and XPS, respectively) measurements taken at varying thickness increments during stepwise deposition of C60 on FASnI3, we present the first direct measurements of the frontier electronic energy levels across the FASnI3/C60 interface. The results show band bending in both materials and transport gap widening in FASnI3 at the interface with C60. The XPS results show that iodide diffuses into C60 and results in n-doping of C60. This iodide diffusion out of FASnI3 impacts the valence and conduction band energies of FASnI3 more than the core levels, with the core level shifts displaying a different trend than the valence and conduction bands. Surface treatment of FASnI3 with carboxylic acids and bulky ammonium substituted surface ligands results in slight alterations in the interfacial energetics, and all surface ligands result in similar or improved PV performance relative to the untreated devices. The greatest PV stability results from treatment with a fluorinated carboxylic acid derivative; however, iodide diffusion is still observed to occur with this surface ligand.
关键词： perovskite solar cell,formamidinium tin iodide,interfacial energetics,inverse photoelectron spectroscopy,surface modification,photoelectron spectroscopy,ion diffusion
更新于2025-09-12 10:27:22
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Deterministic switching of the growth direction of self-catalyzed GaAs nanowires
摘要： Typical vapor-liquid-solid growth of nanowires is restricted to vertical one-dimensional geometry, while there is a broad interest for more complex structures in the context of electronics and photonics applications. Controllable switching of the nanowire growth direction opens up new horizons in the bottom-up engineering of self-assembled nanostructures, for example, to fabricate interconnected nanowires used for quantum transport measurements. In this work, we demonstrate a robust and highly controllable method for deterministic switching of the growth direction of self-catalyzed GaAs nanowires. The method is based on the modification of the droplet-nanowire interface in the annealing stage without any fluxes and subsequent growth in the horizontal direction by a twin-mediated mechanism with indications of a novel type of interface oscillations. A 100% yield of switching the nanowire growth direction from vertical to horizontal is achieved by systematically optimizing the growth parameters. A kinetic model describing the competition of different interface structures is introduced to explain the switching mechanism and the related nanowire geometries. The model also predicts that growth of similar structures is possible for all vapor-liquid-solid nanowires with commonly observed truncated facets at the growth interface.
关键词： Growth direction,Surface energetics,Self-catalyzed GaAs nanowires,Crystal facets
更新于2025-09-04 15:30:14