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- 摘要
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- 实验方案
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Epitaxial growth and determination of the band alignment for NixMg1-xO/MgO interface by laser molecular beam epitaxy
摘要： By laser molecular beam epitaxy, single crystalline NixMg1-xO films have been successfully synthesized on MgO(100) surface. The in situ reflection high-energy electron diffraction patterns show that the induced O2 background gas with at least 1.0 × 10?3 Pa is necessary to the epitaxial growth of NixMg1-xO films. The X-ray diffraction patterns reveal the single-phase growth along (200) direction. The energy band alignment at the interface is investigated by employing in situ X-ray photoelectron spectroscopy. The valence band offsets are determined to be from 1.47 eV to 1.50 eV with the decrease of Ni content (0.39 / 0.35). Furthermore, the work function is evaluated by using in situ ultraviolet photoemission spectroscopy, indicating the values from 4.33 eV to 4.64 eV. This study provides a promising guidance for the solar-blind device design and fabrication.
关键词： Work function,X-ray photoelectron spectroscopy,Band alignment,Ultraviolet photoemission spectroscopy,Laser molecular beam epitaxy
更新于2025-09-19 17:13:59
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Internal Atomic-Scale Structure Determination and Band Alignment of IIa??VI Quantum Dot Heterostructures
摘要： This work shows that ZnTe/CdSe core/shell quantum dots synthesized by a standard literature procedure in actuality have an alloyed CdxZn1?xTe core. We employ X-ray absorption spectroscopy (XAS) at all four K-shell ionization edges (Zn, Te, Cd, and Se) and perform global ?tting analysis to extract the ?rst-shell bond distances. We combine our XAS results with transmission electron microscopy (TEM) sizing and elemental analyses, which allows us to propose models of the internal particle structure. Our multimodal characterization approach con?rms (1) the presence of Cd?Te bonds, (2) cation alloying in the particle core (and the absence of anion alloying), and (3) a patchy pure-phase CdSe shell. We synthesize particles of di?erent shell thicknesses and performed synthetic control studies that allowed us to discard a ZnTe/CdTe/CdSe core/shell/shell structure and con?rm the alloyed core/shell structure. Our structural analysis is extended with electronic band structure calculations and UV/vis absorption spectroscopy, demonstrating that the alloyed CdxZn1?xTe/CdSe core/shell quantum dots exhibit a direct band gap, di?erent from the predicted type II band alignment of the intended ZnTe/CdSe core/shell quantum dots. This study highlights the challenges with synthesizing II?VI quantum dot heterostructures and the power of XAS for understanding the internal structure of heterogeneous nanoparticles.
关键词： X-ray absorption spectroscopy,alloyed core,core/shell,band alignment,quantum dots
更新于2025-09-19 17:13:59
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Type-II/type-II band alignment to boost spatial charge separation: A case study of g-C3N4 quantum dot/a-TiO2/r-TiO2 for highly efficient photocatalytic hydrogen and oxygen evolution
摘要： Efficient spatial charge separation and transfer that are critical factors for solar energy conversion primarily depend on the energetic alignment of the band edges at interfaces in heterojunctions. Herein, we first report that constructing 0D/0D type-II(T-II)/T-II heterojunction is an effective strategy to ingeniously achieve long-range charge separation by taking a ternary heterojunction of TiO2 and graphitic carbon nitride (g-C3N4) as a proof-of-concept. Incorporating g-C3N4 quantum dots (QCN), as the third component, into the commercial P25 composed of anatase (a-TiO2) and rutile (r-TiO2) can be realized via simply mixing the commercially Degussa P25 and QCN solution followed by heat treatment. The strong coupling and matching band structures among a-TiO2, r-TiO2 and QCN result in the construction of novel T-II/T-II heterojunctions, which would promote the spatial separation and transfer of photogenerated electrons and holes. Moreover, QCN plays a key role in reinforcing light absorption. Specially, the unique 0D/0D architecture possesses the advantages of abundant active sites for photocatalytic reaction. As a result, the optimized QCN/a-TiO2/r-TiO2 heterojunctions exhibit enhanced photocatalytic H2 and O2 evolution, especially the hydrogen evolution rate (49.3 μmol h?1) is 11.7 times that of bare P25 under visible light irradiation, and sufficiently catalytic stability as evidenced by the recycling experiments. The remarkable enhanced photocatalytic activity can be attributed to the synergistic effects of the energy level alignment at interfaces, the dimensionality and component of the heterojunctions. This work provides a stepping stone towards the design of novel heterojunctions for photocatalytic water splitting.
关键词： type-II/type-II band alignment,0D/0D heterojunction,photocatalytic water splitting,g-C3N4 quantum dots,TiO2
更新于2025-09-19 17:13:59
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One-step synthesis of strongly confined, defect-free and hydroxy-terminated ZnO quantum dots
摘要： This paper reports the production of strongly con?ned ligand-free, defect-free, hydroxy-terminated ZnO quantum dots with a mean diameter of 1.9 nm, by radio frequency atmospheric pressure microplasma. Systematic characterization is performed to understand the surface chemistry of ZnO quantum dots. Photoluminescence studies show strong con?nement effect on emission with only ultraviolet (UV) emission without any defect-related visible emission. Emission is again tested after eighteen months and con?rms the QDs long-term emission stability. The mechanism responsible for this UV emission is also discussed and originates from OH-related surface terminations.
关键词： band alignment,quantum con?nement,defect-free,photoluminescence,hydroxy-terminated ZnO quantum dots
更新于2025-09-19 17:13:59
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Determination of band alignment at the CdTe/SnTe heterojunction interface for CdTe thin-film solar cells
摘要： The Ohmic back contact for CdTe is a key issue to realize high-efficiency CdTe thin film solar cells because of the high work function of CdTe. CdTe/SnTe heterojunctions (HJs) have been implemented to address this issue which shows promising potential, but the band alignment at the HJs is unknown. The valence band offsets in MBE-grown cadmium telluride (CdTe)/tin telluride (SnTe) (111) heterostructures were measured with X-ray photoelectron spectroscopy (XPS). The XPS results show that the heterostructure has an ideal type-I band structure for CdTe solar cells applications, with a valence band offset of ?1.33 ± 0.18 eV and a conduction band offset of 0.09 ± 0.18 eV, which expedites hole transport from the CdTe absorber to the hole electrode and improves the Ohmic contact for CdTe. Experimental determination of the band structure of CdTe/SnTe HJs can help improve the photovoltaic performance of CdTe thin film solar cells and facilitate the design and fabrication of CdTe/SnTe related devices. Furthermore, we inserted a SnTe back contact buffer layer into the CdTe thin film solar cells, and it was compared with the cell structure without the SnTe buffer layer. The feasibility of using SnTe as a solar cell back contact is confirmed.
关键词： solar cells,CdTe,heterojunction,band alignment,XPS,SnTe
更新于2025-09-19 17:13:59
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Sandwich-like electron transporting layer to achieve highly efficient perovskite solar cells
摘要： Passivating the carrier recombination at the heterojunction interface and improving the efficiency of charge separation are effective means to boost the performance of perovskite solar cells (PSCs). The interface modification between the anode and the electron transporting layer (ETL) or constructing bilayer structural ETLs has been proved to be the effective way to achieve high-efficient charge extraction and collection. Combining the advantages of both techniques might further achieve lower energy loss and higher efficiency in PSCs. Herein, we design a sandwich-like SnO2-CQDs-SnO2 (S–C–S) ETLs, i.e. an ultrathin band-gap tunable carbon quantum dots (CQDs) layer is inserted between ultrathin SnO2 bottom layer and SnO2 top layer. The bottom ultrathin SnO2 layer passivates the defects of SnO2:F (FTO) and reduces the carrier recombination at the FTO/ETLs interface. The CQDs layer enhances the optical transmission of ETLs, accelerates carrier transport process and improves the hole-blocking ability. Such S–C–S ETLs greatly enhance the power conversion efficiency (PCE) of PSCs and eliminate hysteresis to the maximum extent. This work provides a new concept for designing novel electronic transmission materials for solar cells, and lays the foundation for further achieving higher PCE in PSCs.
关键词： Power conversion efficiency,Sandwich-like electron transporting layer,Band alignment,Perovskite solar cell,Interface modification
更新于2025-09-19 17:13:59
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Highly efficient Zn <sub/>2</sub> SnO <sub/>4</sub> perovskite solar cells through band alignment engineering
摘要： An active absorption layer with a narrow band gap has been achieved through adjusting the halide ratio in a halide perovskite, and it had better energy alignment with the Zn2SnO4 electron transport layer. An e?ciency of 19.37% can be obtained, and this has also been improved to 20.26% through the incorporation of cesium, giving a new triple cation perovskite.
关键词： band alignment engineering,perovskite solar cells,efficiency,Zn2SnO4
更新于2025-09-16 10:30:52
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On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment
摘要： Earth-abundant and environmentally-friendly Cu2–II–IV–VI4 (II = Sr, Ba; IV = Ge, Sn; VI = S,Se) are considered materials for the absorber layers in thin film solar cells. Attempts to understand and improve optoelectronic properties of these newly emerged absorbers resulted in an efficiency of 5.2% in less than two years. However, the energy band alignment at the buffer/absorber interface has not been studied yet; an information which is of crucial importance for designing high performance devices. Therefore, current study focuses on the band offsets between these materials and the CdS buffer. Using first-principles calculations, band discontinuities are calculated at the buffer/absorber interface. The results yield a type-II band alignment between all Cu2–II–IV–VI4 absorbers and CdS, hence a negative DEc. Adoption of a negative DEc (cliff-like conduction band offset) at the buffer/absorber interface, however, gives rise to low open circuit voltage and high interface-related recombinations. Therefore, it is necessary to search for an alternative buffer material that forms a type-I band alignment with these absorbers, where the conduction band minimum and the valence band maximum are both localized on the absorber side.
关键词： buffer/absorber interface,earth-abundant chalcogenides,band alignment,first-principles calculations
更新于2025-09-16 10:30:52
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Band offset modulation in Si-EuO heterostructures via controlled interface formation
摘要： Combining first-principles calculations and experiment, we investigate the atomic and electronic structure of the Si/EuO interface. We consider the thermodynamic stability of interface structures with different levels of oxidation to identify the most probable configuration. By comparing the calculated band alignment and core-level shifts with measured values, we validate the theoretically constructed interface model. We find that the band offset can be tuned by altering the relative energy positions of the Si and EuO conduction bands via interface oxidation, which can be used to tune this materials system for specific applications in spintronics.
关键词： XPS,band alignment,first-principles calculations,Si/EuO interface,spintronics
更新于2025-09-12 10:27:22
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Broad tunability of emission wavelength by strain coupled InAs/GaAs <sub/>1???x</sub> Sb <sub/>x</sub> quantum dot heterostructures
摘要： Tuning of the photoluminescence emission over a wider range of optical telecommunication wavelength (1.38 μm–1.68 μm) has been achieved by employing a GaAs1 ? xSbx capping layer to the strain coupled bilayer InAs quantum dot (QD) heterostructures. It is shown that the modulation of strain between the two dot layers through variation in Sb-content and thickness of the capping layer strongly influence the dot size. The band alignment transformation from type-I to type-II is observed for high Sb-content in the capping layers. In addition, the carrier lifetime is improved by a factor of three in the QD heterostructures having type-II band alignment. This, we believe, is of importance for optoelectronic device applications.
关键词： GaAs1 ? xSbx capping layer,carrier lifetime,optoelectronic device applications,photoluminescence emission,strain coupled bilayer InAs quantum dot,type-I to type-II band alignment,optical telecommunication wavelength
更新于2025-09-12 10:27:22