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Ambipolar and Robust WSe <sub/>2</sub> Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides
摘要： Transition metal oxides (TMOs) with high work function (WF) show promising properties as unipolar p-type contacts for transition metal dichalcogenides. Here, ambipolar field-effect transistors (FETs) enabled by bilayer WSe2 with self-assembled TMOs (WO2.57) as contacts are reported. Systematic material characterizations demonstrate the formation of WO2.57/WSe2 heterojunctions around nanoflake edges with Se atoms substituted by O atoms after air-exposure, while pristine properties of WSe2 almost sustain in inner domains. As-fabricated FETs exhibit both polarities, implying WO2.57 with lowered WF at edges can serve as both the p-type and n-type contact for inner WSe2. Noteworthy, greatly reduced contact resistance and enhanced channel current are achieved, compared to the devices without WO2.57 contacts. Linear drain–source current relationship from 77 to 300 K indicates the ohmic contact between edge WO2.57 and inner WSe2. Density functional theory calculations further reveal that the WO2.57/WSe2 heterojunction forms a barrier-less charge distribution. These nm-scale FETs possess remarkable electrical conductivity up to ≈2600 S m?1, ultra-low leakage current down to ≈10?12 A, robustness for high voltage operation, and air stability, which even outperform pristine WSe2 FETs. Theoretical calculations reveal that the high conductivity is exclusively attributed to the air-induced WO2.57 and its further carrier injection to WSe2.
关键词： field-effect transistors,self-passivation,WOx,density functional theory,WSe2
更新于2025-09-11 14:15:04
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Simultaneous Contact and Grain‐Boundary Passivation in Planar Perovskite Solar Cells Using SnO <sub/>2</sub> ‐KCl Composite Electron Transport Layer
摘要： The performance of perovskite solar cells is sensitive to detrimental defects, which are prone to accumulate at the interfaces and grain boundaries of bulk perovskite films. Defect passivation at each region will lead to reduced trap density and thus less nonradiative recombination loss. However, it is challenging to passivate defects at both the grain boundaries and the bottom charge transport layer/perovskite interface, mainly due to the solvent incompatibility and complexity in perovskite formation. Here SnO2-KCl composite electron transport layer (ETL) is utilized in planar perovskite solar cells to simultaneously passivate the defects at the ETL/perovskite interface and the grain boundaries of perovskite film. The K and Cl ions at the ETL/perovskite interface passivate the ETL/perovskite contact. Meanwhile, K ions from the ETL can diffuse through the perovskite film and passivate the grain boundaries. An enhancement of open-circuit voltage from 1.077 to 1.137 V and a corresponding power conversion efficiency increasing from 20.2% to 22.2% are achieved for the devices using SnO2-KCl composite ETL. The composite ETL strategy reported herein provides an avenue for defect passivation to further increase the efficiency of perovskite solar cells.
关键词： electron transport layer,perovskite solar cells,defect passivation
更新于2025-09-11 14:15:04
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Self-assembled Fluorinated Polymer Passivation Layer for Efficient Perovskite Thin-film Solar Cells
摘要： We report the fabrication of self-assembled surface-passivated [CH(NH2)2]0.8Cs0.2PbI3 thin films using a one-step method with a fluorinated polymer (FP) as an additive without post-treatment. The FP phase is separated and aggregated at the top surface of the perovskite layer during film formation. This FP acts as a passivation layer and improves the short-circuit current density and the fill factor consequently, the power conversion efficiency increases from 17.2% for the FP-free device to 19.1% for the 4-mg/mL-FP-added device.
关键词： Perovskite solar cells,Surface Passivation,Fluorinated Polymer
更新于2025-09-11 14:15:04
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Annealing Impact on Interface Properties of Sprayed Al2O3-Based MIS Structure for Silicon Surface Passivation
摘要： Aluminum oxide (Al2O3) films of different thicknesses were deposited on quartz and silicon (100) substrates by an ultrasonic spray method from a solution of aluminum acetylacetonate dissolved in N,N-dimethylformamide with different molar concentrations. The optical, morphological and electrical properties were investigated. Increasing the molar concentration leads to a refractive index decrease, an increase in the optical band gap from 5.26 eV to 5.52 eV and a change in the surface roughness of the films. The electrical parameters at the Al2O3/Si interface such as the flat band voltage (VFB), effective charge density (Qeff) and interface trap density (Dit) were explored as a function of the molar concentration, film thickness and heat treatment. The latter, done by two annealing processes, namely, the post deposition annealing (PDA) and post metallization annealing (PMA) on the structure, lead to remarkable interface properties. It was found that the positive flat band voltage VFB shift is correlated with the generation of negative effective charge during PMA. A decrease of the Dit distribution in the PMA samples with no significant effect in the case of PDA samples was clearly observed for different molar concentrations. Furthermore, as the Al2O3 film thickness decreases, Dit decreases in both PDA and PMA samples while the relatively high density Qeff and its negative charge polarity were obtained for thinner films. A noticeable passivation effect on the Al2O3/Si interface has been confirmed on samples that underwent the annealing process. These findings related specifically to the interface properties are promising for silicon surface passivation, in particular for solar cells applications.
关键词： Al2O3,surface passivation,ultrasonic spray,post-metallization annealing,post-deposition annealing
更新于2025-09-10 09:29:36
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Design Principles for Trap-Free CsPbX <sub/>3</sub> Nanocrystals: Enumerating and Eliminating Surface Halide Vacancies with Softer Lewis Bases
摘要： We introduce a general surface passivation mechanism for cesium lead halide perovskite materials (CsPbX3, X = Cl, Br, I) that is supported by a combined experimental and theoretical study of the nanocrystal surface chemistry. A variety of spectroscopic methods are employed together with ab initio calculations to identify surface halide vacancies as the predominant source of charge trapping. The number of surface traps per nanocrystal is quantified by 1H NMR spectroscopy, and that number is consistent with a simple trapping model in which surface halide vacancies create deleterious under-coordinated lead atoms. These halide vacancies exhibit trapping behavior that differs between CsPbCl3, CsPbBr3, and CsPbI3. Ab initio calculations suggest that introduction of anionic X-type ligands can produce trap-free band gaps by altering the energetics of lead-based defect levels. General rules for selecting effective passivating ligand pairs are introduced by considering established principles of coordination chemistry. Introducing softer, anionic, X-type Lewis bases that target under-coordinated lead atoms results in absolute quantum yields approaching unity and monoexponential luminescence decay kinetics, thereby indicating full trap passivation. This work provides a systematic framework for preparing highly luminescent CsPbX3 nanocrystals with variable compositions and dimensionalities, thereby improving fundamental understanding of these materials and informing future synthetic and post-synthetic efforts towards trap-free CsPbX3 nanocrystals.
关键词： charge trapping,nanocrystals,surface passivation,ab initio calculations,halide vacancies,CsPbX3,ligand exchange,quantum yield
更新于2025-09-10 09:29:36
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Coulomb scattering mechanism transition in 2D layered MoTe <sub/>2</sub> : effect of high- <i>κ</i> passivation and Schottky barrier height
摘要： Clean interface and low contact resistance are crucial requirements in two-dimensional (2D) materials to preserve their intrinsic carrier mobility. However, atomically thin 2D materials are sensitive to undesired Coulomb scatterers such as surface/interface adsorbates, metal-to-semiconductor Schottky barrier (SB), and ionic charges in the gate oxides, which often limits the understanding of the charge scattering mechanism in 2D electronic systems. Here, we present the effects of hafnium dioxide (HfO2) high-κ passivation and SB height on the low-frequency (LF) noise characteristics of multilayer molybdenum ditelluride (MoTe2) transistors. The passivated HfO2 passivation layer significantly suppresses the surface reaction and enhances dielectric screening effect, resulting in an excess electron n-doping, zero hysteresis, and substantial improvement in carrier mobility. After the high-κ HfO2 passivation, the obtained LF noise data appropriately demonstrates the transition of the Coulomb scattering mechanism from the SB contact to the channel, revealing the significant SB noise contribution to the 1/f noise. The substantial excess LF noise in the subthreshold regime is mainly attributed to the excess metal-to-MoTe2 SB noise and is fully eliminated at the high drain bias regime. This study provides a clear insight into the origin of electronic signal perturbation in 2D electronic systems.
关键词： Coulomb screening,low-frequency noise,Schottky barrier height,molybdenum ditelluride,high-κ passivation
更新于2025-09-10 09:29:36
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Effects of Surface Passivation on Photoluminescence Properties and Biomedical Imaging of Graphene Quantum Dots
摘要： Owing to fluorescence properties and small size, graphene quantum dots (GQDs) have been investigated for biomedical imaging. Although GQDs demonstrate some desirable properties, their poor stability and low biocompatibility have applications in various aspects. Therefore, in this study, we synthesized surface-passivated GQDs and studied their properties. GQDs were prepared using thermal exfoliation of graphite oxide, followed by nitric acid refluxing. Then GQDs were passivated with polyethylene glycol (PEG) using hydrothermal at 120 ℃ for 72 h. Both GQDs and GQDs-PEG were characterized by transmission electron microscopy, UV-Vis absorption and photoluminescence spectroscopy. Compared with GQDs, GQDs-PEG exhibit higher fluorescence intensity and fluorescent quantum yield. Also, GQDs-PEG demonstrates less cytotoxicity than GQDs in terms of cell survival rate in MTT assay. Our findings demonstrate that both fluorescence characteristics and biocompatibility of GQDs can be improved by PEG surface passivation, and GQDs-PEG is desirable for biomedical imaging.
关键词： surface passivation,biomedical imaging,graphene quantum dots,photoluminescence,polyethylene glycol
更新于2025-09-10 09:29:36
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Effect of surface passivation process for AlGaN/GaN HEMT heterostructures using phenol functionalized-porphyrin based organic molecules
摘要： In this work, we investigate an unexplored possibility of passivating the charged surface states on AlGaN/GaN high electron mobility transistor (HEMT) heterostructures by using organic molecules. This has further led to remarkable enhancement in the electrical properties of rectifying metal-semiconductor contacts on AlGaN/GaN. Phenol functionalized Zinc metallated-Tetra Phenyl Porphyrin (Zn-TPPOH) organic molecules were adsorbed on AlGaN/GaN via the solution phase to form a molecular layer (MoL). The presence of the MoL was confirmed using X-ray Photoelectron Spectroscopy (XPS). The thickness of the MoL was assessed as ～1 nm, using Spectroscopic Ellipsometry and cross-sectional Transmission Electron Microscopy. XPS peak-shift analyses together with Kelvin Probe Force Microscopy revealed that the molecular surface modification reduced the surface potential of AlGaN by approximately 250 meV. Consequently, the Barrier height (ideality factor) of Ni Schottky diodes on AlGaN/GaN was increased (reduced) significantly from 0.91 ± 0.05 eV (2.5 ± 0.31) for Ni/AlGaN/GaN to 1.37 ± 0.03 eV (1.4 ± 0.29) for Ni/Zn-TPPOH/AlGaN/GaN. In addition, a noteworthy decrement in the reverse current from 2.6 ± 1.93 μA to 0.31 ± 0.19 nA at ?5 V (～10 000 times) was observed from Current-Voltage (I-V) measurements. This surface-modification process can be fruitful for improving the performance of AlGaN/GaN HEMTs, mitigating the adverse effects of polarization and surface states in these materials.
关键词： AlGaN/GaN,HEMT,Schottky barrier height,surface passivation,organic molecules,reverse current
更新于2025-09-10 09:29:36
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Electronic properties of Zigzag ZnO nanoribbons with Hydrogen and Magnesium passivations
摘要： In this study, the electronic properties of ZnO nanoribbons with zigzag edges (ZZnONr) have been investigated with Density Functional Theory (DFT). After a geometric optimization, the electronic band structures, the density of states (DOS) of ZZnONr passivated with Hydrogen (H) and Magnesium (Mg) atoms were calculated ZZnONr. It is shown that the increasing width of ZZnONrs has led to a decrement in energy band gap of the studied structures. While ZZnONr passivated with Mg for Zn-rich edge have not been shown a spin dependency, the structure passivated with Mg for O-rich edge have exhibited spin-dependent band structure. The energetically most stable structures have been determined as ZZnONr passivated with Mg for Zn-rich edge. ZZnONr passivated with Mg atoms for both edges have a graphene-like band structure especially for 8 and 10 atom width structures and this property of ZZnONrs could be important in terms of the electron transport for ZZnONrs.
关键词： ZnONr,Passivation,electronic properties,DFT
更新于2025-09-10 09:29:36
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High-performance black phosphorus field-effect transistors with long-term air-stability
摘要： Two-dimensional layered materials (2DLMs) are of considerable interest for high-performance electronic devices for their unique electronic properties and atomically thin geometry. However, the atomically thin geometry makes their electronic properties highly susceptible to the environment changes. In particular, some 2DLMs (e.g., black phosphorus (BP) and SnSe2) are unstable and could rapidly degrade over time when exposed to ambient conditions. Therefore, the development of proper passivation schemes that can preserve the intrinsic properties and enhance their lifetime represents a key challenge for these atomically thin electronic materials. Herein we introduce a simple, non-disruptive and scalable van der Waals passivation approach by using organic thin films to simultaneously improve the performance and air stability of BP field-effect transistors (FETs). We show that dioctylbenzothienobenzothiophene (C8-BTBT) thin films can be readily deposited on BP via van der Waals epitaxy approach to protect BP against oxidation in ambient conditions over 20 days. Importantly, the non-covalent van der Waals interface between C8-BTBT and BP effectively preserves the intrinsic properties of BP, allowing us to demonstrate high-performance BP FETs with a record-high current density of 920 μA/um, hole drift velocity over 1 ⅹ 107 cm/s, and on/off ratio of 104~107 at room temperature. This approach is generally applicable to other unstable two-dimensional (2D) materials, defining a unique pathway to modulate their electronic properties and realize high-performance devices through hybrid heterojunctions.
关键词： black phosphorus,saturation velocity,saturation current density,two-dimensional materials,passivation,field effect transistors
更新于2025-09-10 09:29:36