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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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Mechanism of Organic Solar Cell Performance Degradation upon Thermal Annealing of MoO <sub/>x</sub>
摘要： In this work we focus on P3HT:PC61BM bulk heterojunction (BHJ) devices with MoO3 at the hole extraction side of the BHJ which relies on the formation of a strong dipole at the BHJ/MoO3 interface, as a reference system that has been extensively studied. We have observed depending on when the annealing is performed during device fabrication, device performance either increased or decreased due to formation of a sharp or relatively diffuse interface respectively due to diffusion of MoOx into the BHJ. The measured strength of the dipole at this interface following thermal annealing correlated well with the width of the interface and device performance, with the sharper interface resulting in a stronger dipole and in improved device performance. This is expected to be a general phenomenon for evaporated coatings onto polymeric BHJ, regardless of the polymers involved.
关键词： Organic solar cell,Interface dipole,MoO3,Thermal annealing,Energy level alignment
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE 9th International Nanoelectronics Conferences (INEC) - Kuching, Malaysia (2019.7.3-2019.7.5)] 2019 IEEE 9th International Nanoelectronics Conferences (INEC) - ITO Islands as Floating Electrodes to Deposit Aligned Carbon Nanotubes for Photovoltaic Applications
摘要： Recently transparent conductive electrodes (TCEs) have attracted the interest of researchers due to their outstanding optical and electrical properties. Indium tin oxide (ITO) is an oxide material that combines the criteria of high conductance and transmittance. However, ITO is a non-flexible, brittle and expensive material. TCEs are commonly embedded in solar cells to perform high photon absorption and electron collection instantaneously. In this paper, an optimized TCE network is proposed to maintain TCEs’ conductivity and transparency and to improve their flexibility and ability to handle mechanical forces. The network is designed by aligning multi-walled carbon nanotubes (MWCNTs) on ITO speckled surface to form ITO-CNT through grid. The alignment mechanism is achieved by dielectrophoretic (DEP) force, where an electric field of 10V and 105 Hz is subjected to an ethanol/ MWCNT suspension to assemble the CNT across ITO’s floating electrodes.
关键词： Alignment,DEP,Thin film solar cell,TCEs,MWCNT
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
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Polarized Raman imaging of large area aligned semiconducting single‐walled carbon nanotubes
摘要： The current method of characterizing single-walled carbon nanotube (SWCNT) alignment utilizes single-point measurements of a few hundred square nanometers of polarized Raman spectroscopy to characterize an entire substrate of SWCNTs on the order of square centimeters. In this study, we demonstrate a new polarized Raman spectroscopy analyzation technique of orientation Raman imaging that images areas as large as 1 mm2. This provides a significantly more accurate representation of the spatial distribution in the alignment of any SWCNT film by increasing the measured area by 10 orders of magnitude over previous standard characterization techniques. Furthermore, this creates an “easy-to-see” visual representation of alignment based on optical anisotropy values. Improving the efficiency of characterizing alignment in SWCNT films via polarized Raman spectroscopy is an important step toward manufacturing scalable films of aligned SWCNTs.
关键词： polarized Raman imaging,polarized Raman spectroscopy,orientation image,carbon nanotube alignment,carbon nanotubes
更新于2025-09-12 10:27:22
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Luminescent europium-doped titania for efficiency and UV-stability enhancement of planar perovskite solar cells
摘要： Perovskite solar cells (PSCs) have demonstrated high power conversion efficiencies (PCEs) but poor stability against ultraviolet (UV) irradiation. Here, we report a one-pot synthesized luminescent europium-doped titania (Eu-TiO2) via chemical-bath deposition at low-temperature (70 oC) for planar PSCs, which enables simultaneous efficiency and UV-stability enhancement. We show that the Eu-TiO2 could effectively convert damaging UV photons into useful visible luminescence for additional light harvesting. A more optimal energy band alignment at the Eu-TiO2/perovskite interface leads to facilitated charge extraction and suppressed non-radiative recombination. The use of Eu-TiO2 in PSCs results in increased photocurrent and open-circuit voltage, yielding an enhanced PCE of 21.40% with relative to pristine TiO2 device (19.22%). More importantly, the Eu-TiO2 devices exhibit remarkably improved UV stability, retaining 75% of the initial PCE after exposing to UV illumination for 500 hours, while the devices with pristine TiO2 lost the majority of their original PCEs in 150 hours. As a proof-of-concept, we further demonstrate the scalability of our method by fabricating a large-area Eu-TiO2 film of 64 cm2 showing excellent uniformity.
关键词： band alignment,planar perovskite solar cells,down-shifting,europium-doped titanium dioxide,UV stability
更新于2025-09-12 10:27:22
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The Impact of Mobile Ions on the Steady State Performance of Perovskite Solar Cells
摘要： Mobile ions in perovskite solar cells induce many unique transient phenomena, while their influence under steady-state, the primary operating condition, has received little attention. Therefore, in this work we employ ionic-drift diffusion models to assess how the steady-state distribution of mobile ions affects the photogenerated carrier collection, and their redistribution due to dopants and energy band alignment. We demonstrate that mobile ions can transform the carrier transport mechanism from a combination of drift and diffusion to transport by diffusion only, which only impacts the device efficiency if the carrier mobility-lifetime product is limited due to increased transport losses and changed recombination dynamics. A high concentration of dopants is also required in perovskite devices for such doping to have a measurable impact while the energy alignment of the transport layers, on the other hand, can in principle result in a doping-like effect, which generally causes adverse consequences for cell efficiency.
关键词： dopants,steady-state performance,perovskite solar cells,energy band alignment,mobile ions,carrier transport
更新于2025-09-12 10:27:22
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Laser Scanning Confocal Image Alignment Assists Sub-micron Accuracy Micro-assembly
摘要： The image resolution of the ordinary optical microscope in the assembly system can’t break through the optical diffraction limit, and the accuracy of alignment detection can’t reach the sub-micron level. So we build the micro assembly system based on the principle of confocal image alignment to solve the above problems. In this paper, the basic principle and system of confocal image alignment assembly are studied, and the levelling calibration method of the platform is also studied. After the calibration, the alignment resolution of the micro assembly system based on the principle of confocal image alignment can reach 0.5μm.The confocal image alignment principle is verified by the assembly application experiment of inserting a 125-μm-diameter optical fiber into a 127-μm-diameterglass micro tubule. The confocal image alignment principle and the calibration method can greatly improve the accuracy and efficiency of the micro assembly.
关键词： Precision microassembly,Submicron precision,Confocal alignment,Levelling calibration
更新于2025-09-12 10:27:22
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Valence-State Controllable Fabrication of Cu <sub/> 2– <i>x</i> </sub> O/Si Type-II Heterojunction for High-Performance Photodetectors
摘要： Cuprite, nominally cuprous oxide (Cu2O) but more correctly Cu2-xO, is widely used in optoelectronic applications due to its natural p-type, nontoxicity and abundant availability. However, the photoresponsivity of Cu2O/Si photodetectors (PDs) has been limited by the lack of high-quality Cu2-xO films. Herein, we report a facile room-temperature solution method to prepare high-quality Cu2-xO films with controllable x value which were used as hole selective transport layers in crystalline n-type silicon based heterojunction PDs. The detection performance of Cu2-xO/Si PDs exhibits a remarkable improvement via reducing the x value, resulting in the optimized PDs with high responsivity of 417 mA W-1 and fast response speed of 1.3 μs. Furthermore, the performance of the heterojunction PDs can be further improved by designing the pyramidal silicon structure, with enhanced responsivity of 600 mA W-1 and response speed of 600 ns. The superior photodetecting performance of Cu2-xO/n-Si heterojunctions is attributed to (i) the matched energy level band alignment, (ii) the low trap states in high-quality Cu2O thin films, (iii) the excellent light trapping. We expect the low-cost, highly efficient solution process would be of great convenience for large-scale fabrication of the Cu2-xO thin films and broaden the applications of Cu2-xO based optoelectronic devices.
关键词： photodetector,energy band alignment,Cuprous oxide,solution method,heterojunction
更新于2025-09-12 10:27:22
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Elucidating the effects of guest-host energy level alignment on charge transport in phosphorescent OLEDs
摘要： The correct choice of guest and host molecules in the light-emitting layer is essential for developing high performance phosphorescent organic light emitting devices. However, the effects of the energy level alignment between the guest and the host are yet to be fully elucidated. In this Letter, we use kinetic Monte Carlo simulations to investigate guest-host systems in which the energy gap of the guest and host is fixed, and only the relative energies of the ionization potential/electron affinity are changed to elucidate their effect on charge transport. It was determined that the mobility balance in the blend was sensitive to the energy level alignment, allowing balanced active layer mobility to be achieved despite the hole and electron mobilities being different by around one order of magnitude. It was also found that the mobility of the faster carrier was more sensitive to the energy level alignment than that of the slower carrier due to reduced slower carrier thermalization under deep charge trapping on the guest.
关键词： guest-host energy level alignment,phosphorescent OLEDs,kinetic Monte Carlo simulations,charge transport
更新于2025-09-12 10:27:22