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Assessing the roles of Cu- and Ag-deficient layers in chalcopyrite-based solar cells through first principles calculations
摘要： Chalcopyrites are a demonstrated material platform for realizing efficient thin-film photovoltaics, with the most well known Cu(In,Ga)Se2 (CIGS)-based solar cells exceeding 23%. Several factors, including flexibility in tuning the absorber bandgap, enhanced surface treatments, and the electrically benign nature of common defects are responsible for the existing high performance and future promise in chalcopyrite-based photovoltaic devices. The introduction of Cu-poor phases (also known as ordered-vacancy compounds or OVCs) between the absorber and buffer layers in CIGS solar cells is known to enhance device performance; however, the overall properties and role of OVCs remain poorly understood. Using first principles calculations based on the density functional theory with screened hybrid functionals, we explore the electronic structure and stability of OVCs and their band offsets with defect-free chalcopyrite layers in Cu- and Ag-based compounds (ABX2 where A ? Cu, Ag; B ? In, Ga, Al; and X ? S, Se). Using AB3X5 and AB5X8 stoichiometries as model OVC systems, we report on the variation of the bandgap with the A/B ratio and discuss the trends in other Cu- and Ag-based chalcopyrites beyond CuInSe2. We find that the valence and conduction bands are lower in energy in OVCs with respect to the parent ABX2 chalcopyrite owing to a reduced p–d interaction between X and A atoms. We additionally perform device-level simulations to assess the implications of the results, finding that the valence band offsets of OVCs are favorable, while the conduction band offsets of chalcopyrites beyond CuInSe2-based absorbers may be detrimental in conventional solar cell device designs.
关键词： solar cells,density functional theory,chalcopyrites,band offsets,ordered-vacancy compounds
更新于2025-09-19 17:13:59
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Chlorine Vacancy Passivation in Mixed Halide Perovskite Quantum Dots by Organic Pseudohalides Enables Efficient Rec. 2020 Blue Light-Emitting Diodes
摘要： Blue-emitting perovskites are easily attainable by precisely tuning the halide ratio of mixed halide (Br/Cl) perovskites (MHPs). However, the adjustable halide ratio also hinders the passivation of Cl vacancies – the main source of trap states leading to inferior performance blue MHP light-emitting diodes (LEDs). Here, we report a strategy to passivate Cl vacancies in MHP quantum dots (QDs) using non-polar-solvent-soluble organic pseudohalide (n-dodecylammonium thiocyanate (DAT)), enabling blue MHP LEDs with greatly enhanced efficiency. Density-functional-theory calculations reveal that the thiocyanate (SCN-) groups fill in the Cl vacancies and remove electron traps within the bandgap. DAT-treated CsPb(BrxCl1-x)3 QDs exhibit near unity (~100%) photoluminescence quantum yields; and their blue (~470 nm) LEDs are spectrally stable with an external quantum efficiency (EQE) of 6.3% – a record for perovskite LEDs emitting in the 460-480 nm range relevant to Rec. 2020 display standards – and a half-lifetime of ~99 s.
关键词： light-emitting diodes,organic pseudohalides,blue emission,perovskite,chlorine vacancy passivation,quantum dots
更新于2025-09-19 17:13:59
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Nonvolatile Resistive Switching Memory Device Employing CdSe/CdS Core/Shell Quantum Dots as an Electrode Modification Layer
摘要： Accompanied with great advantages in various fields of performance, memristors show huge potential in the next generation of mainstream storage devices. However, their random distribution of resistance switching voltage has always been one of the problems in applications. In this present work, a nonvolatile resistive switching memory device was proposed, which employed CdSe/CdS core/shell quantum dots (QDs) assembled as an electrode modification layer with the device configuration of Pt/CdSe-CdS QDs/TaOx/Ta. The device possesses multiple excellent resistance switching characteristics such as lower and more consistent set/reset threshold voltage and better endurance performance, which is considered as the effect of the electrode modification layer based CdSe/CdS core/shell QDs. A model with uneven QDs/Pt electrode interface was put forward to explain the different resistance switching behaviors, which may be beneficial to the development of existing research about memristors based on metal oxides and quantum dots.
关键词： Migration,Oxygen vacancy,Schottky interface,CdSe/CdS core/shell quantum dots,resistive switching
更新于2025-09-19 17:13:59
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Ultrathin Self-feeding Metasurface with Broadband Polarization Conversion and Electromagnetic Emission
摘要： A model for controlling the two-dimensional distribution of negatively charged nitrogen-vacancy (NV?) fluorescent centers near the surface of a diamond crystal is presented, using only a microwave plasma-assisted chemical vapor deposition (CVD) method. In this approach, a CVD diamond layer is homoepitaxialy grown via microwave plasma-assisted CVD using an isotopically enriched methane (12CH4 ), hydrogen (H2 ), and nitrogen (N2 ) gas mixture on patterned diamond (0 0 1). When the surface is imaged by means of confocal microscope photoluminescence mapping, fine grooves are observed to have been generated artificially on the diamond surface. NV? centers are found to be distributed selectively into these grooves. These results demonstrate an effective means for the formation of NV? centers of selectable size and density via microwave plasma-assisted CVD, with potential application in the production of diamond quantum sensors.
关键词： doping,nitrogen-vacancy centers,homoepitaxial,groove structure,Diamond,microwave plasma-assisted chemical vapor deposition
更新于2025-09-19 17:13:59
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Modulation of Plasticity of All-metal Oxide Synaptic Transistor via Laser Irradiation
摘要： Artificial intelligence device mimicking human brains is the foundation for building future artificially neural networks. A key step to mimic biological neural systems is the modulation of synaptic weight, which is mainly achieved by various engineering approaches with materials design or modification of device structure. Here, we realized the modulation of synaptic weight of Ta2O5/ITO based all-metal oxide synaptic transistor via laser irradiation. Prior to the deposition of active layer and electrodes, fs-laser was induced to irradiate on the surface of insulator layer. The typical synaptic characteristics such as excitatory post synaptic current (EPSC), paired pulse facilitation (PPF) and long term potentiation (LTP) were successfully simulated under different laser intensities and scanning rates. Particularly, we demonstrated for the first time that laser irradiation could control the amount of oxygen vacancies in the Ta2O5 thin film, leading to the precise modulation of synaptic weight. Our research provides an instantaneous(<1s), convenient and low-temperature approach to improve synaptic behaviors, which would be promising for neuromorphic computing hardware design.
关键词： synaptic transistor,laser irradiation,oxygen vacancy,Ta2O5
更新于2025-09-19 17:13:59
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Halogen Vacancies Enable Ligand‐Assisted Self‐Assembly of Perovskite Quantum Dots into Nanowires
摘要： Interest has been growing in defects of halide perovskites in view of their intimate connection with key material optoelectronic properties. In perovskite quantum dots (PQDs), the influence of defects is even more apparent than in their bulk counterparts. By combining experiment and theory, we report herein a halide-vacancy-driven, ligand-directed self-assembly process of CsPbBr3 PQDs. With the assistance of oleic acid and didodecyldimethylammonium sulfide, surface-Br-vacancy-rich CsPbBr3 PQDs self-assemble into nanowires (NWs) that are 20–60 nm in width and several millimeters in length. The NWs exhibit a sharp photoluminescence profile ( (cid:2) 18 nm full-width at-half-maximum) that peaks at 525 nm. Our findings provide insight into the defect-correlated dynamics of PQDs and defect-assisted fabrication of perovskite materials and devices.
关键词： self-assembly,perovskite quantum dot,halide vacancy,nanowire,CsPbBr3
更新于2025-09-19 17:13:59
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Phononic-waveguide-assisted steady-state entanglement of silicon-vacancy centers
摘要： Multiparticle entanglement is of great significance for quantum metrology and quantum information processing. We present here an efficient scheme for generating stable multiparticle entanglement in a solid-state setup, where an array of silicon-vacancy centers are embedded in a quasi-one-dimensional acoustic diamond waveguide. In this scheme, the continuum of phonon modes induces a controllable dissipative coupling among the SiV centers. We show that, by an appropriate choice of the distance between the SiV centers, the dipole-dipole interactions can be switched off due to destructive interference, thus realizing a Dicke superradiance model. This gives rise to an entangled steady state of SiV centers with high fidelities. The protocol provides a feasible setup for the generation of multiparticle entanglement in a solid-state system.
关键词： Multiparticle entanglement,quantum information processing,acoustic diamond waveguide,quantum metrology,silicon-vacancy centers,Dicke superradiance model
更新于2025-09-19 17:13:59
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Improve the quality of HC(NH2)2PbIxBr3?x through iodine vacancy filling for stable mixed perovskite solar cells
摘要： Formamidinium-based (FA-based) with broader light absorption spectra have been attracted enormous attention. However, the FAI-PbI2-DMSO intermediate anisotropic ?bers can easily produce yellow δ-FAPbI3 and uncontrolled excess PbI2, which signi?cantly increased the defect and reducing the reproducibility of devices. Furthermore, the iodine defect in polycrystalline ?lms would enlarge the perovskite tolerance factor and trigger ion migration. This ion migration within perovskite layer leads to device degradation and impedes large scale commercial applications. Herein, we develop a vacancy ?lling (VF) method to repair iodine vacancy as well as yield pure black phase FA perovskite. Upon post treatment with FABr, the point defects on surface and the notorious δ-FAPbI3 caused by lager tolerance are removed though vancancy fulling. The champion of obtained FAPbIxBr3?x device presents the power conversion e?ciency (PCE) up to 18.2% and could remain > 85% of the original PCE after 20 days in the dark at room temperature (10–25 °C) and humidity of 10–40%. Therefore, this VF technique provides an interesting entry for obtaining high pure black perovskite phase.
关键词： Iodine vacancy,Nonperovskite phase,Formamidinium perovskite solar cells,Post-treating
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Fabrication of High Quality Quantum Emitters in Diamond Nanostructures
摘要： As the field of solid-state quantum engineering matures, it is increasingly necessary to produce quantum emitters with narrow optical transitions and long spin coherence times aligned to nanophotonic structures. The nitrogen-vacancy (NV) defect center in diamond is a well-suited candidate owing to a spin ground state with a long coherence time, nearby nuclear spins for quantum memories, and spin-selective optical transitions allowing for efficient optical spin initialization and readout. We demonstrate an emitter-device alignment technique enabling fabrication of photonic devices registered to NVs. The alignment method relies on autonomously imaging emitters and registering them relative to an on-chip coordinate system. This technique can be performed on a large variety of emitters. The repeatability of this method suggests a spatial accuracy of 50 nm. The ability to navigate a sample autonomously facilitates data collection on a large number of NVs, thus permitting statistical analyses. We utilized this approach to correlate the NV’s host nitrogen isotope with the optical linewidth of the emitter to understand the effects of implantation. As shown in Fig. 1a, the data indicate that the coherent, narrow-linewidth NVs are formed from naturally abundant nitrogen (14N), whereas the implanted nitrogens (15N), on average, yield broader linewidth NVs. The implanted 15NVs also exhibit larger axial and transverse strains suggesting that damage was produced near the emitter. We attribute the broad linewidths of implanted 15NVs to a more volatile local environment generated by local damage resulting from the ion implantation process.
关键词： diamond nanostructures,nanophotonic structures,nitrogen-vacancy center,spin coherence,quantum emitters
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Multi-Qubit Registers of Individually Addressable Solid-State Defect Centers
摘要： Mesoscopic ensembles of qubits offer a platform for near-term applications in quantum technologies, as well as for studying many-body physics. Key in exploiting these systems is the ability to coherently control constituent qubits in a manner that leaves the quantum states of neighboring qubits unperturbed. Atom-like emitters in solids have emerged as a promising platform for computing, communications, and sensing. In particular, their long coherence times, coherent optical transitions, and the ability to couple to nearby long-lived nuclear spins make them excellent candidates for building medium-scale registers of coupled qubits. Here, we present progress towards producing and controlling such individually addressable ensembles. Our approach relies on the natural inhomogeneous distribution of optical transitions for solid-state color centers. This distribution allows us to excite individual centers even in tightly-grouped clusters. With this, we first demonstrate super-resolution localization and readout of individual nitrogen vacancy (NV) centers in diamond. We probe a system of three NV centers, demonstrating localization with a mean precision of 0.74 nm. While super-resolution imaging of NV centers has been achieved with other techniques, our approach uniquely allows for individual readout of single NVs in a cluster in a manner that maintains the states of nearby spins. We perform simultaneous control of two spin populations in a cluster of NVs, demonstrating preservation of coherence of one population during the optical readout of another. Lastly, we discuss recent work towards scalable creation of such clusters and techniques for producing systems of coupled spins with various defect centers.
关键词： spin-spin coupling,quantum technologies,super-resolution localization,qubits,solid-state color centers,nitrogen vacancy centers,many-body physics,atom-like emitters
更新于2025-09-16 10:30:52