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Excitonic Effects and Impuritya??Defect Emission in GaAs/AlGaAs Structures Used for the Production of Mid-IR Photodetectors
摘要： A series of undoped GaAs/AlxGa1 – xAs multiple quantum well heterostructures, whose doped analogs are used for the production of photodetectors operating in the spectral range 8–12 μ m, is fabricated by molecular-beam epitaxy. For the heterostructures, the spectral position of absorption lines corresponding to the allowed transitions between quantum-confined electron and hole levels in GaAs layers is established. The influence of impurity–defect states on the luminescence and absorption spectra of quantum wells is studied. The excitonic corrections for the allowed transitions are determined in relation to the quantum-well width and the aluminum content in the barrier layers. The role of excitonic effects in restoring the structure of single-electron states from interband-absorption spectra (luminescence-excitation spectra) and the relationship between these states and the working region of IR photodetectors based on GaAs/AlxGa1 – xAs quantum wells are discussed.
关键词： quantum well,IR detector,exciton,luminescence
更新于2025-09-19 17:13:59
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Improvement of Exciton Collection and Light-Harvesting Range in Ternary Blend Polymer Solar Cells Based on Two Non-Fullerene Acceptors
摘要： A non‐fullerene molecule named Y6 was incorporated into a binary blend of PBDB‐T and IT‐M to further enhance photon harvesting in the near‐infrared (near‐IR) region. Compared with PBDB‐T/IT‐M binary blend devices, PBDB‐T/IT‐M/Y6 ternary blend devices exhibited an improved short‐circuit current density (JSC) from 15.34 to 19.09 mA cm?2. As a result, the power conversion efficiency (PCE) increased from 10.65% to 12.50%. With an increasing weight ratio of Y6, the external quantum efficiency (EQE) was enhanced at around 825 nm, which is ascribed to the absorption of Y6. At the same time, EQE was also enhanced at around 600–700 nm, which is ascribed to the absorption of IT‐M, although the optical absorption intensity of IT‐M decreased with increasing weight ratio of Y6. This is because of the efficient energy transfer from IT‐M to Y6, which can collect the IT‐M exciton lost in the PBDB‐T/IT‐M binary blend. Interestingly, the EQE spectra of PBDB‐T/IT‐M/Y6 ternary blend devices were not only increased but also red‐shifted in the near‐IR region with increasing weight ratio of Y6. This finding suggests that the absorption spectrum of Y6 is dependent on the weight ratio of Y6, which is probably due to different aggregation states depending on the weight ratio. This aggregate property of Y6 was also studied in terms of surface energy.
关键词： non‐fullerene,exciton harvesting,surface energy,ternary blend solar cells,energy transfer
更新于2025-09-19 17:13:59
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Strong coupling of two quantum dots with a microcavity in the presence of an external and tilted magnetic field
摘要： Including an external magnetic field B in a Tavis-Cummings model enables us to consider four exciton states in each quantum dot, two brights and two darks. With a continuous and incoherent pump to a cavity, we explore the conditions of occupation and emission as a function of B. We have found that although the dark excitons are optically inactive, these show a trace of emission as a result of both the strong coupling between light and matter and the interaction between bright and dark exciton states mediated by the magnetic field. Further, tuning one of the quantum dots at resonance with the cavity, we report the set of parameters that allows us to change the resonance condition between exciton states from different quantum dots, namely, we use the magnetic field as a control parameter to select which exciton state and which quantum dot will be mostly coupled to the cavity.
关键词： strong coupling,magnetic field,quantum dots,exciton states,microcavity
更新于2025-09-19 17:13:59
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Trade‐Off between Exciton Dissociation and Carrier Recombination and Dielectric Properties in Y6‐Sensitized Nonfullerene Ternary Organic Solar Cells
摘要： Organic photovoltaics (OPVs) have emerged as a promising renewable energy generation technology in past decades. However, the deep understanding of the details in exciton dissociation and carrier recombination in ternary organic solar cells (OSCs) is still lacking. Herein, a novel ternary OSC based on a PTB7-Th:Y6:ITIC blend with a power conversion efficiency (PCE) enhancement of 29% is reported. A trade-off is surprisingly found to exist between the exciton dissociation and carrier recombination process. The addition of nonfullerene acceptor Y6 in the ternary blend is found to create an efficient exciton dissociation process but accelerates the free carrier recombination process. Dielectric properties are also studied for ternary OSCs. The addition of Y6 into the binary blend is found to tune down the dielectric constant of the active layer and as a result accelerates the carrier recombination. The best performance is obtained for PTB7-Th:Y6(5 wt%):ITIC(95 wt%)-based ternary devices. In addition to its balanced charge carrier mobility and efficient charge extraction process, PTB7-Th:Y6(5 wt%):ITIC(95 wt%)-based ternary devices reach a balance in the trade-off between the exciton dissociation and carrier recombination process and thus achieve the highest short-circuit current density (Jsc) value.
关键词： nonfullerene,carrier recombination and dielectric constants,ternary,organic solar cells,exciton dissociation
更新于2025-09-19 17:13:59
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Nonconfinement Structure Revealed in Dion–Jacobson Type Quasi‐2D Perovskite Expedites Interlayer Charge Transport
摘要： Dion–Jacobson (DJ) type 2D perovskites with a single organic cation layer exhibit a narrower distance between two adjacent inorganic layers compared to the corresponding Ruddlesden–Popper perovskites, which facilitates interlayer charge transport. However, the internal crystal structures in 2D DJ perovskites remain elusive. Herein, in a p-xylylenediamine (PDMA)-based DJ perovskite bearing bifunctional NH3+ spacer, the compression from confinement structure (inorganic layer number, n = 1, 2) to nonconfinement structure (n > 3) with the decrease of PDMA molar ratio is unraveled. Remarkably, the nonconfined perovskite displays shorter spacing between 2D quantum wells, which results in a lower exciton binding energy and hence promotes exciton dissociation. The significantly diminishing quantum confinement promotes interlayer charge transport leading to a maximum photovoltaic efficiency of ≈11%. Additionally, the tighter interlayer packing arising from the squeezing of inorganic octahedra gives rise to enhanced ambient stability.
关键词： exciton,planar perovskite solar cells,nonconfinement structures,Dion–Jacobson,quasi-2D perovskite
更新于2025-09-19 17:13:59
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Influence of nonradiative Auger process in the lanthanide complexes lifetime near interfaces in organic light-emitting diode structures
摘要： The low efficiency of organic light-emitting diodes based on lanthanide complexes is generally attributed to the triplet-triplet annihilation processes in the regime of high concentration of excited states caused by their long lifetimes and optical losses near the interfaces of multilayer device structures. Despite the enormous effort to synthesize short-lived complexes and minimize the optical losses in the interfaces, it remains insufficient in understanding the exciton recombination processes that reduce the lifetime of these complexes. Herein, we investigated the influence of the exciton recombination processes on a Tb complex (Tb-C) lifetime in the regime of a highly excited state concentration as a function of the distance between the carrier layer and the interface by using a typical organic light-emitting diode structure. Our results show that a 10 nm-thick Alq3 layer decreases the exciton lifetime of the Tb-C, increasing approximately by 16 times the spontaneous emission decay rate of triplet exciton. The effects of interference and optical losses at the metallic interface contribute actively to the modulation of the emission intensity and lifetime decay. However, these effects alone do not explain the significant increase in the emission decay rate. The nonradiative Auger process at the Alq3/Tb-C interface seems to be largely accountable for the Tb-C lifetime reduction as the energy released by the terbium ion occurs by the excitation of an adjacent electron at higher energy. Furthermore, we propose a simple theoretical model to explain the observed effects. These results can provide a new approach to reduce the lanthanide complexes’ lifetime through the Auger electron process near the interface and thus improve the performance of organic light-emitting diodes.
关键词： exciton recombination,Auger process,organic light-emitting diodes,lifetime reduction,lanthanide complexes
更新于2025-09-19 17:13:59
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Strong exciton-photon coupling in organic microcavity electroluminescence devices with thiophene/phenylene co-oligomer derivatives
摘要： Organic electroluminescence (EL) devices with surface-emitting microcavity structure were fabricated using vapor-deposited films of thiophene/phenylene co-oligomer derivatives, aiming at polariton formation under electrical excitation. Owing to strong coupling between excitons and photons in the device, we demonstrated the formation of cavity polaritons with a large Rabi-splitting energy (2?Ω = 250 meV). Furthermore, efficient relaxation into the bottom of lower polariton branch was confirmed from angle-resolved EL spectra. In excitation-density dependence, the luminance of microcavity EL devices showed a superlinear increase with an elevation of current density indicating a contribution of triplet excitons.
关键词： polariton,exciton-photon coupling,organic electroluminescence,microcavity,Rabi-splitting
更新于2025-09-19 17:13:59
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Nonlinear polaritons in a monolayer semiconductor coupled to optical bound states in the continuum
摘要： Optical bound states in the continuum (BICs) provide a way to engineer very narrow resonances in photonic crystals. The extended interaction time in these systems is particularly promising for the enhancement of nonlinear optical processes and the development of the next generation of active optical devices. However, the achievable interaction strength is limited by the purely photonic character of optical BICs. Here, we mix the optical BIC in a photonic crystal slab with excitons in the atomically thin semiconductor MoSe2 to form nonlinear exciton-polaritons with a Rabi splitting of 27 meV, exhibiting large interaction-induced spectral blueshifts. The asymptotic BIC-like suppression of polariton radiation into the far field toward the BIC wavevector, in combination with effective reduction of the excitonic disorder through motional narrowing, results in small polariton linewidths below 3 meV. Together with a strongly wavevector-dependent Q-factor, this provides for the enhancement and control of polariton–polariton interactions and the resulting nonlinear optical effects, paving the way toward tuneable BIC-based polaritonic devices for sensing, lasing, and nonlinear optics.
关键词： nonlinear exciton-polaritons,MoSe2,Rabi splitting,photonic crystal slab,Optical bound states in the continuum
更新于2025-09-19 17:13:59
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Colloidal Assembly of Aua??Quantum Dota??Au Sandwiched Nanostructures with Strong Plasmona??Exciton Coupling
摘要： Strong plasmon-exciton coupling could occur in hybrid metal-dye/semiconductor nanostructures, where the fast energy exchange between plasmons and excitons leads to two new eigenmodes of the system, known as Rabi splitting. In experiment, strongly coupled nanosystems are difficult to obtain because they require some strict conditions, such as low plasmonic damping, small plasmon mode volume, and good spectral overlap. This work demonstrates strongly coupled metal-semiconductor nanostructures can be constructed using colloidal assembly. Specifically, sandwiched Au-QD-Au nanostructures were created through the assembly of Au nanoparticles and colloidal quantum dots (QDs). The sizes of the QDs and the assembly conditions were varied to control the mode volume of the plasmonic cavity formed between the two Au nanoparticles. With decreased gap size, Rabi splitting was observed in both dark-field scattering and fluorescence spectra of single Au-QD-Au nanostructures. Theoretical simulations revealed that the strong coupling occurred between the excitons and the octupolar plasmon modes.
关键词： Au-QD-Au nanostructures,Rabi splitting,octupolar plasmon modes,plasmon-exciton coupling,colloidal assembly
更新于2025-09-19 17:13:59
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Fundamental Limit of the Emission Linewidths of Quantum Dots: An Ab Initio Study of CdSe Nanocrystals
摘要： The emission linewidth of a semiconducting nanocrystal (NC) significantly affects the performance in light-emitting applications but its fundamental limit is still elusive. Herein we analyze exciton-phonon coupling (EPC) from Huang-Rhys (HR) factors using ab initio calculations, and compute emission line shapes of CdSe NCs. When surface traps are absent, acoustic modes are found to dominate EPC. The computed linewidths are mainly determined by the size of NCs, being largely insensitive to the shape and crystal structure. Linewidths obtained in this work are much smaller than most measurements on the homogeneous linewidth, but they are consistent with a CdSe/CdxZn1?xSe (core/shell) NC [Park et al. Nat. Mater. 2019, 18, 249-255]. Based on this comparison, it is concluded that the large linewidths in most experiments originated from internal fields by surface (or interface) traps or quasi-type Ⅱ band alignment that amplify EPC. Thus, the present results on NCs with ideal passivation provide the fundamental minimum of homogeneous linewidths, indicating that only the CdSe/CdxZn1?xSe NC has achieved this limit through well-controlled synthesis of the shell structure. To further verify the role of internal fields, we model NCs with charged surface defects. We find that the internal field significantly increases HR factors and linewidths, in reasonable agreements with experiments on single cores. By revealing the fundamental limit of emission linewidths of quantum dots, this work will pave the way to engineering quantum dots with ultrasharp spectrum.
关键词： nanocrystals,photoluminescence,homogeneous linewidth,exciton-phonon coupling,surface traps,density functional theory,electroluminescence,quantum dots
更新于2025-09-19 17:13:59