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Ultrafast Hole Transfer and Carrier Transport Controlled by Nanoscale-Phase Morphology in Nonfullerene Organic Solar Cells
摘要： Nonfullerene acceptors (NFAs) have attracted great attention in high-efficiency organic solar cells (OSCs). While the effect of molecular properties including structures and energetics on charge transfer have been extensively investigated, the effect of macroscopic phase properties is yet to be revealed. Here we have performed a correlation study of the nanoscale phase morphology on photoexcited hole transfer (HT) process and photovoltaic performance, by combing ultrafast spectroscopy with high temporal resolution and photo-induced force microscopy (PiFM) with high spatial and chemical resolution. In PM6/IT-4F, we observe a biphasic HT behavior with a minor ultrafast (< 100 fs) interfacial process and a major diffusion mediated HT process till ~ 100 ps, which depends on phase segregation strongly. Because of the interplay between charge transfer and transport, a compromised domain size of 20 ~ 30 nm for NFAs shows best performance. This study highlights the critical role of phase morphology in high-efficiency OSCs.
关键词： photo-induced force microscopy,phase morphology,ultrafast spectroscopy,organic solar cells,hole transfer,Nonfullerene acceptors
更新于2025-09-19 17:13:59
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Ultrafast preparation of Europium(III) and Terbium(III) activated LaSr2F7 nanoparticles for white LEDs and anti-counterfeiting mark
摘要： Tunable color-emitting LaSr2F7 nanoparticle-based phosphor materials with single- or co-doped trivalent rare-earth ions (Eu3t/Tb3t) were synthesized via an ultrafast chemical precipitation technique. When Eu3t and Tb3t ions were doped into the LaSr2F7 nanoparticles, the photoluminescence behaviors were investigated and showed characteristic red and green emissions in their respective regions. Under 393 nm excitation, the LaSr2F7:xEu3t nanoparticles revealed the dominant red emission band (5D0 / 7F1) of Eu3t ions while the optimum doping concentration was obtained at 0.4 mol, indicating a quantum yield (QY) of 24.5%. Likewise, the LaSr2F7:yTb3t nanoparticles showed the f-f transition of Tb3t ions and an intense green-emission peak at 543 nm (5D4 / 7F5) was observed under 352 nm of excitation wavelength and the predominant doping concentration was 0.5 mol and the QY was estimated to be about 33.4%. By increasing the Eu3t ion concentration in the optimized LaSr2F7:Tb3t phosphors, the color emissions were turned from yellow to red under 365 nm excitation and the existed energy transfer ef?ciency in between the Tb3t and Eu3t ions was analyzed. Furthermore, the red-, green- and warm white-emitting devices were also fabricated by utilizing the optimal single- and co-doped samples for covering NUV chips. Ultimately, the LaSr2F7:Eu3t and LaSr2F7:Tb3t nanoparticles were further applied to a high-security ink for stabile anti-counterfeiting mark.
关键词： White LEDs,Ultrafast synthesis,Anti-counterfeiting mark,Energy transfer
更新于2025-09-19 17:13:59
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Switchable and dual-wavelength ultrafast fibre lasers with an MoTe <sub/>2</sub> -based saturable absorber
摘要： Based on monolayer MoTe2 film, we have proposed a mode-locked fibre laser delivering single-wavelength and dual-wavelength solitons at the telecommunication band. The saturable absorber (SA) is synthesized by coating monolayer MoTe2 film on the pinhole of fibre pigtail. The experimental results show that our soliton lasers can work at the single- and dual-wavelength states, respectively, by appropriately adjusting the polarization controller. The proposed laser can work stably at the mode-locking state for several hours, indicating that monolayer MoTe2 film is an excellent SA material for ultrafast optics.
关键词： ultrafast fibre laser,two dimensional materials,Saturable absorber
更新于2025-09-19 17:13:59
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Hierarchical Laser-Patterned Silver/Graphene Oxide Hybrid SERS Sensor for Explosive Detection
摘要： We demonstrate an ultrafast laser-ablated hierarchically patterned silver nanoparticle/graphene oxide (AgNP/GO) hybrid surface-enhanced Raman scattering (SERS) substrate for highly sensitive and reproducible detection of an explosive marker 2,4-dinitrotoluene (2,4-DNT). A hierarchical laser-patterned silver sheet (Ag?S) is achieved by ultrafast laser ablation in air with pulse energies of 25, 50, and 100 μJ. Multiple laser pulses at a wavelength of 800 nm and a pulse repetition rate of 50 fs at 1 kHz are directly focused on Ag?S to produce and deposit AgNPs onto Ag?S. The surface morphology of ablated Ag?S was evaluated using atomic force microscopy, optical pro?lometry, and ?eld emission scanning electron microscopy (FESEM). A rapid increase in the ablation rate with increasing laser energy was observed. Selected area Raman mapping is performed to understand the intensity and size distribution of AgNPs on Ag?S. Further, GO was spin-coated onto the AgNPs produced by ultrafast ablation on Ag?S. The hierarchical laser-patterned AgNP/GO hybrid structure was characterized using FESEM, high-resolution transmission electron microscopy, X-ray di?raction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Further, hierarchical laser-patterned AgNP/GO hybrid structures have been utilized as SERS-active substrates for the selective detection of 2,4-DNT, an explosive marker. The developed SERS-active sensor shows good stability and high sensitivity up to picomolar (pM) concentration range with a Raman intensity enhancement of ～1010 for 2,4-DNT. The realized enhancement of SERS intensity is due to the cumulative e?ect of GO coated on Ag?S as a proactive layer and AgNPs produced by ultrafast ablation.
关键词： silver nanoparticle/graphene oxide (AgNP/GO) hybrid,ultrafast laser ablation,explosive detection,surface-enhanced Raman scattering (SERS),2,4-dinitrotoluene (2,4-DNT)
更新于2025-09-19 17:13:59
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Ultrafast Photodetector by Integrating Perovskite Directly on Silicon Wafer
摘要： Single crystal (SC) perovskite is currently a promising material due to its high quantum efficiency and long diffusion length. However, the reported perovskite photodection range (< 800 nm) and response time (> 10 μs) are still limited. Here, to promote the development of perovskite-integrated optoelectronic devices, this work demonstrates wider photodection range and shorter response time perovskite photodector by integrating the SC CH3NH3PbBr3 (MAPbBr3) perovskite on silicon (Si). The Si/MAPbBr3 heterojunction photodetector with an improved interface exhibits high performances including high speed, broad spectrum, and long-term stability. To our best knowledge, the measured detectable spectrum (405 nm-1064 nm) largely expands the widest response range reported in previous perovskite-based photodetectors. In addition, the rise time is as fast as 520 ns, which is comparable with commercial germanium photodetectors. Moreover, the Si/MAPbBr3 device can maintain excellent photo-current performance up to 3 months. Furthermore, typical grey-scale face imaging is realized by scanning the Si/MAPbBr3 single-pixel photodetector. This work of ultrafast photodetector by directly integrating perovskite on Si can promote advances in next-generation integrated optoelectronic technology.
关键词： photodetectors,integrations,single crystal perovskites,CH3NH3PbBr3,ultrafast
更新于2025-09-19 17:13:59
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Experimental study on two-phase boiling in wavy copper microchannels fabricated with ultrafast laser micromachining
摘要： In this study, the sinusoidal wavy (SW) copper microchannels with triangular cross section were fabricated with the ultrafast laser micromachining approach. The flow boiling of de-ionized water in SW microchannel were experimentally studied under mass fluxes of 43.43-217.15 kg/(m2s) and heat fluxes of 0-590 kW/m2. The flow patterns in the SW microchannels were visually observed and the boiling heat transfer characteristics were analyzed based on the obtained data. It shows the SW microchannel has a maximum enhancement of 127.7% in local heat transfer coefficient with an acceptable increase of pressure loss compared to the straight one in present work. In SW microchannel, a low degree of superheat can trigger the onset of nucleate boiling. A slow decreasing tendency of local heat transfer coefficient under a high effective heat flux or a high vapor quality was observed. The heat transfer mechanism of flow boiling in SW microchannel was analyzed based on the experimental visualization. Nucleate boiling and thin film evaporation are the dominant modes under different thermal boundary conditions. The flow boiling instability phenomenon in microchannels can be diminished using the wavy structures.
关键词： Boiling heat transfer,Sinusoidal wavy microchannel,Flow instability,Ultrafast laser micromachining
更新于2025-09-19 17:13:59
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[IEEE 2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS) - Vancouver, BC, Canada (2020.1.18-2020.1.22)] 2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS) - A Novel Fabrication Process of Nano-Cavity Coupled Plasmonic Structures for Colormetric Sensing
摘要： This paper develops and validates a universally applicable computational comprehensive concept for solving nonlinear differential equations (NDEs) through a neurocomputing concept based on cellular neural networks (CNNs). High-precision, stability, convergence, and lowest-possible memory requirements are ensured by the CNN processor architecture. A significant challenge solved in this paper is that all these cited computing features are ensured in all system-states (regular or chaotic ones) and in all bifurcation conditions that may be experienced by NDEs. One particular quintessence of this paper is to develop and demonstrate a solver concept that shows and ensures that CNN processors (realized either in hardware or in software) are universal solvers of NDE models. The solving logic or algorithm of given NDEs (possible examples are: Duffing, Mathieu, Van der Pol, Jerk, Chua, R?ssler, Lorenz, Burgers, and the transport equations) through a CNN processor system is provided by a set of templates that are computed by our comprehensive templates calculation technique that we call nonlinear adaptive optimization. This paper is therefore a significant contribution and represents a cutting-edge real-time computational engineering approach, especially while considering the various scientific and engineering applications of this ultrafast, energy-and-memory-efficient, and high-precise three NDE NDE solver concept. For illustration purposes, three NDE models are demonstratively solved, and related CNN templates are derived and used: the periodically excited Duffing equation, the Mathieu equation, and the transport equation.
关键词： Cellular neural networks (CNNs)-based neurocomputing,CNN processor concept as a universal differential equation model solver,CNN-based ultrafast solving of nonlinear differential equations (NDEs),nonlinear adaptive optimization (NAOP)
更新于2025-09-19 17:13:59
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Niobium disulfide as a new saturable absorber for an ultrafast fiber laser
摘要： Group VB transition metal dichalcogenides (TMDCs) are emerging two-dimensional materials and have attracted significant interests in the fields of physics, chemistry, and material sciences. However, there are very few reports about the optical characteristics and ultrafast photonic applications based on group VB TMDCs so far. In this work, we have calculated the niobium disulfide (NbS2) band structure by the density functional theory (DFT), which has revealed that NbS2 is a metallic TMDC. In addition, we have prepared an NbS2-microfiber device and the nonlinear optical characteristics have been investigated. The modulation depth, saturation intensity and non-saturable loss have been measured to be 13.7%, 59.93 MW cm?2 and 17.74%, respectively. Based on the nonlinear optical modulation effect, the Er-doped fiber (EDF) laser works in the soliton mode-locking state with the pump power of 94–413 mW. The pulse duration of 709 fs and the maximum average output power of 23.34 mW have been obtained at the pump power of 413 mW. The slope efficiency is as high as 6.79%. Compared to the recently reported studies based on TMDCs comprehensively, our experimental results are better. These experimental results demonstrate that NbS2 with excellent nonlinear optical properties can be used as a promising candidate to advance the development of ultrafast photonics.
关键词： Niobium disulfide,ultrafast fiber laser,saturable absorber,mode-locking,nonlinear optical properties
更新于2025-09-19 17:13:59
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Photoinduced valence tautomerism of a cobalt-dioxolene complex revealed with femtosecond M-edge XANES
摘要： Cobalt complexes that undergo charge-transfer induced spin-transitions or valence tautomerism from low spin CoIII to high spin (HS) CoII are potential candidates for magneto-optical switches. We use M2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy with 40 fs time resolution to measure the excited-state dynamics of CoIII(Cat-N-SQ)(Cat-N-BQ), where Cat-N-BQ and Cat-N-SQ are the singly and doubly reduced forms of the 2-(2-hydroxy-3,5-di-tert-butylphenyl-imino)-4,6-di-tert-butylcyclohexa-3,5-dienone ligand. The extreme ultraviolet probe pulses, produced using a tabletop high-harmonic generation light source, measure 3p → 3d transitions and are sensitive to the spin and oxidation state of the Co center. Photoexcitation at 525 nm produces a low-spin CoII ligand-to-metal charge transfer state which undergoes intersystem crossing to high-spin CoII in 67 fs. Vibrational cooling from this hot HS CoII state competes on the hundreds-of-fs time scale with back-intersystem crossing to the ground state, with 60% of the population trapped in a cold HS CoII state for 24 ps. Ligand field multiplet simulations accurately reproduce the ground-state spectra and support the excited-state assignments. This work demonstrates the ability of M2,3-edge XANES to measure ultrafast photophysics of molecular Co complexes.
关键词： valence tautomerism,ultrafast spectroscopy,M-edge XANES,Cobalt complexes,high-harmonic generation
更新于2025-09-19 17:13:59
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Nonlinear energy deposition of filamentation with femtosecond Airy laser beams in water
摘要： The nonlinear propagation of femtosecond Airy laser ?laments in water is numerically investigated in this paper. We mainly consider the in?uences of con?nement parameter, pulse duration and beam waist on the deposited energy of ?laments. The values of con?nement parameter are found to have a signi?cant impact on the temporal and spatial dynamics of the pulse. The characteristics of energy deposition also di?er widely for Airy beams with di?erent con?nement parameters. The less the con?nement parameter, the more energy deposited by ?lamentation. However, the relative deposited energy evolves relatively small changes under di?erent con?nement parameters. We also found the longer pulse duration and longer beam waist are bene?cial to the total deposited energy increase.
关键词： self-focusing,Airy beams,energy deposition,Ultrafast nonlinear optics
更新于2025-09-19 17:13:59