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Investigating ultrafast carrier dynamics in perovskite solar cells with an extended ??-conjugated polymeric diketopyrrolopyrrole layer for hole transportation
摘要： Here, we show a new diketopyrrole based polymeric hole-transport material (PBDTP-DTDPP, (poly[[2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,20-(4,8-bis(4-ethylhexyl-1-phenyl)-benzo[1,2-b:4,5-b0]dithiophene)bis-thieno[3,2-b]thiophen]-5,50-diyl]])) in perovskite solar cells. The material performance was tested in a solar cell with an optimized configuration, FTO/SnO2/perovskite/PBDTP-DTDPP/Au, and the device showed a power conversion efficiency of 14.78%. The device charge carrier dynamics were investigated using transient absorption spectroscopy. The charge separation and recombination kinetics were determined in a device with PBDTP-DTDPP and the obtained results were compared to a reference device. We find that PBDTP-DTDPP enables similar charge separation time (<4.8 ps) to the spiro-OMeTAD but the amount of nongeminate recombination is different. Specifically, we find that the polymeric PBDTP-DTDPP hole-transport layer (HTL) slows-down the second-order recombination much less than spiro-OMeTAD. This effect is of particular importance in studying the charge transportation in optimized solar cell devices with diketopyrrole based HTL materials.
关键词： perovskite solar cells,transient absorption spectroscopy,PBDTP-DTDPP,charge carrier dynamics,hole-transport material
更新于2025-09-23 15:19:57
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Iron Oxide and Iron Sulfide Films Prepared for Dye-Sensitized Solar Cells
摘要： In this paper, the prospects of iron oxide ?lms and their sul?dation for dye-sensitized solar cells (DSSC) are reviewed. Iron oxide thin ?lms were prepared by hollow cathode plasma jet (HCPJ) sputtering, with an admixture of oxygen in the argon working gas and with an iron nozzle as the sputtering target. The discharge was powered by a constant current source in continuous mode and by a constant voltage source in pulsed mode. Plasma composition was measured by an energy-resolved mass spectrometer. Moreover, secondary electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), absorption and Raman spectra of the ?lms are presented. Strong correlation between the color of the iron oxide ?lm and its phase composition was revealed. Iron oxide ?lms were sul?ded at 350 °C. A relatively clean pyrite phase was obtained from the magnetite, while the marcasite with admixture of the pyrite phase was obtained from the hematite. Low in?uence of sul?dation on the ?lms’ microstructure was demonstrated.
关键词： iron oxide,absorption spectroscopy,hollow cathode plasma jet,dye-sensitized solar cell,iron sul?de
更新于2025-09-23 15:19:57
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Size- and Composition-Dependent Exciton Spin Relaxation in Lead Halide Perovskite Quantum Dots
摘要： The strong spin-orbital coupling in lead halide perovskites allows for facile spin injection for spintronics applications, but on the other hand also limits the lifetime of the injected spins. Full-dimensional confinement of the carriers using quantum dots (QDs) has been envisioned as an effective means to prolong the spin relaxation lifetime and has been explored for II-VI and III-V group QDs. Here we applied this idea to colloidal lead halide perovskite QDs and measured the exciton spin dynamics of QDs of varying sizes and compositions using circularly polarized transient absorption spectroscopy at room temperature. Interestingly, the spin lifetimes of CsPbI3 and CsPbBr3 QDs were prolonged and shortened, respectively, as compared to their bulk counterparts. Both CsPbI3 and CsPbBr3 QDs showed decreasing spin lifetime with decreasing QD size. Possible spin relaxation mechanisms, including those that are unique to these quantum-confined systems, were proposed, with important ramifications for the use of these perovskite QDs in spin-related applications.
关键词： lead halide perovskites,spin-orbital coupling,exciton spin dynamics,circularly polarized transient absorption spectroscopy,quantum dots
更新于2025-09-23 15:19:57
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Pulverized coal combustion application of laser-based temperature sensing system using computed tomography a?? Tunable diode laser absorption spectroscopy (CT-TDLAS)
摘要： The investigation of combustion phenomena in pulverized coal flames is significant for combustion optimization related to energy conservation and emission reduction. Real-time two dimensional (2D) temperature and concentration distributions play an important role for combustion analysis. The non-contact and fast response 2D temperature and concentration distribution measurement method was developed in this study. The method is based on a combination of computed tomography (CT) and tunable diode laser absorption spectroscopy (TDLAS). The accuracy evaluation of developed 32-path CT-TDLAS demonstrated its feasibility of 2D temperature measurement. 32-path CT-TDLAS was applied to CH4 and 5 kg/h coal combustion fields for 2D temperature measurement. The time-series 2D temperature distribution in coal combustion furnace was measured using 32-path CT-TDLAS measurement cell with kHz time resolution. The transient temperature field of combustion flame directly reflects the combustion mode and combustion stability. The measurement results demonstrate its applicability of CT-TDLAS to various types of combustor, especially the combustion fields with coal and ash particles. CT-TDLAS method with kHz response time enables the real-time 2D temperature measurement to be applicable for combustion analysis.
关键词： 2D temperature measurement,Computed tomography (CT),Tunable diode laser absorption spectroscopy (TDLAS),Time-series distribution,Coal combustion
更新于2025-09-23 15:19:57
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Photocarrier relaxation pathway in selenium quantum dots and its application for UV-Vis photodetecting
摘要： Chain-like materials have recently attracted significant attention due to their unique structure and outstanding electro-optical properties. However, the photocarrier dynamics and pathways in these materials that determine the electro-optical performances of the prepared devices have barely been touched. Herein, one typical chain-like materials e quantum dots (Se QDs) were prepared via a facile liquid phase exfoliation approach. The photocarrier dynamics in selenium quantum dots were systematically investigated via ultrafast transient absorption spectroscopy in the ultraviolet-visible regime. Four photocarrier decay pathways with different lifetime times were firstly detected, endues the elucidation and reconstruction of the energy schematic diagram of Se QDs. Thanks to the broadband photo-response and fast recovery time of Se QDs, a photoelectrochemical (PEC)-typed photodetector was proposed for the first time to our knowledge, demonstrating excellent photodetection properties. Considering the feasible fabrication method and clear photocarrier pathways, the excellent photocurrent density and stability of this photodetector undoubtedly guarantee the promising of selenium for advanced photonics devices.
关键词： broadband photo-response,photocarrier dynamics,ultrafast transient absorption spectroscopy,selenium quantum dots,photoelectrochemical photodetector
更新于2025-09-23 15:19:57
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Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study
摘要： Interdot coherent excitonic dynamics in nanometric colloidal CdSe quantum dots (QD) dimers lead to interdot charge migration and energy transfer. We show by electronic quantum dynamical simulations that the interdot coherent response to ultrashort fs laser pulses can be characterized by pump-probe transient absorption spectroscopy in spite of the inevitable inherent size dispersion of colloidal QDs. The latter, leading to a broadening of the excitonic bands, induce accidental resonances that actually increase the efficiency of the interdot coupling. The optical electronic response is computed by solving the time-dependent Schrodinger equation including the interaction with the oscillating electric field of the pulses for an ensemble of dimers that differ by their size. The excitonic Hamiltonian of each dimer is parameterized by the QD size and interdot distance, using an effective mass approximation. Local and charge transfer excitons are included in the dimer basis set. By tailoring the QD size, the excitonic bands can be tuned to overlap and thus favor interdot coupling. Computed pump-probe transient absorption maps averaged over the ensemble show that the coherence of excitons in QD dimers that lead to interdot charge migration can survive size disorder and could be observed in fs pump-probe, four-wave mixing, or covariance spectroscopy.
关键词： coherent electronic dynamics,pump-probe transient absorption spectroscopy,CdSe quantum dots dimers,exciton dynamics,size dispersion effects
更新于2025-09-23 15:19:57
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Spectral Line Shape Analysis Using Hartmann-Tran Profile for Tunable Diode Laser Absorption Spectroscopy of Water Vapor at 1.39a????m
摘要： In this study, spectral line shape analysis was conducted for water vapor absorption at 1.39 μm with a Hartmann-Tran pro?le (HTP), which is capable of being ef?ciently and accurately reduced to (speed dependent) Voigt and (speed dependent) Rautian pro?les. The near-IR absorption lines of water vapor were measured using tunable diode laser absorption spectroscopy (TDLAS). The spectrum ?tting code was home-written based on the Trust region re?ective algorithm and the HTP. Voigt pro?le (VP), Rautian pro?le (RP), speed-dependent VP (SDVP), and speed-dependent Rautian pro?le (SDRP), which were reduced from the HTP, were used as model functions to test the validity of the near-IR absorption lines of water vapor in terms of line shape pro?le. With the SDVP, the standard deviation of the ?tting residuals was at a 10?3 level relative to the most intense peak height in a range of 1.39 μm at 2.5 Torr and room temperature, while the global standard deviation was less than 0.5 × 10?3, thus showing the best result among them. This suggests the need to consider the speed-dependent collision width in the self-broadening of water vapor.
关键词： Tunable diode laser absorption spectroscopy,Hartmann-Tran pro?le,Spectral lineshape analysis,Water vapor
更新于2025-09-23 15:19:57
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Analysis of the Stable Isotope Ratios (18O/16O, 17O/16O and D/H) in Glacier Water by Laser Spectrometry
摘要： A compact isotope ratio sensor based on laser absorption spectroscopy at 2.7 μm was developed for high precision and simultaneous measurements of the D/H, 18O/16O and 17O/16O isotope ratios in glacier water. Measurements of the oxygen and hydrogen isotope ratios in glacier water demonstrate a σ0 precision of 0.3‰ for δ18O, 0.2‰ for δ17O and 0.5‰ for δ2H respectively. The δ values of the working standard glacier water obtained by the calibrated sensor system is basically identical to the IRMS measurement results with a very high calibration accuracy from 0.17‰ to 0.75‰. Preliminary results on the reproducibility measurements display a standard deviation of 0.13‰ for δ18O, 0.13‰ for δ17O and 0.64‰ for δ2H respectively.
关键词： glacier water,laser absorption spectroscopy,isotope ratio
更新于2025-09-23 15:19:57
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Decomposing Electronic and Lattice Contributions in Optical Pump–X-ray Probe Transient Inner-Shell Absorption Spectroscopy of CuO
摘要： Electronic and lattice contributions to picosecond time-resolved X-ray absorption spectra (trXAS) of CuO at the oxygen K-edge are analyzed by comparing trXAS spectra, recorded using excitation wavelengths of 355 nm and 532 nm, to steady-state, temperature-dependent XAS measurements. The trXAS spectra at pump-probe time-delays ≥150 ps are dominated by lattice heating effects. Insight into the temporal evolution of lattice temperature profiles on timescales up to 100’s of nanoseconds after laser excitation are reported, on an absolute temperature scale, with a temporal sensitivity and a spatial selectivity on the order of 10’s of picoseconds and 10’s of nanometers, respectively, effectively establishing an 'ultrafast thermometer'. In particular, for the 532 nm experiment at ~5 mJ/cm2 fluence, both the initial sample temperature and its dynamic evolution are well captured by a one-dimensional thermal energy deposition and diffusion model. The thermal conductivity k = (1.3±0.4) W m–1 K–1 derived from this model is in good agreement with the literature value for CuO powder kpowder = 1.013 W m–1 K–1. For 355 nm excitation, a quantitative analysis of the experiments is hampered by the large temperature gradients within the probed sample volume owing to the small UV penetration depth. The impact of the findings on mitigating or utilizing photoinduced lattice temperature changes in future X-ray free electron laser (XFEL) experiments is discussed.
关键词： X-ray absorption spectroscopy,Ultrafast X-ray spectroscopy,CuO,lattice heating,thermal conductivity
更新于2025-09-19 17:15:36
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Determination of size dependent carrier capture in InGaN/GaN quantum nanowires by femto-second transient absorption spectroscopy: effect of optical phonon, electron-electron scattering and diffusion
摘要： Understanding the ultrafast processes corresponding to carrier capture, thermalization and relaxation is essential to design high-speed optoelectronic devices. Here, we have investigated size dependent carrier capture process in InGaN/GaN 20 nm, 50 nm nanowires and quantum well systems. Femto-second transient absorption spectroscopy reveals that the carrier capture is a two-step process. The carriers are captured in the barrier by polar optical phonon scattering. They further scatter into the active region by electron-electron and polar optical phonon scatterings. The capture is found to slow down for quantum confined structures. A significant number of carriers are found to disappear from the barrier during the diffusion process. All the experimental observations are explained in a simulation framework depicting various scattering mechanisms.
关键词： nanowire,polar optical phonon scattering,electron-electron scattering,transient absorption spectroscopy,carrier capture,electron and phonon dynamics
更新于2025-09-19 17:15:36