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Bi-Exciton Dissociation Dynamics in Nano-Hybrid Au-CuInS <sub/>2</sub> Nanocrystals
摘要： Multiexciton harvesting from semiconductor quantum dot has been a new approach for improving the solar cell efficiency in Quantum Dot Sensitized Solar Cells (QDSC). Till date, relation between multiexciton dissociation in metal?semiconductor nanohybrid system and boosting the power conversion efficiency (PCE) of QDSC were never discussed. Herein we report a detailed spectroscopic investigation of biexciton dissociation dynamics in copper indium sulfide (CuInS2, also referred as CIS) and Au-CIS nanohybrid, utilizing both time-resolved PL and ultrafast transient absorption (TA) techniques. Ultrafast transient absorption suggests the formation of bi-exciton in CIS NCs which efficiently dissociates in Au-CIS nanohybrids. Maximum multiexciton dissociation (MED) efficiency is determined to be ~ 80% at higher laser fluency, however it was observed to be 100% at lower laser fluency. Prior to exciton dissociation electrons are captured by Au NP in the nanohybrid from the conduction band of CIS NCs which is energetically higher than Fermi level of Au. Here we demonstrate the proof-of-concept in multi-electron dissociation which may provide a new approach for improving the efficiency in QDSSCs, where we found power conversion efficiency (PCE) of Au-CIS nanohybrids up to 2.49% as compared to ~1.06% ~for pure CIS NCs in similar condition. This finding can be an efficient approach towards the design and development of efficient solar cell and optoelectronic devices using the principles of multiexciton generation and extracting multiexcitons in metal-semiconductor nanohybrid system.
关键词： copper indium sulfide,biexciton dissociation dynamics,Quantum Dot Sensitized Solar Cells,power conversion efficiency,ultrafast transient absorption,Multiexciton harvesting,Au-CIS nanohybrid
更新于2025-09-23 15:21:21
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[IEEE 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Zatoka, Ukraine (2018.9.9-2018.9.14)] 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Time-Resolved Photoluminescence of CdSe/CdS/CdZnS Quantum Dots
摘要： We demonstrate that in the study of time-resolved photoluminescence the signatures of biexcitons in QDs can manifest themselves even when the system is excited by long laser pulses with their duration of the order of several tens of picoseconds. To describe the results of our measurements we propose an elegant theoretical model. It is based on the introduction of auxiliary sources in the rate equations. The parameters of the sources are determined by fitting the analytical solution of these equations that describes the full emission of the system to the experimental results obtained. Having found the parameters of the auxiliary sources we can determine the temporal dependences of the radiation from excitons and biexcitons separately. We find the spectral positions of the exciton and biexciton emission bands, their widths, and the biexciton binding energy.
关键词： quantum dots,photoluminescence,exciton,rate equations,binding energy,biexciton
更新于2025-09-23 15:19:57
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The binding energy of biexcitons in alloy ZnxCd1a??xS quantum dots detected by femtosecond laser spectroscopy
摘要： Biexcitons localized at ZnxCd1?xS quantum dots (x = 0.37 or 0.45) with a diameter of ~ 45?? synthesized by two different methods were studied by femtosecond laser spectroscopy. The spectral features of ultrafast transient absorption spectra at the short-time delay of 70?fs are associated with the three lowest energy transitions of quantum dots. The shapes of the transient absorption bands were modeled by fitting to linear absorption. The spectral positions of the absorption components of the excited state in the transient spectra take into account the energy of the biexciton coupling. By fitting the experimental transient absorption spectra of ZnxCd1?xS QDs, the binding energies of biexcitons were determined. The biexciton binding energies vary from 16.6 to 37?meV depending on the biexciton transition excited at the ZnxCd1?xS quantum dot.
关键词： ZnxCd1?xS,Biexciton,Quantum dots,Femtosecond spectroscopy
更新于2025-09-23 15:19:57
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Biexciton Auger recombination in mono-dispersed, quantum-confined CsPbBr3 perovskite nanocrystals obeys universal volume-scaling
摘要： Auger recombination has been a long-standing obstacle to many prospective applications of colloidal quantum dots (QDs) ranging from lasing, light-emitting diodes to bio-labeling. As such, understanding the physical underpinnings and scaling laws for Auger recombination is essential to these applications. Previous studies of biexciton Auger recombination in various QDs established a universal scaling of biexciton lifetime (τXX) with QD volume (V ): τXX = γV. However, recent measurements on perovskite nanocrystals (NCs), an emerging class of enablers for light harvesting and emitting applications, showed significant deviations from this universal scaling law, likely because the measured NCs are weakly-confined and also have relatively broad size-distributions. Here we study biexciton Auger recombination in mono-dispersed (size distributions within 1.7%–9.0%), quantum-confined CsPbBr3 NCs (with confinement energy up to 410 meV) synthesized using a latest approach based on thermodynamic equilibrium control. Our measurements clearly reproduce the volume-scaling of τXX in confined CsPbBr3 QDs. However, the scaling factor γ (0.085 ± 0.001 ps/nm3) is one order of magnitude lower than that reported for CdSe and PbSe QDs (1.00 ± 0.05 ps/nm3), suggesting unique mechanisms enhancing Auger recombination rate in perovskite NCs.
关键词： biexciton,Auger recombination,perovskite nanocrystals,ultrafast spectroscopy,volume-scaling
更新于2025-09-23 15:19:57
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The electronic and optical properties of an exciton, biexciton and charged excitons in CdSe/CdTe-based multi-shell type-II quantum dot nanocrystals
摘要： It has been recently reported that multi-shell type-II quantum dot nanocrystals (QDNCs) have higher quantum yields. Besides these higher quantum yields of multi-shell type-II QDNCs, additional second layer has been a critical influence on the formation mechanisms of the excitonic structures. Understanding of bound and unbound cases of the excitonic structures in multi-shell type-II QDNCs gives some important information for applications. In this study, we have investigated the electronic and optical properties of a single exciton (X), biexciton (XX), and positively and negatively charged excitons ( ??+ and ??? ) in CdSe/CdTe-based multi-shell type-II QDNCs. In the study, three different structure compositions, i.e., CdSe/CdTe, CdSe/CdTe/CdS, and CdSe/CdTe/ZnTe, have been considered. We have observed that CdS and ZnTe materials have drastically changed the electronic and optical properties of the bare CdSe/CdTe type-II QDNCs.
关键词： Exciton,CdS,Biexciton,CdSe/CdTe,Charged excitons,ZnTe,Quantum dot nanocrystals,Type-II
更新于2025-09-12 10:27:22
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Excitonic complexes in MOCVD-grown InGaAs/GaAs quantum dots emitting at telecom wavelengths
摘要： Hereby, we present a comprehensive experimental and theoretical study of the electronic structure and optical properties of excitonic complexes in strain-engineered InGaAs/GaAs quantum dots (QDs) grown by metalorganic chemical vapor deposition and emitting at the 1.3-μm telecommunication window. Single QD properties have been determined experimentally for a number of nanostructures by means of excitation-power-dependent and polarization-resolved microphotoluminescence and further compared with the results of confined states calculations employing the eight-band k·p theory combined with the configuration interaction method. The origin of excitonic complexes has been exemplarily confirmed based on magneto-optical and correlation spectroscopy study. Understanding the influence of structural parameters and compositions (of QDs themselves as well as in the neighboring strain-reducing layer) allows identification of which of them are crucial to control the emission wavelength to achieve the telecommunication spectral range or to affect binding energies of the fundamental excitonic complexes. The obtained results provide deeper knowledge of control and limitations of the investigated structures in terms of good spectral isolation of individual optical transitions and spatial confinement, which are crucial in view of QD applications in single-photon sources of high purity at telecom wavelengths.
关键词： strain-reducing layer,biexciton,quantum dots,single-photon sources,exciton,telecommunication wavelengths
更新于2025-09-12 10:27:22
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Excitonic complexes in anisotropic atomically thin two-dimensional materials: Black phosphorus and
摘要： The effect of anisotropy in the energy spectrum on the binding energy and structural properties of excitons, trions, and biexcitons is investigated. To this end we employ the stochastic variational method with a correlated Gaussian basis. We present results for the binding energy of different excitonic complexes in black phosphorus (bP) and TiS3 and compare them with recent results in the literature when available, for which we find good agreement. The binding energies of excitonic complexes in bP are larger than those in TiS3. We calculate the different average interparticle distances in bP and TiS3 and show that excitonic complexes in bP are strongly anisotropic whereas in TiS3 they are almost isotropic, even though the constituent particles have an anisotropic energy spectrum. This is also confirmed by the correlation functions.
关键词： biexciton,TiS3,binding energy,black phosphorus,trion,anisotropy,stochastic variational method,exciton
更新于2025-09-09 09:28:46