Search query: Hot-Electron Transfer from Semiconductor Nanocrystals

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abstract: Hot on the Trail Solar cells essentially operate by absorbing light, which needs to be above a certain energy threshold. The absorbed light then liberates charges within the solar cell to carry electrical current. Unfortunately, the liberated charges behave the same way whether they are excited right at the threshold (e.g. by visible light) or well above it (by ultraviolet light) which leads to any excess energy being dissipated as waste heat. Tisdale et al. (p. 1543) have documented a potential first step toward resolving this inefficiency. Specifically, electrons excited by light absorption in lead selenide nanocrystals were able to migrate to an adjacent titanium dioxide surface without releasing their excess energy to heat. The next step will be to devise a means of harnessing the stored energy in a circuit. Extraction of highly excited electrons formed in a light absorbing material may make solar cells more efficient. In typical semiconductor solar cells, photons with energies above the semiconductor bandgap generate hot charge carriers that quickly cool before all of their energy can be captured, a process that limits device efficiency. Although fabricating the semiconductor in a nanocrystalline morphology can slow this cooling, the transfer of hot carriers to electron and hole acceptors has not yet been thoroughly demonstrated. We used time resolved optical second harmonic generation to observe hot electron transfer from colloidal lead selenide (PbSe) nanocrystals to a titanium dioxide (TiO2) electron acceptor. With appropriate chemical treatment of the nanocrystal surface, this transfer occurred much faster than expected. Moreover, the electric field resulting from sub 50 femtosecond charge separation across the PbSe TiO2 interface excited coherent vibrations of the TiO2 surface atoms, whose motions could be followed in real time.
author_names: William A Tisdale

Kenrick J Williams

Brooke A Timp

David J Norris

Eray S Aydil

X-Y Zhu
title: Hot Electron Transfer from Semiconductor Nanocrystals
venue: Science
year: 2010

abstract: Non noble metal plasmonic materials, e.g. doped semiconductor nanocrystals, compared to their noble metal counterparts, have shown unique advantages, including broadly tunable plasmon frequency (from visible to infrared) and rich surface chemistry. However, the fate and harvesting of hot electrons from these non noble metal plasmons have been much less explored. Here we report plasmon driven hot electron generation and transfer from plasmonic metal oxide nanocrystals to surface adsorbed molecules by ultrafast transient absorption spectroscopy. We show unambiguously that under infrared light excitation, hot electron transfers in ultrafast timescale <50 fs) with an efficiency of 1.4% The excitation wavelength and fluence dependent study indicates that hot electron transfers right after Landau damping before electron thermalization. We revealed the efficiency limiting factors and provided improvement strategies. This study paves the way for designing efficient infrared light absorption and photochemical conversion applications based on non noble metal plasmonic materials. Harvesting of hot electrons in non noble metal plasmonic materials is still little explored. Here the authors investigate plasmon driven hot electron generation in doped metal oxide nanocrystals and the mechanism of transfer to surface adsorbed molecules by ultrafast transient absorption spectroscopy.
author_names: Dongming Zhou

Xufeng Li

Qiaohui Zhou

Haiming Zhu
title: Infrared driven hot electron generation and transfer from non noble metal plasmonic nanocrystals
venue: Nature Communications
year: 2020

abstract: Generation of hot electrons and their utilization in photoinduced chemical processes have been the subjects of intense research in recent years mostly exploring hot electrons in plasmonic metal nanostructures created via decay of optically excited plasmon. Here, we present recent progress made in generation and utilization of a different type of hot electrons produced via biphotonic exciton to hot electron "upconversion" in Mn doped semiconductor nanocrystals. Compared to the plasmonic hot electrons, those produced via biphotonic upconversion in Mn doped semiconductor nanocrystals possess much higher energy, enabling more efficient long range electron transfer across the high energy barrier. They can even be ejected above the vacuum level creating photoelectrons, which can possibly produce solvated electrons. Despite the biphotonic nature of the upconversion process, hot electrons can be generated with weak cw excitation equivalent to the concentrated solar radiation without requiring intense or high energy photons. This perspective reviews recent work elucidating the mechanism of generating energetic hot electrons in Mn doped semiconductor nanocrystals, detection of these hot electrons as photocurrent or photoelectron emission, and their utilization in chemical processes such as photocatalysis. New opportunities that the energetic hot electrons can open by creating solvated electrons, which can be viewed as the longer lived and mobile version of hot electrons more useful for chemical processes, and the challenges in practical utilization of energetic hot electrons are also discussed.
author_names: David Parobek

Tian Qiao

Dong Hee Son
title: Energetic hot electrons from exciton to hot electron upconversion in Mn doped semiconductor nanocrystals.
venue: The Journal of chemical physics
year: 2019

abstract: Semiconductor metal hybrid nanostructures are recognized as great materials due to their high level of light induced charge separation, which has direct relevance in photocatalysis and solar energy conversion. To understand the mechanism of charge separation processes, hybrid CdSe@CdS{Au} nano heterostructures containing Au nanoparticles (NPs) with different sizes were synthesized, and the ultrafast charge transfer dynamics were monitored using femtosecond transient absorption spectroscopy. Steady state optical absorption studies suggest the formation of charge transfer complexes between core shell nanocrystals (NCs) and Au NPs. Steady state and time resolved luminescence spectroscopy suggest electron transfer from the photo excited CdSe@CdS core shell QDs NCs to the Au NPs within the heterostructure. The ultrafast interfacial electron transfer dynamics in the heterostructures were monitored by femtosecond transient absorption spectroscopy. The results revealed that both hot and thermalized electrons are transferred from the core shell QDs to the metal NPs with time constants of 150 and 300 fs, respectively. Hot electron transfer from QDs to Au NPs was found to take place predominantly in the heterostructures depending on the sizes of the metal NPs. The photo degradation of rhodamin B in the presence of the CdSe@CdS{Au} heterostructures under visible light radiation suggests that the hot electrons in the heterostructures play a major role in photocatalytic degradation.
author_names: Jayanta Dana

Partha Maity

Hirendra N Ghosh
title: Hot electron transfer from the semiconductor domain to the metal domain in CdSe@CdS{Au} nano heterostructures.
venue: Nanoscale
year: 2017

abstract: We demonstrate plasmon induced hot electron transfer in Ag CsPbBr3 hybrid nanocrystals. Using transient absorption spectroscopy, we have observed the highly efficient transfer hot electrons from metal Ag to semiconductor CsPbBr3 in a timescale of sub 100 fs.
author_names: Xinyu Huang

Hongbo Li

Chunfeng Zhang

Zhenda Lu

Min Xiao
title: Plasmon Induced Hot Electron Transfer in Ag CsPbBr3 Hybrid Nanocrystals
venue: 2018 Conference on Lasers and Electro Optics (CLEO)
year: 2018

abstract: Exciton delocalizing ligands (EDLs) are of interest to researchers due to their ability to allow charge carriers to spread into the ligand shell of semiconductor nanocrystals (NCs) By increasing charge carrier surface accessibility, EDLs may facilitate the extraction of highly photoexcited carriers from NCs prior to their relaxation to the band edge, a process that can boost the performance of NC based photocatalysts and light harvesting systems. However, hot carrier extraction must compete with carrier cooling, which could be accelerated by the stronger interaction of charge carriers and EDLs. This report describes the influence of the EDL phenyldithiocarbamate (PTC) on the electron and hole cooling rates of CdSe NCs. Using state resolved transient absorption spectroscopy, we find that PTC treatment accelerates hole cooling by a factor of 1.7. However, upon further treatment of these NCs with cadmium(II) acetate, the hole cooling rate reverts to the value measured prior to PTC treatment, yet these NCs m.
author_names: Michael S Azzaro

Mark C Babin

Shannon K Stauffer

Graeme A Henkelman

Sean T Roberts
title: Can Exciton Delocalizing Ligands Facilitate Hot Hole Transfer from Semiconductor Nanocrystals?
year: 2016

abstract: Semiconductor nanocrystals are known to have properties of bulk semiconductors as well as molecules. Two rules that govern molecules are that there is no dual emission (Kasha) and there is no spectrum to the emission quantum yield (Vavilov) We show that the latter rule of molecular spectroscopy is generally violated in semiconductor nanocrystals. Through experiments and theory on CdSe and perovskite nanocrystals, these violations are shown to arise via hot carrier effects. Experiments and simple phenomenology reveal that quantum yield spectra arise because of enhanced hot carrier trapping rates. A semiclassical electron transfer theory rationalizes a microscopic picture of the carrier kinetics. These effects are especially significant when quantifying syntheses of bright emitters such as perovskite nanocrystals. These effects are also a general approach to simple steady state measurements of the action of hot carrier kinetics.
author_names: Baihai Li

Patrick J Brosseau

Dallas P Strandell

Timothy G Mack

Patanjali Kambhampati
title: Photophysical Action Spectra of Emission from Semiconductor Nanocrystals Reveal Violations to the Vavilov Rule Behavior from Hot Carrier Effects
venue: The Journal of Physical Chemistry C
year: 2019

abstract: Hybrid metal/semiconductor nano heterostructures with strong exciton plasmon coupling have been proposed for applications in hot carrier optoelectronic devices. However, the performance of devices based on this concept has been limited by the poor efficiency of plasmon hot electron conversion at the metal/semiconductor interface. Here, we report that the efficiency of interfacial hot excitation transfer can be substantially improved in hybrid metal semiconductor nano heterostructures consisting of perovskite semiconductors. In Ag CsPbBr3 nanocrystals, both the plasmon induced hot electron and the resonant energy transfer processes can occur on a time scale of less than 100 fs with quantum efficiencies of 50 18% and 15 5% respectively. The markedly high efficiency of hot electron transfer observed here can be ascribed to the increased metal/semiconductor coupling compared with those in conventional systems. These findings suggest that hybrid architectures of metal and perovskite semiconductors may be excellent candidates to achieve highly efficient plasmon induced hot carrier devices.Proposed devices exploiting the strong exciton plasmon coupling are limited by the low efficiency of hot carrier generation. Here, Huang et al. study the efficiencies of different plasmon hot electron conversion processes in metal/perovskite semiconductor nanocrystals to address this problem.
author_names: Xinyu Huang

Hongbo Li

Chunfeng Zhang

Shijing Tan

Zhangzhang Chen

Lan Chen

Zhenda Lu

Xiaoyong Wang

Min Xiao
title: Efficient plasmon hot electron conversion in Ag CsPbBr3 hybrid nanocrystals
venue: Nature Communications
year: 2019

abstract: An ideal interface model combining a hematite nanoplate based photoanode with Au nanoparticles (NPs) is proposed for elucidating the specific role of Au NPs in photoelectrochemical performances. The theoretical and experimental results reveal that Au/Fe2O3 nanoplates can lead to an enhanced localized electric field at the metal semiconductor interface upon the formation of surface plasmon resonance and hot electrons, which can be injected into the conduction band of the semiconductor, thus improving the efficiency of the generation and separation of electron hole pairs. As expected, the Au/Fe2O3 nanoplate based photoelectrode possessed a higher carrier density and a photocurrent of 1.7 mA cm 2 and 3.8 mA cm 2 at 1.23 V and 1.5 V vs. RHE, which are nearly 5 times and 30 times larger than that of the Au/Fe2O3 nanocrystals and pristine Fe2O3 nanoplate based photoelectrodes, respectively.
author_names: Fengcai Lei

Huimin Liu

Jing Yu

Zhaofeng Tang

Junfeng Xie

Pin Hao

Guanwei Cui

Bo Tang
title: Promoted water splitting by efficient electron transfer between Au nanoparticles and hematite nanoplates: a theoretical and experimental study.
venue: Physical chemistry chemical physics PCCP
year: 2019

abstract: The excitonics of semiconductor nanocrystals (NC) depend upon temperature in a complex manner due to the interplay between the kinetics of hot exciton relaxation/trapping and the thermodynamics leading to cold exciton recombination. We apply a semiclassical electron transfer model of surface trapping to temperature dependent absorption and emission data to elucidate a microscopic picture of the factors which govern the fate of hot and cold excitons. The linear absorption spectra reveal a unique temperature dependence to the energies of higher excitonic states, while oscillator strength is shown to be temperature invariant. We identify the phonon based origin to the anomalous low temperature peak energy trend in photoluminescence (PL) spectra. PL intensities, PL lifetimes, and absorption spectra are used to demonstrate that variation of quantum yield with temperatures arises from the thermally controlled fraction of NC which emit, rather than from an activated nonradiative pathway common to all NCs. Experi.
author_names: John B Mooney

Michael M Krause

Patanjali Kambhampati
title: Connecting the Dots: The Kinetics and Thermodynamics of Hot, Cold, and Surface Trapped Excitons in Semiconductor Nanocrystals
year: 2014