1
|
Li Q, Wu K, Zhu H, Yang Y, He S, Lian T. Charge Transfer from Quantum-Confined 0D, 1D, and 2D Nanocrystals. Chem Rev 2024; 124:5695-5763. [PMID: 38629390 PMCID: PMC11082908 DOI: 10.1021/acs.chemrev.3c00742] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Revised: 03/29/2024] [Accepted: 04/02/2024] [Indexed: 05/09/2024]
Abstract
The properties of colloidal quantum-confined semiconductor nanocrystals (NCs), including zero-dimensional (0D) quantum dots, 1D nanorods, 2D nanoplatelets, and their heterostructures, can be tuned through their size, dimensionality, and material composition. In their photovoltaic and photocatalytic applications, a key step is to generate spatially separated and long-lived electrons and holes by interfacial charge transfer. These charge transfer properties have been extensively studied recently, which is the subject of this Review. The Review starts with a summary of the electronic structure and optical properties of 0D-2D nanocrystals, followed by the advances in wave function engineering, a novel way to control the spatial distribution of electrons and holes, through their size, dimension, and composition. It discusses the dependence of NC charge transfer on various parameters and the development of the Auger-assisted charge transfer model. Recent advances in understanding multiple exciton generation, decay, and dissociation are also discussed, with an emphasis on multiple carrier transfer. Finally, the applications of nanocrystal-based systems for photocatalysis are reviewed, focusing on the photodriven charge separation and recombination processes that dictate the function and performance of these materials. The Review ends with a summary and outlook of key remaining challenges and promising future directions in the field.
Collapse
Affiliation(s)
- Qiuyang Li
- Department
of Physics, University of Michigan, 450 Church St, Ann Arbor, Michigan 48109, United States
| | - Kaifeng Wu
- State
Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation
Center of Chemistry for Energy Materials (iChEM), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
- University
of Chinese Academy of Sciences, Beijing 100049, China
| | - Haiming Zhu
- Department
of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
| | - Ye Yang
- The
State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM
(Collaborative Innovation Center of Chemistry for Energy Materials),
College of Chemistry & Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China
| | - Sheng He
- Department
of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Tianquan Lian
- Department
of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| |
Collapse
|
2
|
Liz-Marzán LM, Artzi N, Bals S, Buriak JM, Chan WCW, Chen X, Hersam MC, Kim ID, Millstone JE, Mulvaney P, Parak WJ, Rogach A, Schaak RE. Celebrating a Nobel Prize to the "Discovery of Quantum Dots, an Essential Milestone in Nanoscience". ACS NANO 2023; 17:19474-19475. [PMID: 37847312 DOI: 10.1021/acsnano.3c09671] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2023]
|
3
|
Ruhman S. Solving Quantum-Dot Excitonic Riddles with Absolute Pump-Probe Spectroscopy. J Phys Chem Lett 2021; 12:9336-9343. [PMID: 34549584 DOI: 10.1021/acs.jpclett.1c02408] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Absolute absorption changes in molecular flash photolysis experiments are routinely translated into molar extinction coefficients and oscillator strengths of reactive intermediates. These direct quantum chemical investigation and allow precise concentration readings in later experiments. In this Perspective we show how a similar approach can deliver crucial information for interpreting transient absorption spectra in colloidal semiconductor quantum dots. The intrinsic complexity of such samples stemming from the inhomogeneity of particle size, shape, and surface chemistry poses unique challenges to mechanistic assignment of ultrafast pump-probe measurements. We will describe applications of this approach to elucidate the photophysics of quantum confined nanocrystals made of various semiconducting materials. These case studies demonstrate how, faced with conflicting interpretations, it has pointed in the right direction in assessing single and multiple exciton generation and relaxation, in searches for ultrafast carrier trapping and scavenging, and in tests of band edge level structure and state degeneracies.
Collapse
Affiliation(s)
- Sanford Ruhman
- The Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
| |
Collapse
|
4
|
Ghosh T, Dehnel J, Fabian M, Lifshitz E, Baer R, Ruhman S. Spin Blockades to Relaxation of Hot Multiexcitons in Nanocrystals. J Phys Chem Lett 2019; 10:2341-2348. [PMID: 31002253 DOI: 10.1021/acs.jpclett.9b00992] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The conjecture that, as in bulk semiconductors, hot multiexcitons in nanocrystals cool rapidly to the lowest available energy levels is tested here by recording the effects of a single cold "spectator" exciton on the relaxation dynamics of a subsequently deposited hot counterpart. Results in CdSe/CdS nanodots show that a preexisting cold "spectator exciton" allows only half of the photoexcited electrons to relax directly to the band-edge. The rest are blocked in an excited quantum state due to conflicts in spin orientation. The latter fully relax in this sample only after ∼25 ps as the blocked electrons spins flip, prolonging the temporal window of opportunity for harvesting the retained energy more than 100 fold! Common to all quantum-confined nanocrystals, this process will delay cooling and impact the spectroscopic signatures of hot multiexcitons in all envisioned generation scenarios. How the spin-flipping rate scales with particle size and temperature remains to be determined.
Collapse
Affiliation(s)
- Tufan Ghosh
- The Institute of Chemistry, and the Fritz Haber Center for Molecular Dynamics , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel
| | - Joanna Dehnel
- Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Nancy and Stephen Grand Technion Energy Program , Technion Israel Institute of Technology , Haifa 3200003 , Israel
| | - Marcel Fabian
- The Institute of Chemistry, and the Fritz Haber Center for Molecular Dynamics , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel
| | - Efrat Lifshitz
- Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Nancy and Stephen Grand Technion Energy Program , Technion Israel Institute of Technology , Haifa 3200003 , Israel
| | - Roi Baer
- The Institute of Chemistry, and the Fritz Haber Center for Molecular Dynamics , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel
| | - Sanford Ruhman
- The Institute of Chemistry, and the Fritz Haber Center for Molecular Dynamics , The Hebrew University of Jerusalem , Jerusalem 9190401 , Israel
| |
Collapse
|
5
|
Barak Y, Meir I, Shapiro A, Jang Y, Lifshitz E. Fundamental Properties in Colloidal Quantum Dots. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1801442. [PMID: 29923230 DOI: 10.1002/adma.201801442] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2018] [Revised: 04/22/2018] [Indexed: 06/08/2023]
Abstract
A multidisciplinary approach for the production and characterization of colloidal quantum dots, which show great promise for implementation in modern optoelectronic applications, is described. The approach includes the design and formation of unique core/shell structures with alloy-composed layers between the core and the shell. Such structures eliminate interfacial defects and suppress the Auger process, thus reducing the known fluorescence blinking and endowing the quantum dots with robust chemical and spectral stability. The unique design enables the generation and sustained existence of single and multiple excitons with a defined spin-polarized emission recombination. The studies described herein implement the use of single-dot magneto-optical measurements and optically detected magnetic resonance spectroscopy, for direct identification of interfacial defects and for resolving exciton fine structure. The results are of paramount importance for a fundamental understanding of optical transitions in colloidal quantum dots, with an impact on appropriate materials design for practical applications.
Collapse
Affiliation(s)
- Yahel Barak
- Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Grand Technion Energy Program, Technion, Haifa, 3200003, Israel
| | - Itay Meir
- Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Grand Technion Energy Program, Technion, Haifa, 3200003, Israel
| | - Arthur Shapiro
- Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Grand Technion Energy Program, Technion, Haifa, 3200003, Israel
| | - Youngjin Jang
- Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Grand Technion Energy Program, Technion, Haifa, 3200003, Israel
| | - Efrat Lifshitz
- Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Grand Technion Energy Program, Technion, Haifa, 3200003, Israel
| |
Collapse
|
6
|
Araujo JJ, Brozek CK, Kroupa DM, Gamelin DR. Degenerately n-Doped Colloidal PbSe Quantum Dots: Band Assignments and Electrostatic Effects. NANO LETTERS 2018; 18:3893-3900. [PMID: 29763319 DOI: 10.1021/acs.nanolett.8b01235] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We present a spectroscopic study of colloidal PbSe quantum dots (QDs) that have been photodoped to introduce excess delocalized conduction-band (CB) electrons. High-quality absorption spectra are obtained for these degenerately doped QDs with excess electron concentrations up to ∼1020 cm-3. At the highest doping levels, electrons have completely filled the 1Se orbitals of the CB and partially populated the higher-energy 1Pe orbitals. Spectroscopic changes observed as a function of carrier concentration permit an unambiguous assignment of the second excitonic absorption maximum to 1Ph-1Pe transitions. At intermediate doping levels, a clear absorption feature appears between the first two excitonic maxima that is attributable to parity-forbidden 1Sh,e-1Pe,h excitations, which become observable because of electrostatic symmetry breaking. Redshifts of the main excitonic absorption features with increased carrier concentration are also analyzed. The Coulomb stabilization energies of both the 1Sh-1Se and 1Ph-1Pe excitons in n-doped PbSe QDs are remarkably similar to those observed for multiexcitons with the same electron count. The origins of these redshifts are discussed.
Collapse
Affiliation(s)
- Jose J Araujo
- Department of Chemistry , University of Washington , Seattle , Washington 98195-1700 , United States
| | - Carl K Brozek
- Department of Chemistry , University of Washington , Seattle , Washington 98195-1700 , United States
| | - Daniel M Kroupa
- Department of Chemistry , University of Washington , Seattle , Washington 98195-1700 , United States
| | - Daniel R Gamelin
- Department of Chemistry , University of Washington , Seattle , Washington 98195-1700 , United States
| |
Collapse
|
7
|
Kershaw SV, Rogach AL. Carrier Multiplication Mechanisms and Competing Processes in Colloidal Semiconductor Nanostructures. MATERIALS (BASEL, SWITZERLAND) 2017; 10:E1095. [PMID: 28927007 PMCID: PMC5615749 DOI: 10.3390/ma10091095] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Revised: 09/10/2017] [Accepted: 09/14/2017] [Indexed: 12/14/2022]
Abstract
Quantum confined semiconductor nanoparticles, such as colloidal quantum dots, nanorods and nanoplatelets have broad extended absorption spectra at energies above their bandgaps. This means that they can absorb light at high photon energies leading to the formation of hot excitons with finite excited state lifetimes. During their existence, the hot electron and hole that comprise the exciton may start to cool as they relax to the band edge by phonon mediated or Auger cooling processes or a combination of these. Alongside these cooling processes, there is the possibility that the hot exciton may split into two or more lower energy excitons in what is termed carrier multiplication (CM). The fission of the hot exciton to form lower energy multiexcitons is in direct competition with the cooling processes, with the timescales for multiplication and cooling often overlapping strongly in many materials. Once CM has been achieved, the next challenge is to preserve the multiexcitons long enough to make use of the bonus carriers in the face of another competing process, non-radiative Auger recombination. However, it has been found that Auger recombination and the several possible cooling processes can be manipulated and usefully suppressed or retarded by engineering the nanoparticle shape, size or composition and by the use of heterostructures, along with different choices of surface treatments. This review surveys some of the work that has led to an understanding of the rich carrier dynamics in semiconductor nanoparticles, and that has started to guide materials researchers to nanostructures that can tilt the balance in favour of efficient CM with sustained multiexciton lifetimes.
Collapse
Affiliation(s)
- Stephen V Kershaw
- Department of Materials Science and Engineering and Centre for Functional Photonics (CFP), City University of Hong Kong, Hong Kong S.A.R., China.
| | - Andrey L Rogach
- Department of Materials Science and Engineering and Centre for Functional Photonics (CFP), City University of Hong Kong, Hong Kong S.A.R., China.
| |
Collapse
|
8
|
Spoor FM, Tomić S, Houtepen AJ, Siebbeles LDA. Broadband Cooling Spectra of Hot Electrons and Holes in PbSe Quantum Dots. ACS NANO 2017; 11:6286-6294. [PMID: 28558190 PMCID: PMC5492216 DOI: 10.1021/acsnano.7b02506] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Accepted: 05/30/2017] [Indexed: 05/22/2023]
Abstract
Understanding cooling of hot charge carriers in semiconductor quantum dots (QDs) is of fundamental interest and useful to enhance the performance of QDs in photovoltaics. We study electron and hole cooling dynamics in PbSe QDs up to high energies where carrier multiplication occurs. We characterize distinct cooling steps of hot electrons and holes and build up a broadband cooling spectrum for both charge carriers. Cooling of electrons is slower than of holes. At energies near the band gap we find cooling times between successive electronic energy levels in the order of 0.5 ps. We argue that here the large spacing between successive electronic energy levels requires cooling to occur by energy transfer to vibrational modes of ligand molecules or phonon modes associated with the QD surface. At high excess energy the energy loss rate of electrons is 1-5 eV/ps and exceeds 8 eV/ps for holes. Here charge carrier cooling can be understood in terms of emission of LO phonons with a higher density-of-states in the valence band than the conduction band. The complete mapping of the broadband cooling spectrum for both charge carriers in PbSe QDs is a big step toward understanding and controlling the cooling of hot charge carriers in colloidal QDs.
Collapse
Affiliation(s)
- Frank
C. M. Spoor
- Optoelectronic
Materials Section, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Stanko Tomić
- Joule
Physics Laboratory, School of Computing, Science and Engineering, University of Salford, Manchester M5 4WT, United Kingdom
| | - Arjan J. Houtepen
- Optoelectronic
Materials Section, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Laurens D. A. Siebbeles
- Optoelectronic
Materials Section, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| |
Collapse
|
9
|
Park SD, Baranov D, Ryu J, Cho B, Halder A, Seifert S, Vajda S, Jonas DM. Bandgap Inhomogeneity of a PbSe Quantum Dot Ensemble from Two-Dimensional Spectroscopy and Comparison to Size Inhomogeneity from Electron Microscopy. NANO LETTERS 2017; 17:762-771. [PMID: 28045274 DOI: 10.1021/acs.nanolett.6b03874] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Femtosecond two-dimensional Fourier transform spectroscopy is used to determine the static bandgap inhomogeneity of a colloidal quantum dot ensemble. The excited states of quantum dots absorb light, so their absorptive two-dimensional (2D) spectra will typically have positive and negative peaks. It is shown that the absorption bandgap inhomogeneity is robustly determined by the slope of the nodal line separating positive and negative peaks in the 2D spectrum around the bandgap transition; this nodal line slope is independent of excited state parameters not known from the absorption and emission spectra. The absorption bandgap inhomogeneity is compared to a size and shape distribution determined by electron microscopy. The electron microscopy images are analyzed using new 2D histograms that correlate major and minor image projections to reveal elongated nanocrystals, a conclusion supported by grazing incidence small-angle X-ray scattering and high-resolution transmission electron microscopy. The absorption bandgap inhomogeneity quantitatively agrees with the bandgap variations calculated from the size and shape distribution, placing upper bounds on any surface contributions.
Collapse
Affiliation(s)
- Samuel D Park
- Department of Chemistry and Biochemistry and Renewable and Sustainable Energy Institute, University of Colorado , Boulder, Colorado 80309, United States
| | - Dmitry Baranov
- Department of Chemistry and Biochemistry and Renewable and Sustainable Energy Institute, University of Colorado , Boulder, Colorado 80309, United States
| | - Jisu Ryu
- Department of Chemistry and Biochemistry and Renewable and Sustainable Energy Institute, University of Colorado , Boulder, Colorado 80309, United States
| | - Byungmoon Cho
- Department of Chemistry and Biochemistry and Renewable and Sustainable Energy Institute, University of Colorado , Boulder, Colorado 80309, United States
| | | | | | | | - David M Jonas
- Department of Chemistry and Biochemistry and Renewable and Sustainable Energy Institute, University of Colorado , Boulder, Colorado 80309, United States
| |
Collapse
|
10
|
Yang C, Faust A, Amit Y, Gdor I, Banin U, Ruhman S. Impurity Sub-Band in Heavily Cu-Doped InAs Nanocrystal Quantum Dots Detected by Ultrafast Transient Absorption. J Phys Chem A 2016; 120:3088-97. [DOI: 10.1021/acs.jpca.5b10682] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chunfan Yang
- The Institute of Chemistry and ‡The Institute of Chemistry and the Center
for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Adam Faust
- The Institute of Chemistry and ‡The Institute of Chemistry and the Center
for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Yorai Amit
- The Institute of Chemistry and ‡The Institute of Chemistry and the Center
for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Itay Gdor
- The Institute of Chemistry and ‡The Institute of Chemistry and the Center
for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Uri Banin
- The Institute of Chemistry and ‡The Institute of Chemistry and the Center
for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Sanford Ruhman
- The Institute of Chemistry and ‡The Institute of Chemistry and the Center
for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| |
Collapse
|
11
|
Kumar M, Vezzoli S, Wang Z, Chaudhary V, Ramanujan RV, Gurzadyan GG, Bruno A, Soci C. Hot exciton cooling and multiple exciton generation in PbSe quantum dots. Phys Chem Chem Phys 2016; 18:31107-31114. [DOI: 10.1039/c6cp03790a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
PbSe QDs show high multiple exciton generation (MEG) quantum yield. Here we have investigated the role of theΣtransition in slowing down the hot exciton cooling, which can help MEG to take over phonon relaxation.
Collapse
Affiliation(s)
- Manoj Kumar
- Division of Physics and Applied Physics
- School of Physical and Mathematical Sciences
- Nanyang Technological University
- Singapore
- Singapore
| | - Stefano Vezzoli
- Centre for Disruptive Photonic Technologies
- School of Physical and Mathematical Sciences
- Nanyang Technological University
- Singapore
- Singapore
| | - Zilong Wang
- Division of Physics and Applied Physics
- School of Physical and Mathematical Sciences
- Nanyang Technological University
- Singapore
- Singapore
| | - Varun Chaudhary
- Interdisciplinary Graduate School (IGS)
- Nanyang Technological University
- Singapore
- Singapore
- School of Materials Science and Engineering
| | - Raju V. Ramanujan
- School of Materials Science and Engineering
- Nanyang Technological University
- Singapore 639798
- Singapore
| | - Gagik G. Gurzadyan
- Division of Physics and Applied Physics
- School of Physical and Mathematical Sciences
- Nanyang Technological University
- Singapore
- Singapore
| | - Annalisa Bruno
- Energy Research Institute @ NTU (ERI@N)
- Research Techno Plaza
- Singapore
- Singapore
| | - Cesare Soci
- Division of Physics and Applied Physics
- School of Physical and Mathematical Sciences
- Nanyang Technological University
- Singapore
- Singapore
| |
Collapse
|
12
|
Lifshitz E. Evidence in Support of Exciton to Ligand Vibrational Coupling in Colloidal Quantum Dots. J Phys Chem Lett 2015; 6:4336-4347. [PMID: 26538048 DOI: 10.1021/acs.jpclett.5b01567] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The Perspective focuses on the investigation of an unresolved conflict in semiconductor colloidal quantum dots (CQDs) research, concerning the influence of the immediate surrounding on the optical properties of the materials. Today's advanced synthetic colloidal procedures offer formation of a high-quality inorganic crystallite, capped with various organic/inorganic molecular ligands. The Perspective aims to clarify whether exciton recombination processes in CQDs are influenced by the type of crystallite-ligand bonding and, moreover, whether these excitonic processes experience direct coupling to the ligands' vibrational modes. Most ligands used have redox characteristics whose functional groups are added on to the CQDs' surface via coordination, covalent or ionic bonding. The surface-ligand bonding introduces electronic states either above or below the intraband/interband energy gap, resulting in electronic passivation or in creation of trapping states that affect intraband and interband relaxation processes. Furthermore, crystalline electronic states may have a direct coupling to molecular vibrational states via direct overlap of electronic wave functions or through a long-range energy-transfer process. Also, photoejected carriers resulting from an Auger process or ionization processes may diffuse temporarily onto a ligand site. These scenarios are discussed in the current publication with supporting theoretical and experimental observations.
Collapse
Affiliation(s)
- Efrat Lifshitz
- Schulich Faculty of Chemistry, Russell Berrie Nanotechnology Institute, Solid State Institute, Technion, Israel Institute of Technology , Haifa 32000, Israel
| |
Collapse
|
13
|
Liu J, Kilina SV, Tretiak S, Prezhdo OV. Ligands Slow Down Pure-Dephasing in Semiconductor Quantum Dots. ACS NANO 2015; 9:9106-9116. [PMID: 26284384 DOI: 10.1021/acsnano.5b03255] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
It is well-known experimentally and theoretically that surface ligands provide additional pathways for energy relaxation in colloidal semiconductor quantum dots (QDs). They increase the rate of inelastic charge-phonon scattering and provide trap sites for the charges. We show that, surprisingly, ligands have the opposite effect on elastic electron-phonon scattering. Our simulations demonstrate that elastic scattering slows down in CdSe QDs passivated with ligands compared to that in bare QDs. As a result, the pure-dephasing time is increased, and the homogeneous luminescence line width is decreased in the presence of ligands. The lifetime of quantum superpositions of single and multiple excitons increases as well, providing favorable conditions for multiple excitons generation (MEG). Ligands reduce the pure-dephasing rates by decreasing phonon-induced fluctuations of the electronic energy levels. Surface atoms are most mobile in QDs, and therefore, they contribute greatly to the electronic energy fluctuations. The mobility is reduced by interaction with ligands. A simple analytical model suggests that the differences between the bare and passivated QDs persist for up to 5 nm diameters. Both low-frequency acoustic and high-frequency optical phonons participate in the dephasing processes in bare QDs, while low-frequency acoustic modes dominate in passivated QDs. The theoretical predictions regarding the pure-dephasing time, luminescence line width, and MEG can be verified experimentally by studying QDs with different surface passivation.
Collapse
Affiliation(s)
- Jin Liu
- Department of Chemical Engineering, University of Rochester , Rochester, New York 14627, United States
| | - Svetlana V Kilina
- Department of Chemistry, North Dakota State University , Fargo, North Dakota 58108, United States
| | - Sergei Tretiak
- Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Oleg V Prezhdo
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| |
Collapse
|
14
|
Gdor I, Shapiro A, Yang C, Yanover D, Lifshitz E, Ruhman S. Three-pulse femtosecond spectroscopy of PbSe nanocrystals: 1S bleach nonlinearity and sub-band-edge excited-state absorption assignment. ACS NANO 2015; 9:2138-2147. [PMID: 25629237 DOI: 10.1021/nn5074868] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Above band-edge photoexcitation of PbSe nanocrystals induces strong below band gap absorption as well as a multiphased buildup of bleaching in the 1Se1Sh transition. The amplitudes and kinetics of these features deviate from expectations based on biexciton shifts and state filling, which are the mechanisms usually evoked to explain them. To clarify these discrepancies, the same transitions are investigated here by double-pump-probe spectroscopy. Re-exciting in the below band gap induced absorption characteristic of hot excitons is shown to produce additional excitons with high probability. In addition, pump-probe experiments on a sample saturated with single relaxed excitons prove that the resulting 1Se1Sh bleach is not linear with the number of excitons per nanocrystal. This finding holds for two samples differing significantly in size, demonstrating its generality. Analysis of the results suggests that below band edge induced absorption in hot exciton states is due to excited-state absorption and not to shifted absorption of cold carriers and that 1Se1Sh bleach signals are not an accurate counter of sample excitons when their distribution includes multiexciton states.
Collapse
Affiliation(s)
- Itay Gdor
- Institute of Chemistry, The Hebrew University , Jerusalem 91904, Israel
| | | | | | | | | | | |
Collapse
|
15
|
Zhang X, Zhang Y, Yan L, Wu H, Gao W, Zhao J, Yu WW. PbSe nanocrystal solar cells using bandgap engineering. RSC Adv 2015. [DOI: 10.1039/c5ra10715f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A 12.8% improvement in power conversion efficiency of PbSe nanocrystal-based solar cells was achieved using bandgap engineering.
Collapse
Affiliation(s)
- Xiaoyu Zhang
- State Key Laboratory on Integrated Optoelectronics
- College of Electronic Science and Engineering
- Jilin University
- Changchun 130012
- China
| | - Yu Zhang
- State Key Laboratory on Integrated Optoelectronics
- College of Electronic Science and Engineering
- Jilin University
- Changchun 130012
- China
| | - Long Yan
- State Key Laboratory on Integrated Optoelectronics
- College of Electronic Science and Engineering
- Jilin University
- Changchun 130012
- China
| | - Hua Wu
- State Key Laboratory on Integrated Optoelectronics
- College of Electronic Science and Engineering
- Jilin University
- Changchun 130012
- China
| | - Wenzhu Gao
- State Key Laboratory of Superhard Materials
- College of Physics
- Jilin University
- Changchun 130012
- China
| | - Jun Zhao
- College of Material Science and Engineering
- Qingdao University of Science and Technology
- Qingdao 266042
- China
- Department of Chemistry and Physics
| | - William W. Yu
- State Key Laboratory on Integrated Optoelectronics
- College of Electronic Science and Engineering
- Jilin University
- Changchun 130012
- China
| |
Collapse
|
16
|
Kambhampati P. On the kinetics and thermodynamics of excitons at the surface of semiconductor nanocrystals: Are there surface excitons? Chem Phys 2015. [DOI: 10.1016/j.chemphys.2014.11.008] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
17
|
Tabachnyk M, Ehrler B, Gélinas S, Böhm ML, Walker BJ, Musselman KP, Greenham NC, Friend RH, Rao A. Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals. NATURE MATERIALS 2014; 13:1033-8. [PMID: 25282509 DOI: 10.1038/nmat4093] [Citation(s) in RCA: 142] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 08/27/2014] [Indexed: 05/24/2023]
Abstract
The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.
Collapse
Affiliation(s)
- Maxim Tabachnyk
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Bruno Ehrler
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Simon Gélinas
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Marcus L Böhm
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Brian J Walker
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Kevin P Musselman
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Neil C Greenham
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Richard H Friend
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| | - Akshay Rao
- Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK
| |
Collapse
|
18
|
Yang Y, Lian T. Multiple exciton dissociation and hot electron extraction by ultrafast interfacial electron transfer from PbS QDs. Coord Chem Rev 2014. [DOI: 10.1016/j.ccr.2013.11.013] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
19
|
Trinh MT, Sfeir MY, Choi JJ, Owen JS, Zhu X. A hot electron-hole pair breaks the symmetry of a semiconductor quantum dot. NANO LETTERS 2013; 13:6091-6097. [PMID: 24245919 DOI: 10.1021/nl403368y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The best-understood property of semiconductor quantum dots (QDs) is the size-dependent optical transition energies due to the quantization of charge carriers near the band edges. In contrast, much less is known about the nature of hot electron-hole pairs resulting from optical excitation significantly above the bandgap. Here, we show a transient Stark effect imposed by a hot electron-hole pair on optical transitions in PbSe QDs. The hot electron-hole pair does not behave as an exciton, but more bulk-like as independent carriers, resulting in a transient and varying dipole moment which breaks the symmetry of the QD. As a result, we observe redistribution of optical transition strength to dipole forbidden transitions and the broadening of dipole-allowed transitions during the picosecond lifetime of the hot carriers. The magnitude of symmetry breaking scales with the amount of excess energy of the hot carriers, diminishes as the hot carriers cool down and disappears as the hot electron-hole pair becomes an exciton. Such a transient Stark effect should be of general significance to the understanding of QD photophysics above the bandgap.
Collapse
Affiliation(s)
- M Tuan Trinh
- Department of Chemistry, Columbia University , New York, New York 10027, United States
| | | | | | | | | |
Collapse
|
20
|
Kramer IJ, Sargent EH. The Architecture of Colloidal Quantum Dot Solar Cells: Materials to Devices. Chem Rev 2013; 114:863-82. [DOI: 10.1021/cr400299t] [Citation(s) in RCA: 401] [Impact Index Per Article: 36.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Illan J. Kramer
- Edward S. Rogers Department of Electrical & Computer Engineering, University of Toronto, 10 King’s College Road, Toronto, Ontario M5S 3G4, Canada
| | - Edward H. Sargent
- Edward S. Rogers Department of Electrical & Computer Engineering, University of Toronto, 10 King’s College Road, Toronto, Ontario M5S 3G4, Canada
| |
Collapse
|
21
|
Midgett AG, Luther JM, Stewart JT, Smith DK, Padilha LA, Klimov VI, Nozik AJ, Beard MC. Size and composition dependent multiple exciton generation efficiency in PbS, PbSe, and PbS(x)Se(1-x) alloyed quantum dots. NANO LETTERS 2013; 13:3078-85. [PMID: 23750998 DOI: 10.1021/nl4009748] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Using ultrafast transient absorption and time-resolved photoluminescence spectroscopies, we studied multiple exciton generation (MEG) in quantum dots (QDs) consisting of either PbSe, PbS, or a PbSxSe1-x alloy for various QD diameters with corresponding bandgaps (Eg) ranging from 0.6 to 1 eV. For each QD sample, we determine the MEG efficiency, ηMEG, defined in terms of the electron-hole pair creation energy (εeh) such that ηMEG = Eg/εeh. In previous reports, we found that ηMEG is about two times greater in PbSe QDs compared to bulk PbSe, however, little could be said about the QD-size dependence of MEG. In this study, we find for both PbS and PbSxSe1-x alloyed QDs that ηMEG decreases lineally with increasing QD diameter within the strong confinement regime. When the QD radius is normalized by a material-dependent characteristic radius, defined as the radius at which the electron-hole Coulomb and confinement energies are equivalent, PbSe, PbS, and PbSxSe1-x exhibit similar MEG behaviors. Our results suggest that MEG increases with quantum confinement, and we discuss the interplay between a size-dependent MEG rate versus hot exciton cooling.
Collapse
Affiliation(s)
- Aaron G Midgett
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
| | | | | | | | | | | | | | | |
Collapse
|
22
|
Cihan AF, Hernandez Martinez PL, Kelestemur Y, Mutlugun E, Demir HV. Observation of biexcitons in nanocrystal solids in the presence of photocharging. ACS NANO 2013; 7:4799-4809. [PMID: 23713481 DOI: 10.1021/nn305259g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In nanocrystal quantum dots (NQDs), generating multiexcitons offers an enabling tool for enhancing NQD-based devices. However, the photocharging effect makes understanding multiexciton kinetics in NQD solids fundamentally challenging, which is critically important for solid-state devices. To date, this lack of understanding and the spectral-temporal aspects of the multiexciton recombination still remain unresolved in solid NQD ensembles, which is mainly due to the confusion with recombination of carriers in charged NQDs. In this work, we reveal the spectral-temporal behavior of biexcitons (BXs) in the presence of photocharging using near-unity quantum yield CdSe/CdS NQDs exhibiting substantial suppression of Auger recombination. Here, recombinations of biexcitons and single excitons (Xs) are successfully resolved in the presence of trions in the ensemble measurements of time-correlated single-photon counting at variable excitation intensities and varying emission wavelengths. The spectral behaviors of BXs and Xs are obtained for three NQD samples with different core sizes, revealing the strength tunability of the X-X interaction energy in these NQDs. The extraction of spectrally resolved X, BX, and trion kinetics, which are otherwise spectrally unresolved, is enabled by our approach introducing integrated time-resolved fluorescence. The results are further experimentally verified by cross-checking excitation intensity and exposure time dependencies as well as the temporal evolutions of the photoluminescence spectra, all of which prove to be consistent. The BX and X energies are also confirmed by theoretical calculations. These findings fill an important gap in understanding the spectral dynamics of multiexcitons in such NQD solids under the influence of photocharging effects, paving the way to engineering of multiexciton kinetics in nanocrystal optoelectronics, including NQD-based lasing, photovoltaics, and photodetection.
Collapse
Affiliation(s)
- Ahmet Fatih Cihan
- Department of Electrical and Electronics Engineering, Department of Physics, UNAM Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 Turkey
| | | | | | | | | |
Collapse
|
23
|
Wu K, Liu Z, Zhu H, Lian T. Exciton annihilation and dissociation dynamics in group II-V Cd3P2 quantum dots. J Phys Chem A 2013; 117:6362-72. [PMID: 23611312 DOI: 10.1021/jp402511m] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Semiconductor quantum dots (QDs) have emerged as a new class of light harvesting materials for solar energy conversion due to their unique size-dependent properties. Most recent studies have focused on II-VI group (such as CdX, X = S, Se, and Te) QDs and lead salt (such as PbS, PbSe, and PbTe) QDs. In this paper, we investigate exciton dissociation and annihilation dynamics of Cd3P2 QDs, a low bulk band gap (0.55 eV) II-V group material, to explore their potential application as a light harvesting component for photoreduction systems. For Cd3P2 QDs with 1S exciton band at 650 nm, a long-lived single exciton state with lifetime of 259 ns and a high emission quantum yield of 65% were observed. In Cd3P2 QD-rhodamine B (RhB, an electron acceptor) complexes, excitons in QDs could be dissociated by ultrafast electron transfer to RhB (6.2 ps), and the charge separated state had a long lifetime (31 ns). Although the photoinduced electron transfer rate in QD-RhB complexes decreased with increasing QD size, electron transfer was observed in QDs with 1S exciton bands at wavelength as long as 1050 nm. Compared with CdSe and PbS, Cd3P2 QDs with both more strongly reducing excited states and broader absorption in the visible and near IR region can be readily achieved, making them potential photosensitizers for photodriven water or CO2 reduction reactions.
Collapse
Affiliation(s)
- Kaifeng Wu
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA
| | | | | | | |
Collapse
|
24
|
Baer R, Rabani E. Communication: Biexciton generation rates in CdSe nanorods are length independent. J Chem Phys 2013; 138:051102. [DOI: 10.1063/1.4790600] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
25
|
Zohar G, Baer R, Rabani E. Multiexciton Generation in IV-VI Nanocrystals: The Role of Carrier Effective Mass, Band Mixing, and Phonon Emission. J Phys Chem Lett 2013; 4:317-322. [PMID: 26283441 DOI: 10.1021/jz301892z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We study the role of the effective mass, band mixing, and phonon emission on multiexciton generation in IV-VI nanocrystals. A four-band k · p effective mass model, which allows for an independent variation of these parameters, is adopted to describe the electronic structure of the nanocrystals. Multiexciton generation efficiencies are calculated using a Green's function formalism, providing results that are numerically similar to impact excitation. We find that multiexciton generation efficiencies are maximized when the effective mass of the electron and hole are small and similar. Contact with recent experimental results for multiexciton generation in PbS and PbSe is made.
Collapse
Affiliation(s)
| | - Roi Baer
- ‡Fritz Haber Center for Molecular Dynamics, Institute of Chemistry, Hebrew University, Jerusalem 91904, Israel
| | | |
Collapse
|
26
|
Kershaw SV, Susha AS, Rogach AL. Narrow bandgap colloidal metal chalcogenide quantum dots: synthetic methods, heterostructures, assemblies, electronic and infrared optical properties. Chem Soc Rev 2013; 42:3033-87. [DOI: 10.1039/c2cs35331h] [Citation(s) in RCA: 325] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
|
27
|
|
28
|
Saari JI, Dias EA, Reifsnyder D, Krause MM, Walsh BR, Murray CB, Kambhampati P. Ultrafast electron trapping at the surface of semiconductor nanocrystals: excitonic and biexcitonic processes. J Phys Chem B 2012. [PMID: 23186016 DOI: 10.1021/jp307668g] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Aging of semiconductor nanocrystals (NCs) is well-known to attenuate the spontaneous photoluminescence from the band edge excitonic state by introduction of nonradiative trap states formed at the NC surface. In order to explore charge carrier dynamics dictated by the surface of the NC, femtosecond pump/probe spectroscopic experiments are performed on freshly synthesized and aged CdTe NCs. These experiments reveal fast electron trapping for aged CdTe NCs from the single excitonic state (X). Pump fluence dependence with excitonic state-resolved optical pumping enables directly populating the biexcitonic state (XX), which produces further accelerated electron trapping rates. This increase in electron trapping rate triggers coherent acoustic phonons by virtue of the ultrafast impulsive time scale of the surface trapping process. The observed trapping rates are discussed in terms of electron transfer theory.
Collapse
Affiliation(s)
- Jonathan I Saari
- Department of Chemistry, McGill University, Montreal, QC, H3A 2K6, Canada
| | | | | | | | | | | | | |
Collapse
|
29
|
Yang Y, Rodríguez-Córdoba W, Lian T. Multiple exciton generation and dissociation in PbS quantum dot-electron acceptor complexes. NANO LETTERS 2012; 12:4235-4241. [PMID: 22757981 DOI: 10.1021/nl301847r] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Multiple exciton generation (MEG) in quantum dots (QDs), a process by which one absorbed photon generates multiple electron-hole pairs, has provided exciting possibilities for improving the energy conversion efficiency of photovoltaic and photocatalytic devices. However, implementing MEG in practical devices requires the extraction of multiple charge carriers before exciton-exciton annihilation and the development of materials with improved MEG efficiency. In this report, using PbS QD/methylene blue complexes as a QD/electron acceptor model system, we demonstrate that the presence of electron acceptors does not affect the MEG efficiency of QDs and all generated excitons can be dissociated by electron transfer to the acceptor, achieving MEG and multiple exciton dissociation efficiencies of 112%. We further demonstrate that these efficiencies are not affected by the charging of QDs.
Collapse
Affiliation(s)
- Ye Yang
- Department of Chemistry, Emory University, 1515 Dickey Drive NE, Atlanta, Georgia 30322, USA
| | | | | |
Collapse
|