1
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Rudayni F, Rijal K, Fuller N, Chan WL. Enthalpy-uphill exciton dissociation in organic/2D heterostructures promotes free carrier generation. MATERIALS HORIZONS 2024; 11:813-821. [PMID: 38018228 DOI: 10.1039/d3mh01522j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2023]
Abstract
Despite the large binding energy of charge transfer (CT) excitons in type-II organic/2D heterostructures, it has been demonstrated that free carriers can be generated from CT excitons with a long lifetime. Using a model fluorinated zine phthalocyanine (F8ZnPc)/monolayer-WS2 interface, we find that CT excitons can dissociate spontaneously into free carriers despite it being an enthalpy-uphill process. Specifically, it is observed that CT excitons can gain an energy of 250 meV in 50 ps and dissociate into free carriers without any applied electric field. This observation is surprising because excited electrons typically lose energy to the environment and relax to lower energy states. We hypothesize that this abnormal enthalpy-uphill CT exciton dissociation process is driven by entropy gain. Kinetically, the entropic driving force can also reduce the rate for the reverse process - the conversion of free electron-hole pairs back to CT excitons. Hence, this mechanism can potentially explain the very long carrier lifetime observed in organic/2D heterostructures.
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Affiliation(s)
- Fatimah Rudayni
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, US.
- Department of Physics, Jazan University, Jazan 45142, Saudi Arabia
| | - Kushal Rijal
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, US.
| | - Neno Fuller
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, US.
| | - Wai-Lun Chan
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, US.
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2
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Lim JWM, Guo Y, Feng M, Cai R, Sum TC. Making and Breaking of Exciton Cooling Bottlenecks in Halide Perovskite Nanocrystals. J Am Chem Soc 2024; 146:437-449. [PMID: 38158611 DOI: 10.1021/jacs.3c09761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
Harnessing quantum confinement (QC) effects in semiconductors to retard hot carrier cooling (HCC) is an attractive approach for enabling efficient hot carrier extraction to overcome the Shockley-Queisser limit. However, there is a debate about whether halide perovskite nanocrystals (PNCs) can effectively exploit these effects. To address this, we utilized pump-probe and multipulse pump-push-probe spectroscopy to investigate HCC behavior in PNCs of varying sizes and cation compositions. Our results validate the presence of an intrinsic phonon bottleneck with clear manifestations of QC effects in small CsPbBr3 PNCs exhibiting slower HCC rates compared to those of larger PNCs. However, the replacement of inorganic Cs+ with organic cations suppresses this intrinsic bottleneck. Furthermore, PNCs exhibit distinct size-dependent HCC behavior in response to changes in the cold carrier densities. We attribute this to the enhanced exciton-exciton interactions in strongly confined PNCs that facilitate Auger heating. Importantly, our findings dispel the existing controversy and provide valuable insights into design principles for engineering QC effects in PNC hot carrier applications.
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Affiliation(s)
- Jia Wei Melvin Lim
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
| | - Yuanyuan Guo
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
| | - Minjun Feng
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
| | - Rui Cai
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
| | - Tze Chien Sum
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
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3
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Yue L, Li J, Qi Y, Chen J, Wang X, Cao J. Auger Recombination and Carrier-Lattice Thermalization in Semiconductor Quantum Dots under Intense Excitation. NANO LETTERS 2023; 23:2578-2585. [PMID: 36972411 DOI: 10.1021/acs.nanolett.2c04804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
A thorough understanding of the photocarrier relaxation dynamics in semiconductor quantum dots (QDs) is essential to optimize their device performance. However, resolving hot carrier kinetics under high excitation conditions with multiple excitons per dot is challenging because it convolutes several ultrafast processes, including Auger recombination, carrier-phonon scattering, and phonon thermalization. Here, we report a systematic study of the lattice dynamics induced by intense photoexcitation in PbSe QDs. By probing the dynamics from the lattice perspective using ultrafast electron diffraction together with modeling the correlated processes collectively, we can differentiate their roles in photocarrier relaxation. The results reveal that the observed lattice heating time scale is longer than that of carrier intraband relaxation obtained previously using transient optical spectroscopy. Moreover, we find that Auger recombination efficiently annihilates excitons and speeds up lattice heating. This work can be readily extended to other semiconductor QDs systems with varying dot sizes.
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Affiliation(s)
- Luye Yue
- Center for Ultrafast Science and Technology, Key Laboratory for Laser Plasmas (Ministry of Education) and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Jingjun Li
- Center for Ultrafast Science and Technology, Key Laboratory for Laser Plasmas (Ministry of Education) and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Yingpeng Qi
- Center for Ultrafast Science and Technology, Key Laboratory for Laser Plasmas (Ministry of Education) and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Jie Chen
- Center for Ultrafast Science and Technology, Key Laboratory for Laser Plasmas (Ministry of Education) and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Xuan Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Jianming Cao
- Center for Ultrafast Science and Technology, Key Laboratory for Laser Plasmas (Ministry of Education) and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
- Physics Department and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
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4
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Ballabio M, Cánovas E. Electron Transfer at Quantum Dot–Metal Oxide Interfaces for Solar Energy Conversion. ACS NANOSCIENCE AU 2022; 2:367-395. [PMID: 36281255 PMCID: PMC9585894 DOI: 10.1021/acsnanoscienceau.2c00015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Electron transfer
at a donor–acceptor quantum dot–metal
oxide interface is a process fundamentally relevant to solar energy
conversion architectures as, e.g., sensitized solar cells and solar
fuels schemes. As kinetic competition at these technologically relevant
interfaces largely determines device performance, this Review surveys
several aspects linking electron transfer dynamics and device efficiency;
this correlation is done for systems aiming for efficiencies up to
and above the ∼33% efficiency limit set by Shockley and Queisser
for single gap devices. Furthermore, we critically comment on common
pitfalls associated with the interpretation of kinetic data obtained
from current methodologies and experimental approaches, and finally,
we highlight works that, to our judgment, have contributed to a better
understanding of the fundamentals governing electron transfer at quantum
dot–metal oxide interfaces.
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Affiliation(s)
- Marco Ballabio
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia), 28049 Madrid, Spain
| | - Enrique Cánovas
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia), 28049 Madrid, Spain
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5
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Chi Z, Zhang X, Wen X, Han J, Wei Z, Du L, Lai J, Wang X, Zhang G, Zhao Q, Chen H, Ajayan PM, Weng YX. Determining Quasiparticle Bandgap of Two-Dimensional Transition Metal Dichalcogenides by Observation of Hot Carrier Relaxation Dynamics. J Phys Chem Lett 2021; 12:585-591. [PMID: 33382603 DOI: 10.1021/acs.jpclett.0c03414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Using excitation-energy-scanning ultrafast infrared microspectroscopy, the excess energy-dependent hot carrier relaxation dynamics in atomically thin two-dimensional transition metal dichalcogenides (2D TMDs) after femtosecond photoexcitation was directly monitored. A good linear relationship between the carrier relaxation time and the excitation wavelength is observed for all measured monolayer (ML) and bilayer (BL) TMD samples, which allows us to determine their quasiparticle bandgaps as well as corresponding exciton binding energies. A carrier-optical-phonon scattering-mediated cascading-relaxation model is proposed, which can perfectly describe all the measured dynamics. As a consequence, the quasiparticle bandgaps of ML MoSe2, ML MoS2, BL MoSe2, and BL WSe2 are determined to be 2.07, 2.11, 1.67, and 1.81 eV, respectively. Our work reveals a general picture for the hot carrier relaxation dynamics in atomically thin TMDs and offers an effective experimental approach in probing the bandgaps of TMDs under ambient conditions.
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Affiliation(s)
- Zhen Chi
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Center for Quantum Technology Research, School of Physics, Beijing Institute of Technology, Beijing 100081, China
- Institute of Photo-biophysics, School of Physics and Electronics, Henan University, Kaifeng 475004, China
| | - Xiang Zhang
- Department of Materials Science and NanoEngineering, Rice University, 6100 Main Street, Houston, Texas 77005-1892, United States
| | - Xiewen Wen
- Department of Materials Science and NanoEngineering, Rice University, 6100 Main Street, Houston, Texas 77005-1892, United States
| | - Junfeng Han
- Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems, and School of Physics, Beijing Institute of Technology, Beijing 100081, China
- Micronano Center, Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing 100081, China
| | - Zheng Wei
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Luojun Du
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Jiawei Lai
- Department of Materials Science and NanoEngineering, Rice University, 6100 Main Street, Houston, Texas 77005-1892, United States
| | - Xiangzhuo Wang
- Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems, and School of Physics, Beijing Institute of Technology, Beijing 100081, China
- Micronano Center, Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing 100081, China
| | - Guangyu Zhang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Qing Zhao
- Center for Quantum Technology Research, School of Physics, Beijing Institute of Technology, Beijing 100081, China
| | - Hailong Chen
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Pulickel M Ajayan
- Department of Materials Science and NanoEngineering, Rice University, 6100 Main Street, Houston, Texas 77005-1892, United States
| | - Yu-Xiang Weng
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
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6
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Spoor FCM, Grimaldi G, Kinge S, Houtepen AJ, Siebbeles LDA. Model To Determine a Distinct Rate Constant for Carrier Multiplication from Experiments. ACS APPLIED ENERGY MATERIALS 2019; 2:721-728. [PMID: 30714025 PMCID: PMC6354726 DOI: 10.1021/acsaem.8b01779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Accepted: 12/13/2018] [Indexed: 05/15/2023]
Abstract
Carrier multiplication (CM) is the process in which multiple electron-hole pairs are created upon absorption of a single photon in a semiconductor. CM by an initially hot charge carrier occurs in competition with cooling by phonon emission, with the respective rates determining the CM efficiency. Up until now, CM rates have only been calculated theoretically. We show for the first time how to extract a distinct CM rate constant from experimental data of the relaxation time of hot charge carriers and the yield of CM. We illustrate this method for PbSe quantum dots. Additionally, we provide a simplified method using an estimated energy loss rate to estimate the CM rate constant just above the onset of CM, when detailed experimental data of the relaxation time is missing.
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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
| | - Gianluca Grimaldi
- Optoelectronic Materials
Section, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Sachin Kinge
- Toyota Motor Europe, Materials Research
& Development, Hoge
Wei 33, B-1930, Zaventem, Belgium
| | - Arjan J. Houtepen
- Optoelectronic Materials
Section, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
- E-mail:
| | - Laurens D. A. Siebbeles
- Optoelectronic Materials
Section, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
- E-mail:
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7
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Wang HI, Infante I, Brinck ST, Cánovas E, Bonn M. Efficient Hot Electron Transfer in Quantum Dot-Sensitized Mesoporous Oxides at Room Temperature. NANO LETTERS 2018; 18:5111-5115. [PMID: 30039708 DOI: 10.1021/acs.nanolett.8b01981] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Hot carrier cooling processes represent one of the major efficiency losses in solar energy conversion. Losses associated with cooling can in principle be circumvented if hot carrier extraction toward selective contacts is faster than hot carrier cooling in the absorber (in so-called hot carrier solar cells). Previous work has demonstrated the possibility of hot electron extraction in quantum dot (QD)-sensitized systems, in particular, at low temperatures. Here we demonstrate a room-temperature hot electron transfer (HET) with up to unity quantum efficiency in strongly coupled PbS quantum dot-sensitized mesoporous SnO2. We show that the HET efficiency is determined by a kinetic competition between HET rate ( KHET) and the thermalization rate ( KTH) in the dots. KHET can be modulated by changing the excitation photon energy; KTH can be modified through the lattice temperature. DFT calculations demonstrate that the HET rate and efficiency are primarily determined by the density of the state (DoS) of QD and oxide. Our results provide not only a new way to achieve efficient hot electron transfer at room temperature but also new insights on the mechanism of HET and the means to control it.
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Affiliation(s)
- Hai I Wang
- Max Planck Institute for Polymer Research , Ackermannweg 10 , Mainz 55128 , Germany
- Graduate School of Material Science in Mainz , University of Mainz , Staudingerweg 9 , Mainz 55128 , Germany
| | - Ivan Infante
- Department of Theoretical Chemistry, Faculty of Sciences , Vrije Universiteit Amsterdam , De Boelelaan 1083 , HV Amsterdam 1081 , The Netherlands
| | - Stephanie Ten Brinck
- Department of Theoretical Chemistry, Faculty of Sciences , Vrije Universiteit Amsterdam , De Boelelaan 1083 , HV Amsterdam 1081 , The Netherlands
| | - Enrique Cánovas
- Max Planck Institute for Polymer Research , Ackermannweg 10 , Mainz 55128 , Germany
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) , Faraday 9 , Madrid 28049 , Spain
| | - Mischa Bonn
- Max Planck Institute for Polymer Research , Ackermannweg 10 , Mainz 55128 , Germany
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8
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Spoor FM, Grimaldi G, Delerue C, Evers WH, Crisp RW, Geiregat P, Hens Z, Houtepen AJ, Siebbeles LDA. Asymmetric Optical Transitions Determine the Onset of Carrier Multiplication in Lead Chalcogenide Quantum Confined and Bulk Crystals. ACS NANO 2018; 12:4796-4802. [PMID: 29664600 PMCID: PMC5968429 DOI: 10.1021/acsnano.8b01530] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 04/17/2018] [Indexed: 05/27/2023]
Abstract
Carrier multiplication is a process in which one absorbed photon excites two or more electrons. This is of great promise to increase the efficiency of photovoltaic devices. Until now, the factors that determine the onset energy of carrier multiplication have not been convincingly explained. We show experimentally that the onset of carrier multiplication in lead chalcogenide quantum confined and bulk crystals is due to asymmetric optical transitions. In such transitions most of the photon energy in excess of the band gap is given to either the hole or the electron. The results are confirmed and explained by theoretical tight-binding calculations of the competition between impact ionization and carrier cooling. These results are a large step forward in understanding carrier multiplication and allow for a screening of materials with an onset of carrier multiplication close to twice the band gap energy. Such materials are of great interest for development of highly efficient photovoltaic devices.
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Affiliation(s)
- Frank
C. M. Spoor
- Chemical
Engineering Department, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Gianluca Grimaldi
- Chemical
Engineering Department, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | | | - Wiel H. Evers
- Chemical
Engineering Department, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Ryan W. Crisp
- Chemical
Engineering Department, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Pieter Geiregat
- Physics
and Chemistry of Nanostructures, Ghent University, 9000 Ghent, Belgium
| | - Zeger Hens
- Physics
and Chemistry of Nanostructures, Ghent University, 9000 Ghent, Belgium
| | - Arjan J. Houtepen
- Chemical
Engineering Department, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Laurens D. A. Siebbeles
- Chemical
Engineering Department, Delft University
of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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9
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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.
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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.
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10
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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.
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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
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11
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Cánovas E, Wang H, Karakus M, Bonn M. Hot electron transfer from PbSe quantum dots molecularly bridged to mesoporous tin and titanium oxide films. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2015.11.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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12
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Abstract
Understanding photoinduced charge transfer from nanomaterials is essential to the many applications of these materials. This review summarizes recent progress in understanding charge transfer from quantum dots (QDs), an ideal model system for investigating fundamental charge transfer properties of low-dimensional quantum-confined nanomaterials. We first discuss charge transfer from QDs to weakly coupled acceptors within the framework of Marcus nonadiabatic electron transfer (ET) theory, focusing on the dependence of ET rates on reorganization energy, electronic coupling, and driving force. Because of the strong electron-hole interaction, we show that ET from QDs should be described by the Auger-assisted ET model, which is significantly different from ET between molecules or from bulk semiconductor electrodes. For strongly quantum-confined QDs on semiconductor surfaces, the coupling can fall within the strong coupling limit, in which case the donor-acceptor interaction and ET properties can be described by the Newns-Anderson model of chemisorption. We also briefly discuss recent progress in controlling charge transfer properties in quantum-confined nanoheterostructures through wavefunction engineering and multiple exciton dissociation. Finally, we identify a few key areas for further research.
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Affiliation(s)
- Haiming Zhu
- Department of Chemistry, Emory University, Atlanta, Georgia 30322;
| | - Ye Yang
- Department of Chemistry, Emory University, Atlanta, Georgia 30322;
| | - Kaifeng Wu
- Department of Chemistry, Emory University, Atlanta, Georgia 30322;
| | - Tianquan Lian
- Department of Chemistry, Emory University, Atlanta, Georgia 30322;
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13
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Spoor FCM, Kunneman LT, Evers WH, Renaud N, Grozema FC, Houtepen AJ, Siebbeles LDA. Hole Cooling Is Much Faster than Electron Cooling in PbSe Quantum Dots. ACS NANO 2016; 10:695-703. [PMID: 26654878 DOI: 10.1021/acsnano.5b05731] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
In semiconductor quantum dots (QDs), charge carrier cooling is in direct competition with processes such as carrier multiplication or hot charge extraction that may improve the light conversion efficiency of photovoltaic devices. Understanding charge carrier cooling is therefore of great interest. We investigate high-energy optical transitions in PbSe QDs using hyperspectral transient absorption spectroscopy. We observe bleaching of optical transitions involving higher valence and conduction bands upon band edge excitation. The kinetics of rise of the bleach of these transitions after a pump laser pulse allow us to monitor, for the first time, cooling of hot electrons and hot holes separately. Our results show that holes cool significantly faster than electrons in PbSe QDs. This is in contrast to the common assumption that electrons and holes behave similarly in Pb chalcogenide QDs and has important implications for the utilization of hot charge carriers in photovoltaic devices.
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Affiliation(s)
- Frank C M Spoor
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Lucas T Kunneman
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Wiel H Evers
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology , Lorentzweg 1, 2628 CJ Delft, The Netherlands
| | - Nicolas Renaud
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Ferdinand C Grozema
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Arjan J Houtepen
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Laurens D A Siebbeles
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
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14
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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.
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Affiliation(s)
- Efrat Lifshitz
- Schulich Faculty of Chemistry, Russell Berrie Nanotechnology Institute, Solid State Institute, Technion, Israel Institute of Technology , Haifa 32000, Israel
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15
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Ellis JL, Hickstein DD, Schnitzenbaumer KJ, Wilker MB, Palm BB, Jimenez JL, Dukovic G, Kapteyn HC, Murnane MM, Xiong W. Solvents effects on charge transfer from quantum dots. J Am Chem Soc 2015; 137:3759-62. [PMID: 25751367 DOI: 10.1021/jacs.5b00463] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
To predict and understand the performance of nanodevices in different environments, the influence of the solvent must be explicitly understood. In this Communication, this important but largely unexplored question is addressed through a comparison of quantum dot charge transfer processes occurring in both liquid phase and in vacuum. By comparing solution phase transient absorption spectroscopy and gas-phase photoelectron spectroscopy, we show that hexane, a common nonpolar solvent for quantum dots, has negligible influence on charge transfer dynamics. Our experimental results, supported by insights from theory, indicate that the reorganization energy of nonpolar solvents plays a minimal role in the energy landscape of charge transfer in quantum dot devices. Thus, this study demonstrates that measurements conducted in nonpolar solvents can indeed provide insight into nanodevice performance in a wide variety of environments.
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Affiliation(s)
- Jennifer L Ellis
- †Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, United States
| | - Daniel D Hickstein
- †Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, United States
| | - Kyle J Schnitzenbaumer
- ‡Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Molly B Wilker
- ‡Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Brett B Palm
- §Department of Chemistry and Biochemistry and CIRES, University of Colorado, Boulder, Colorado 80309, United States
| | - Jose L Jimenez
- §Department of Chemistry and Biochemistry and CIRES, University of Colorado, Boulder, Colorado 80309, United States
| | - Gordana Dukovic
- ‡Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Henry C Kapteyn
- †Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, United States
| | - Margaret M Murnane
- †Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, United States
| | - Wei Xiong
- †Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, United States
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16
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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]
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17
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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.
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Affiliation(s)
- M Tuan Trinh
- Department of Chemistry, Columbia University , New York, New York 10027, United States
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18
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Choi Y, Sim S, Lim SC, Lee YH, Choi H. Ultrafast biexciton spectroscopy in semiconductor quantum dots: evidence for early emergence of multiple-exciton generation. Sci Rep 2013; 3:3206. [PMID: 24220495 PMCID: PMC3826098 DOI: 10.1038/srep03206] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 10/25/2013] [Indexed: 12/03/2022] Open
Abstract
Understanding multiple-exciton generation (MEG) in quantum dots (QDs) requires in-depth measurements of transient exciton dynamics. Because MEG typically faces competing ultrafast energy-loss intra-band relaxation, it is of central importance to investigate the emerging time-scale of the MEG kinetics. Here, we present ultrafast spectroscopic measurements of the MEG in PbS QDs via probing the ground-state biexciton transients. Specifically, we directly compare the biexciton spectra with the single-exciton ones before and after the intra-band relaxation. Early emergence of MEG is evidenced by observing transient Stark shift and quasi-instantaneous linewidth broadening, both of which take place before the intra-band relaxation. Photon-density-dependent study shows that the broadened biexciton linewidth strongly depends on the MEG-induced extra-exciton generation. Long after the intra-band relaxation, the biexciton broadening is small and the single-exciton state filling is dominant.
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Affiliation(s)
- Younghwan Choi
- School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea
| | - Sangwan Sim
- School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea
| | - Seong Chu Lim
- IBS Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Daejon 305-701, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon, 440-746, Republic of Korea
| | - Young Hee Lee
- IBS Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Daejon 305-701, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon, 440-746, Republic of Korea
| | - Hyunyong Choi
- School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea
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19
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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
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20
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Aerts M, Spoor FCM, Grozema FC, Houtepen AJ, Schins JM, Siebbeles LDA. Cooling and Auger recombination of charges in PbSe nanorods: crossover from cubic to bimolecular decay. NANO LETTERS 2013; 13:4380-4386. [PMID: 23968451 DOI: 10.1021/nl402223q] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The cooling and Auger recombination of electron-hole pairs in PbSe quantum dots (QDs) and a series of nanorods (NRs) with similar diameter and varying length was studied by ultrafast pump-probe laser spectroscopy. Hot exciton cooling rates are found to be independent of nanocrystal shape. The energy relaxation rate decreases during cooling of charges, due to reduction of the density of electronic states. Auger recombination occurs via cubic third-order kinetics of uncorrelated charges in the QDs and NRs with length up to 29 nm. On increasing the NR length to 52 nm, a crossover to bimolecular exciton decay is found. This suggests a spatial extent of the one-dimensional exciton of 30-50 nm, which is significantly smaller than the value of 92 nm for the three-dimensional exciton diameter in bulk PbSe. The Auger decay time increases with NR length, which is beneficial for applications in nanocrystal lasers as well as for generation of free charges in photovoltaics.
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Affiliation(s)
- Michiel Aerts
- Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology , Julianalaan 136, 2628 BL Delft, The Netherlands
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21
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Jaeger HM, Hyeon-Deuk K, Prezhdo OV. Exciton multiplication from first principles. Acc Chem Res 2013; 46:1280-9. [PMID: 23459543 DOI: 10.1021/ar3002365] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Third-generation photovolatics require demanding cost and power conversion efficiency standards, which may be achieved through efficient exciton multiplication. Therefore, generating more than one electron-hole pair from the absorption of a single photon has vast ramifications on solar power conversion technology. Unlike their bulk counterparts, irradiated semiconductor quantum dots exhibit efficient exciton multiplication, due to confinement-enhanced Coulomb interactions and slower nonradiative losses. The exact characterization of the complicated photoexcited processes within quantum-dot photovoltaics is a work in progress. In this Account, we focus on the photophysics of nanocrystals and investigate three constituent processes of exciton multiplication, including photoexcitation, phonon-induced dephasing, and impact ionization. We quantify the role of each process in exciton multiplication through ab initio computation and analysis of many-electron wave functions. The probability of observing a multiple exciton in a photoexcited state is proportional to the magnitude of electron correlation, where correlated electrons can be simultaneously promoted across the band gap. Energies of multiple excitons are determined directly from the excited state wave functions, defining the threshold for multiple exciton generation. This threshold is strongly perturbed in the presence of surface defects, dopants, and ionization. Within a few femtoseconds following photoexcitation, the quantum state loses coherence through interactions with the vibrating atomic lattice. The phase relationship between single excitons and multiple excitons dissipates first, followed by multiple exciton fission. Single excitons are coupled to multiple excitons through Coulomb and electron-phonon interactions, and as a consequence, single excitons convert to multiple excitons and vice versa. Here, exciton multiplication depends on the initial energy and coupling magnitude and competes with electron-phonon energy relaxation. Multiple excitons are generated through impact ionization within picoseconds. The basis of exciton multiplication in quantum dots is the collective result of photoexcitation, dephasing, and nonadiabatic evolution. Each process is characterized by a distinct time-scale, and the overall multiple exciton generation dynamics is complete by about 10 ps. Without relying on semiempirical parameters, we computed quantum mechanical probabilities of multiple excitons for small model systems. Because exciton correlations and coherences are microscopic, quantum properties, results for small model systems can be extrapolated to larger, realistic quantum dots.
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Affiliation(s)
- Heather M. Jaeger
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Kim Hyeon-Deuk
- Department of Chemistry, Kyoto University, 606-8502, Kyoto, Japan
| | - Oleg V. Prezhdo
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
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22
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Zhu H, Yang Y, Lian T. Multiexciton annihilation and dissociation in quantum confined semiconductor nanocrystals. Acc Chem Res 2013; 46:1270-9. [PMID: 23148478 DOI: 10.1021/ar300202d] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Recent reports of multiexciton generation (MEG), a process by which one absorbed photon generates multiple excitons, in lead chalcogenide nanocrystals (NCs) have intensified research interest in using this phenomenon to improve the efficiency of solar energy conversion. Practical implementation of MEG processes in solar cells and solar-to-fuel conversion devices requires the development of materials with higher MEG efficiencies and lower excitation thresholds than are currently available, as well as schemes for efficient multiexciton extraction before the ultrafast exciton-exciton annihilation occurs. This Account focuses on the extraction of multiexcitons by interfacial electron transfer in model NC-molecular acceptor complexes. We provide an overview of multiexciton annihilation and multiexciton dissociation (MED) processes in NC-acceptor complexes of (i) CdSe quantum dots (QDs), (ii) CdSe/CdS quasi-type II core/shell QDs, (iii) CdSe quantum confined nanorods (QRs), and (iv) PbS QDs. We show that ultrafast electron transfer to adsorbed molecular acceptors can efficiently dissociate multiexcitons generated by absorption of multiple photons in (i), (ii), and (iii). Compared to core-only CdSe QDs, the electron hole distributions in CdSe/CdS quasi-type II QDs and CdSe QRs significantly improve their MED efficiencies by simultaneously retarding Auger recombination and facilitating interfacial electron transfer. Finally, in PbS-methylene blue (MB(+)) complexes, we show that the presence of electron acceptors does not affect the MEG efficiency and electron transfer to MB(+) efficiently dissociates the multiple excitons generated in PbS QDs. Our findings demonstrate that ultrafast interfacial charge transfer can be an efficient approach for extracting multiexcitons, and wavefunction engineering in quantum confined NCs can further improve MED efficiency.
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Affiliation(s)
- Haiming Zhu
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Ye Yang
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Tianquan Lian
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
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23
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Xiong W, Hickstein DD, Schnitzenbaumer KJ, Ellis JL, Palm BB, Keister KE, Ding C, Miaja-Avila L, Dukovic G, Jimenez JL, Murnane MM, Kapteyn HC. Photoelectron spectroscopy of CdSe nanocrystals in the gas phase: a direct measure of the evanescent electron wave function of quantum dots. NANO LETTERS 2013; 13:2924-2930. [PMID: 23688290 DOI: 10.1021/nl401309z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We present the first photoelectron spectroscopy measurements of quantum dots (semiconductor nanocrystals) in the gas phase. By coupling a nanoparticle aerosol source to a femtosecond velocity map imaging photoelectron spectrometer, we apply robust gas-phase photoelectron spectroscopy techniques to colloidal quantum dots, which typically must be studied in a liquid solvent or while bound to a surface. Working with a flowing aerosol of quantum dots offers the additional advantages of providing fresh nanoparticles for each laser shot and removing perturbations from bonding with a surface or interactions with the solvent. In this work, we perform a two-photon photoionization experiment to show that the photoelectron yield per exciton depends on the physical size of the quantum dot, increasing for smaller dots. Next, using effective mass modeling we show that the extent to which the electron wave function of the exciton extends from the quantum dot, the so-called "evanescent electron wavefunction", increases as the size of the quantum dot decreases. We show that the photoelectron yield is dominated by the evanescent electron density due to quantum confinement effects, the difference in the density of states inside and outside of the quantum dots, and the angle-dependent transmission probability of electrons through the surface of the quantum dot. Therefore, the photoelectron yield directly reflects the fraction of evanescent electron wave function that extends outside of the quantum dot. This work shows that gas-phase photoelectron spectroscopy is a robust and general probe of the electronic structure of quantum dots, enabling the first direct measurements of the evanescent exciton wave function.
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Affiliation(s)
- Wei Xiong
- Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado 80309, USA.
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24
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Ten Cate S, Liu Y, Suchand Sandeep CS, Kinge S, Houtepen AJ, Savenije TJ, Schins JM, Law M, Siebbeles LDA. Activating Carrier Multiplication in PbSe Quantum Dot Solids by Infilling with Atomic Layer Deposition. J Phys Chem Lett 2013; 4:1766-1770. [PMID: 26283107 DOI: 10.1021/jz4007492] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Carrier multiplication-the generation of multiple electron-hole pairs by a single photon-is currently of great interest for the development of highly efficient photovoltaics. We study the effects of infilling PbSe quantum-dot solids with metal oxides by atomic layer deposition on carrier multiplication. Using time-resolved microwave conductivity measurements, we find, for the first time, that carrier multiplication occurs in 1,2-ethanedithiol-linked PbSe quantum-dot solids infilled with Al2O3 or Al2O3/ZnO, while it is negligible or absent in noninfilled films. The carrier-multiplication efficiency of the infilled quantum-dot solids is close to that of solution-dispersed PbSe quantum dots, and not significantly limited by Auger recombination.
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Affiliation(s)
- Sybren Ten Cate
- †Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Yao Liu
- ‡Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States
| | - C S Suchand Sandeep
- †Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
| | | | - Arjan J Houtepen
- †Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Tom J Savenije
- †Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Juleon M Schins
- †Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Matt Law
- ‡Department of Chemistry, University of California, Irvine, Irvine, California 92697, United States
| | - Laurens D A Siebbeles
- †Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands
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25
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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.
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Affiliation(s)
- Kaifeng Wu
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA
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26
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Sippel P, Albrecht W, Mitoraj D, Eichberger R, Hannappel T, Vanmaekelbergh D. Two-photon photoemission study of competing Auger and surface-mediated relaxation of hot electrons in CdSe quantum dot solids. NANO LETTERS 2013; 13:1655-1661. [PMID: 23506122 DOI: 10.1021/nl400113t] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Solids composed of colloidal quantum dots hold promise for third generation highly efficient thin-film photovoltaic cells. The presence of well-separated conduction electron states opens the possibility for an energy-selective collection of hot and equilibrated carriers, pushing the efficiency above the one-band gap limit. However, in order to reach this goal the decay of hot carriers within a band must be better understood and prevented, eventually. Here, we present a two-photon photoemission study of the 1Pe→1Se intraband relaxation dynamics in a CdSe quantum dot solid that mimics the active layer in a photovoltaic cell. We observe fast hot electron relaxation from the 1Pe to the 1Se state on a femtosecond-scale by Auger-type energy donation to the hole. However, if the oleic acid capping is exchanged for hexanedithiol capping, fast deep hole trapping competes efficiently with this relaxation pathway, blocking the Auger-type electron-hole energy exchange. A slower decay becomes then visible; we provide evidence that this is a multistep process involving the surface.
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Affiliation(s)
- Philipp Sippel
- Helmholtz-Zentrum Berlin für Materialien und Energie, E-IF: Solar Fuels, Berlin, Germany
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27
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Abstract
The recent surge in the utilization of semiconductor nanostructures for solar energy conversion has led to the development of high-efficiency solar cells. Some of these recent advances are in the areas of synthesis of new semiconductor materials and the ability to tune the electronic properties through size, shape, and composition and to assemble quantum dots as hybrid assemblies. In addition, processes such as hot electron injection, multiple exciton generation (MEG), plasmonic effects, and energy-transfer-coupled electron transfer are gaining momentum to overcome the efficiency limitations of energy capture and conversion. The recent advances as well as future prospects of quantum dot solar cells discussed in this perspective provide the basis for consideration as "The Next Big Thing" in photovoltaics.
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Affiliation(s)
- Prashant V Kamat
- Radiation Laboratory and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
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28
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Padilha LA, Stewart JT, Sandberg RL, Bae WK, Koh WK, Pietryga JM, Klimov VI. Aspect ratio dependence of auger recombination and carrier multiplication in PbSe nanorods. NANO LETTERS 2013; 13:1092-9. [PMID: 23360573 DOI: 10.1021/nl304426y] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Nanomaterials with efficient carrier multiplication (CM), that is, generation of multiple electron-hole pairs by single photons, have been the object of intense scientific interest as potential enablers of high efficiency generation-III photovoltaics. In this work, we explore nanocrystal shape control as a means for enhancing CM. Specifically, we investigate the influence of aspect ratio (ρ) of PbSe nanorods (NRs) on both CM and the inverse of this process, Auger recombination. We observe that Auger lifetimes in NRs increase with increasing particle volume and for a fixed cross-sectional size follow a linear dependence on the NR length. For a given band gap energy, the CM efficiency in NRs shows a significant dependence on aspect ratio and exhibits a maximum at ρ ∼ 6-7 for which the multiexciton yields are a factor of ca. 2 higher than those in quantum dots with a similar bandgap energy. To rationalize our experimental observations, we analyze the influence of dimensionality on both CM and non-CM energy-loss mechanisms and offer possible explanations for the seemingly divergent effects the transition from zero- to one-dimensional confinement has on the closely related processes of Auger recombination and CM.
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Affiliation(s)
- Lazaro A Padilha
- Center for Advanced Solar Photophysics, Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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29
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Williams KJ, Nelson CA, Yan X, Li LS, Zhu X. Hot electron injection from graphene quantum dots to TiO₂. ACS NANO 2013; 7:1388-94. [PMID: 23347000 DOI: 10.1021/nn305080c] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The Shockley-Queisser limit is the maximum power conversion efficiency of a conventional solar cell based on a single semiconductor junction. One approach to exceed this limit is to harvest hot electrons/holes that have achieved quasi-equilibrium in the light absorbing material with electronic temperatures higher than the phonon temperature. We argue that graphene based materials are viable candidates for hot carrier chromophores. Here we probe hot electron injection and charge recombination dynamics for graphene quantum dots (QDs, each containing 48 fused benzene rings) anchored to the TiO₂(110) surface via carboxyl linkers. We find ultrafast electron injection from photoexcited graphene QDs to the TiO₂ conduction band with time constant τ(i) < 15 fs and charge recombination dynamics characterized by a fast channel (τ(r1) = 80-130 fs) and a slow one (τ(r2) = 0.5-2 ps). The fast decay channel is attributed to the prompt recombination of the bound electron-hole pair across the interface. The slow channel depends strongly on excitation photon energy or sample temperature and can be explained by a "boomerang" mechanism, in which hot electrons are injected into bulk TiO₂, cooled down due to electron-phonon scattering, drifted back to the interface under the transient electric field, and recombine with the hole on graphene QDs. We discuss feasibilities of implementing the hot carrier solar cell using graphene nanomaterials.
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Affiliation(s)
- Kenrick J Williams
- Department of Chemistry & Biochemistry, University of Texas, Austin, Texas 78712, USA
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30
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Sandberg RL, Padilha LA, Qazilbash MM, Bae WK, Schaller RD, Pietryga JM, Stevens MJ, Baek B, Nam SW, Klimov VI. Multiexciton dynamics in infrared-emitting colloidal nanostructures probed by a superconducting nanowire single-photon detector. ACS NANO 2012; 6:9532-9540. [PMID: 23020520 DOI: 10.1021/nn3043226] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Carrier multiplication (CM) is the process in which absorption of a single photon produces multiple electron-hole pairs. Here, we evaluate the effect of particle shape on CM efficiency by conducting a comparative study of spherical nanocrystal quantum dots (NQDs) and elongated nanorods (NRs) of PbSe using a time-resolved technique that is based on photon counting in the infrared using a superconducting nanowire single-photon photodetector (SNSPD). Due to its high sensitivity and low noise levels, this technique allows for accurate determination of CM yields, even with the small excitation intensities required for quantitative measurements, and the fairly low emission quantum yields of elongated NR samples. Our measurements indicate an up to ∼60% increase in multiexciton yields in NRs versus NQDs, which is attributed primarily to a decrease in the electron-hole pair creation energy. These findings suggest that shape control is a promising approach for enhancing the CM process. Further, our work demonstrates the effectiveness of the SNSPD technique for the rapid screening of CM performance in infrared nanomaterials.
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Affiliation(s)
- Richard L Sandberg
- Center for Advanced Solar Photophysics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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