1
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Zhang H, Debroye E, Vina-Bausa B, Valli D, Fu S, Zheng W, Di Virgilio L, Gao L, Frost JM, Walsh A, Hofkens J, Wang HI, Bonn M. Stable Mott Polaron State Limits the Charge Density in Lead Halide Perovskites. ACS ENERGY LETTERS 2023; 8:420-428. [PMID: 36660369 PMCID: PMC9841606 DOI: 10.1021/acsenergylett.2c01949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 12/05/2022] [Indexed: 06/17/2023]
Abstract
Large polarons are known to form in lead halide perovskites (LHPs). Photoinduced isolated polarons at low densities have been well-researched, but many-body interactions at elevated polaron densities, exceeding the Mott criterion (i.e., Mott polaron density), have remained elusive. Here, employing ultrafast terahertz spectroscopy, we identify a stable Mott polaron state in LHPs at which the polaron wavefunctions start to overlap. The Mott polaron density is determined to be ∼1018 cm-3, in good agreement with theoretical calculations based on the Feynman polaron model. The electronic phase transition across the Mott density is found to be universal in LHPs and independent of the constituent ions. Exceeding the Mott polaron density, excess photoinjected charge carriers annihilate quickly within tens to hundreds of picoseconds, before reaching the stable and long-lived Mott state. These results have considerable implications for LHP-based devices and for understanding exotic phenomena reported in LHPs.
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Affiliation(s)
- Heng Zhang
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128Mainz, Germany
| | - Elke Debroye
- Department
of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001Leuven, Belgium
| | - Beatriz Vina-Bausa
- Department
of Physics, Imperial College London, Exhibition Road, LondonSW7 2AZ, United Kingdom
| | - Donato Valli
- Department
of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001Leuven, Belgium
| | - Shuai Fu
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128Mainz, Germany
| | - Wenhao Zheng
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128Mainz, Germany
| | - Lucia Di Virgilio
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128Mainz, Germany
| | - Lei Gao
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128Mainz, Germany
- School
of Physics and Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing211189, China
| | - Jarvist M. Frost
- Department
of Physics, Imperial College London, Exhibition Road, LondonSW7 2AZ, United Kingdom
| | - Aron Walsh
- Department
of Materials, Imperial College London, Exhibition Road, LondonSW7 2AZ, United Kingdom
| | - Johan Hofkens
- Department
of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001Leuven, Belgium
| | - Hai I. Wang
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128Mainz, Germany
| | - Mischa Bonn
- Max
Planck Institute for Polymer Research, Ackermannweg 10, 55128Mainz, Germany
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2
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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
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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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3
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Liu H, Luo G, Cheng H, Yang Z, Xie Z, Zhang KHL, Yang Y. Ultrafast Anisotropic Evolution of Photoconductivity in Sb 2Se 3 Single Crystals. J Phys Chem Lett 2022; 13:4988-4994. [PMID: 35648596 DOI: 10.1021/acs.jpclett.2c01346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The antimony chalcogenide crystals are composed of quasi-one-dimensional [Sb4X6]n ribbons, which lead to strong anisotropic optical and electronic properties. An attempt to exploit photoconductivity anisotropy in the device fabrication may introduce a rewarding strategy to propel the development of the antimony chalcogenide solar cells. To achieve this, understanding of the dynamic evolution of the photoconductivity anisotropy is required. Here, the photoconductivities along different lattice directions in an antimony selenide single crystal are investigated by time-resolved terahertz spectroscopy. We find that electron trapping results in a variation of the photoconductivity anisotropy accompanied by a decrease in the photoconductivity magnitude, while electron-hole recombination only reduces the magnitude but does not affect the anisotropy. Therefore, measuring the temporal evolution of photoconductivity anisotropy can provide a wealth of information regarding the nature of the photocarrier and also render a probe to selectively evaluate the photoconductivity decay mechanisms.
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Affiliation(s)
- Huijie Liu
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
| | - Geying Luo
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
| | - Haoran Cheng
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
| | - Zhangqiang Yang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
| | - Zhaoxiong Xie
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
| | - Kelvin H L Zhang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
| | - Ye Yang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, People's Republic of China
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4
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Ballabio M, Fuertes Marrón D, Barreau N, Bonn M, Cánovas E. Composition-Dependent Passivation Efficiency at the CdS/CuIn 1- x Ga x Se 2 Interface. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1907763. [PMID: 31984586 DOI: 10.1002/adma.201907763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 12/24/2019] [Indexed: 06/10/2023]
Abstract
The bandgap of CuIn1- x Gax Se2 (CIGS) chalcopyrite semiconductors can be tuned between ≈1.0 and ≈1.7 eV for Ga contents ranging between x = 0 and x = 1. While an optimum bandgap of 1.34 eV is desirable for achieving maximum solar energy conversion in solar cells, state-of-the-art CIGS-based devices experience a drop in efficiency for Ga contents x > 0.3 (i.e., for bandgaps >1.2 eV), an aspect that is limiting the full potential of these devices. The mechanism underlying the limited performance as a function of CIGS composition has remained elusive: both surface and bulk recombination effects are proposed. Here, the disentanglement between surface and bulk effects in CIGS absorbers as a function of Ga content is achieved by comparing photogenerated charge carrier dynamics in air/CIGS and surface-passivated ZnO/CdS/CIGS samples. While surface passivation prevents surface recombination of charge carriers for low Ga content (x < 0.3; up to 1.2 eV bandgap), surface recombination dominates for higher-bandgap materials. The results thus demonstrate that surface, rather than bulk effects, is responsible for the drop in efficiency for Ga contents larger than x ≈ 0.3.
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Affiliation(s)
- Marco Ballabio
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
| | - David Fuertes Marrón
- Instituto de Energía Solar, Universidad Politécnica de Madrid, ETSI Telecomunicación, Avda. Complutense 30, 28040, Madrid, Spain
| | - Nicolas Barreau
- Institut des Matériaux Jean Rouxel (IMN) - UMR6502, Université de Nantes, CNRS, 2 rue de la Houssinière, BP 32229, 44322, Nantes Cedex 3, France
| | - Mischa Bonn
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
| | - Enrique Cánovas
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia), Faraday 9, 28049, Madrid, Spain
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5
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Zhang Y, Wu G, Liu F, Ding C, Zou Z, Shen Q. Photoexcited carrier dynamics in colloidal quantum dot solar cells: insights into individual quantum dots, quantum dot solid films and devices. Chem Soc Rev 2020; 49:49-84. [PMID: 31825404 DOI: 10.1039/c9cs00560a] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The certified power conversion efficiency (PCE) record of colloidal quantum dot solar cells (QDSCs) has considerably improved from below 4% to 16.6% in the last few years. However, the record PCE value of QDSCs is still substantially lower than the theoretical efficiency. So far, there have been several reviews on recent and significant achievements in QDSCs, but reviews on photoexcited carrier dynamics in QDSCs are scarce. The photovoltaic performances of QDSCs are still limited by the photovoltage, photocurrent and fill factor that are mainly determined by the photoexcited carrier dynamics, including carrier (or exciton) generation, carrier extraction or transfer, and the carrier recombination process, in the devices. In this review, the photoexcited carrier dynamics in the whole QDSCs, originating from individual quantum dots (QDs) to the entire device as well as the characterization methods used for analyzing the photoexcited carrier dynamics are summarized and discussed. The recent research including photoexcited multiple exciton generation (MEG), hot electron extraction, and carrier transfer between adjacent QDs, as well as carrier injection and recombination at each interface of QDSCs are discussed in detail herein. The influence of photoexcited carrier dynamics on the physiochemical properties of QDs and photovoltaic performances of QDSC devices is also discussed.
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Affiliation(s)
- Yaohong Zhang
- Faculty of Informatics and Engineering, The University of Electro-Communications, Tokyo 182-8585, Japan.
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6
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Wang K, Chen C, Liao H, Wang S, Tang J, Beard MC, Yang Y. Both Free and Trapped Carriers Contribute to Photocurrent of Sb 2Se 3 Solar Cells. J Phys Chem Lett 2019; 10:4881-4887. [PMID: 31401837 DOI: 10.1021/acs.jpclett.9b01817] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Polycrystalline semiconductor films, such as methylammonium lead iodide, cadmium telluride, copper-indium-gallium selenide, etc., are being intensively studied because of their great potential for highly efficient and cost-effective solar cells. Among them, polycrystalline antimony chalcogenide films are also promising for photovoltaic applications because they are nontoxic, stable, and flexible and have a suitable band gap. Considerable effort has already been devoted to improving the power conversion efficiency of antimony chalcogenide solar cells, but their efficiency still lingers below 10% due in part to scarce fundamental optoelectronic studies that help guide their development. Here, we use a combination of time-resolved terahertz and transient absorption spectroscopies to interrogate the optoelectronic behavior of antimony selenide thin films. By combining these two techniques we are able to monitor both free and trapped carrier dynamics and then evaluate their respective diffusion lengths. Our results indicate that trapped carriers remain mobile and can reach charge-collecting interfaces prior to recombination, and therefore, both free and trapped carriers can contribute to the photocurrent of antimony selenide solar cells.
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Affiliation(s)
- Kang Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Chao Chen
- Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, China
| | - Hongyan Liao
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Siyu Wang
- Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, China
| | - Jiang Tang
- Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, China
| | - Matthew C Beard
- Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Ye Yang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
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7
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Minority and Majority Charge Carrier Mobility in Cu 2ZnSnSe 4 revealed by Terahertz Spectroscopy. Sci Rep 2018; 8:14476. [PMID: 30262870 PMCID: PMC6160416 DOI: 10.1038/s41598-018-32695-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 09/12/2018] [Indexed: 11/18/2022] Open
Abstract
The mobilities of electrons and holes determine the applicability of any semiconductor, but their individual measurement remains a major challenge. Here, we show that time-resolved terahertz spectroscopy (TRTS) can distinguish the mobilities of minority and majority charge carriers independently of the doping-type and without electrical contacts. To this end, we combine the well-established determination of the sum of electron and hole mobilities from photo-induced THz absorption spectra with mobility-dependent ambipolar modeling of TRTS transients. The method is demonstrated on a polycrystalline Cu2ZnSnSe4 thin film and reveals a minority (electron) mobility of 128 cm2/V-s and a majority (hole) carrier mobility of 7 cm2/V-s in the vertical transport direction relevant for light emitting, photovoltaic and solar water splitting devices. Additionally, the TRTS analysis yields an effective bulk carrier lifetime of 4.4 ns, a surface recombination velocity of 6 * 104 cm/s and a doping concentration of ca. 1016 cm−3, thus offering the potential for contactless screen novel optoelectronic materials.
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8
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Hempel H, Unold T, Eichberger R. Measurement of charge carrier mobilities in thin films on metal substrates by reflection time resolved terahertz spectroscopy. OPTICS EXPRESS 2017; 25:17227-17236. [PMID: 28789216 DOI: 10.1364/oe.25.017227] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Accepted: 04/11/2017] [Indexed: 06/07/2023]
Abstract
We show that charge carrier mobilities can be measured by reflection time resolved THz spectroscopy (R-TRTS) even for thin films on metal contacts, such as polycrystalline Cu2SnZnSe4 grown on molybdenum. In the measurement a reduced THz reflection upon photo-excitation is observed in contrast to increased THz reflection commonly observed on insulating substrates, and which excludes standard analytic R-TRTS analyses. Instead, a numerical transfer matrix method is used to model the THz reflection from which we derive carrier mobilities of 100 cm2/Vs consistent with literature. We show that R-TRTS on metal substrates is ~100x less sensitive compared to measurements on insulating substrates. These sensitivity of these R-TRTS measurements can be increased by using lower substrate refractive indices, lower substrate conductivities, thicker sample layers or higher THz probe frequencies.
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9
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Zhang W, Zeng X, Su X, Zou X, Mante PA, Borgström MT, Yartsev A. Carrier Recombination Processes in Gallium Indium Phosphide Nanowires. NANO LETTERS 2017; 17:4248-4254. [PMID: 28654299 DOI: 10.1021/acs.nanolett.7b01159] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Understanding of recombination and photoconductivity dynamics of photogenerated charge carriers in GaxIn1-xP NWs is essential for their optoelectronic applications. In this letter, we have studied a series of GaxIn1-xP NWs with varied Ga composition. Time-resolved photoinduced luminescence, femtosecond transient absorption, and time-resolved THz transmission measurements were performed to assess radiative and nonradiative recombination and photoconductivity dynamics of photogenerated charges in the NWs. We conclude that radiative recombination dynamics is limited by hole trapping, whereas electrons are highly mobile until they recombine nonradiatively. We also resolve gradual decrease of mobility of photogenerated electrons assigned to electron trapping and detrapping in a distribution of trap states. We identify that the nonradiative recombination of charges is much slower than the decay of the photoluminescence signal. Further, we conclude that trapping of both electrons and holes as well as nonradiative recombination become faster with increasing Ga composition in GaxIn1-xP NWs. We have estimated early time electron mobility in GaxIn1-xP NWs and found it to be strongly dependent on Ga composition due to the contribution of electrons in the X-valley.
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Affiliation(s)
- Wei Zhang
- NanoLund and Division of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden
| | - Xulu Zeng
- NanoLund and Division of Solid State Physics, Lund University , Box 118, 221 00 Lund, Sweden
| | - Xiaojun Su
- NanoLund and Division of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden
| | - Xianshao Zou
- NanoLund and Division of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden
| | - Pierre-Adrien Mante
- NanoLund and Division of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden
| | - Magnus T Borgström
- NanoLund and Division of Solid State Physics, Lund University , Box 118, 221 00 Lund, Sweden
| | - Arkady Yartsev
- NanoLund and Division of Chemical Physics, Lund University , Box 124, 221 00 Lund, Sweden
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10
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Bergren MR, Palomaki PKB, Neale NR, Furtak TE, Beard MC. Size-Dependent Exciton Formation Dynamics in Colloidal Silicon Quantum Dots. ACS NANO 2016; 10:2316-23. [PMID: 26811876 DOI: 10.1021/acsnano.5b07073] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We report size-dependent exciton formation dynamics within colloidal silicon quantum dots (Si QDs) using time-resolved terahertz (THz) spectroscopy measurements. THz photoconductivity measurements are used to distinguish the initially created hot carriers from excitons that form at later times. At early pump/probe delays, the exciton formation dynamics are revealed by the temporal evolution of the THz transmission. We find an increase in the exciton formation time, from ∼500 to ∼900 fs, as the Si QD diameter is reduced from 7.3 to 3.4 nm and all sizes exhibit slower hot-carrier relaxation times compared to bulk Si. In addition, we determine the THz absorption cross section at early delay times is proportional to the carrier mobility while at later delays is proportional to the exciton polarizability, αX. We extract a size-dependent αX and find an ∼r(4) dependence, consistent with previous reports for quantum-confined excitons in CdSe, InAs, and PbSe QDs. The observed slowing in exciton formation time for smaller Si QDs is attributed to decreased electron-phonon coupling due to increased quantum confinement. These results experimentally verify the modification of hot-carrier relaxation rates by quantum confinement in Si QDs, which likely plays a significant role in the high carrier multiplication efficiency observed in these nanomaterials.
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Affiliation(s)
- Matthew R Bergren
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
- Physics Department, Colorado School of Mines , Golden, Colorado 80401, United States
| | - Peter K B Palomaki
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
| | - Nathan R Neale
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
| | - Thomas E Furtak
- Physics Department, Colorado School of Mines , Golden, Colorado 80401, United States
| | - Matthew C Beard
- National Renewable Energy Laboratory , Golden, Colorado 80401, United States
- Physics Department, Colorado School of Mines , Golden, Colorado 80401, United States
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11
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Guo X, Chen H, Wen X, Zheng J. Electron-phonon interactions in MoS2 probed with ultrafast two-dimensional visible/far-infrared spectroscopy. J Chem Phys 2015; 142:212447. [DOI: 10.1063/1.4921573] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Xunmin Guo
- Department of Chemistry, Rice University, 6100 Main Street, Houston, Texas 77005-1892, USA
| | - Hailong Chen
- Department of Chemistry, Rice University, 6100 Main Street, Houston, Texas 77005-1892, USA
| | - Xiewen Wen
- Department of Chemistry, Rice University, 6100 Main Street, Houston, Texas 77005-1892, USA
| | - Junrong Zheng
- Department of Chemistry, Rice University, 6100 Main Street, Houston, Texas 77005-1892, USA
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12
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Hamm P. 2D-Raman-THz spectroscopy: a sensitive test of polarizable water models. J Chem Phys 2015; 141:184201. [PMID: 25399140 DOI: 10.1063/1.4901216] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
In a recent paper, the experimental 2D-Raman-THz response of liquid water at ambient conditions has been presented [J. Savolainen, S. Ahmed, and P. Hamm, Proc. Natl. Acad. Sci. U. S. A. 110, 20402 (2013)]. Here, all-atom molecular dynamics simulations are performed with the goal to reproduce the experimental results. To that end, the molecular response functions are calculated in a first step, and are then convoluted with the laser pulses in order to enable a direct comparison with the experimental results. The molecular dynamics simulation are performed with several different water models: TIP4P/2005, SWM4-NDP, and TL4P. As polarizability is essential to describe the 2D-Raman-THz response, the TIP4P/2005 water molecules are amended with either an isotropic or a anisotropic polarizability a posteriori after the molecular dynamics simulation. In contrast, SWM4-NDP and TL4P are intrinsically polarizable, and hence the 2D-Raman-THz response can be calculated in a self-consistent way, using the same force field as during the molecular dynamics simulation. It is found that the 2D-Raman-THz response depends extremely sensitively on details of the water model, and in particular on details of the description of polarizability. Despite the limited time resolution of the experiment, it could easily distinguish between various water models. Albeit not perfect, the overall best agreement with the experimental data is obtained for the TL4P water model.
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Affiliation(s)
- Peter Hamm
- Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
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13
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Direct observation of the collapse of the delocalized excess electron in water. Nat Chem 2014; 6:697-701. [PMID: 25054939 DOI: 10.1038/nchem.1995] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 06/04/2013] [Indexed: 12/26/2022]
Abstract
It is generally assumed that the hydrated electron occupies a quasi-spherical cavity surrounded by only a few water molecules in its equilibrated state. However, in the very moment of its generation, before water has had time to respond to the extra charge, it is expected to be significantly larger in size. According to a particle-in-a-box picture, the frequency of its absorption spectrum is a sensitive measure of the initial size of the electronic wavefunction. Here, using transient terahertz spectroscopy, we show that the excess electron initially absorbs in the far-infrared at a frequency for which accompanying ab initio molecular dynamics simulations estimate an initial delocalization length of ≈ 40 Å. The electron subsequently shrinks due to solvation and thereby leaves the terahertz observation window very quickly, within ≈ 200 fs.
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14
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Bergren MR, Kendrick CE, Neale NR, Redwing JM, Collins RT, Furtak TE, Beard MC. Ultrafast Electrical Measurements of Isolated Silicon Nanowires and Nanocrystals. J Phys Chem Lett 2014; 5:2050-2057. [PMID: 26270492 DOI: 10.1021/jz500863a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We simultaneously determined the charge carrier mobility and picosecond to nanosecond carrier dynamics of isolated silicon nanowires (Si NWs) and nanocrystals (Si NCs) using time-resolved terahertz spectroscopy. We then compared these results to data measured on bulk c-Si as a function of excitation fluence. We find >1 ns carrier lifetimes in Si NWs that are dominated by surface recombination with surface recombination velocities (SRV) between ∼1100-1700 cm s(-1) depending on process conditions. The Si NCs have markedly different decay dynamics. Initially, free-carriers are produced, but relax within ∼1.5 ps to form bound excitons. Subsequently, the excitons decay with lifetimes >7 ns, similar to free carriers produced in bulk Si. The isolated Si NWs exhibit bulk-like mobilities that decrease with increasing excitation density, while the hot-carrier mobilities in the Si NCs are lower than bulk mobilities and could only be measured within the initial 1.5 ps decay. We discuss the implications of our measurements on the utilization of Si NWs and NCs in macroscopic optoelectronic applications.
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Affiliation(s)
- Matthew R Bergren
- †Physics Department, Colorado School of Mines, Golden, Colorado 80401, United States
- ‡Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Chito E Kendrick
- †Physics Department, Colorado School of Mines, Golden, Colorado 80401, United States
- §Materials Science and Engineering Department, Penn State University, State College, Pennsylvania 16801, United States
| | - Nathan R Neale
- ‡Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Joan M Redwing
- §Materials Science and Engineering Department, Penn State University, State College, Pennsylvania 16801, United States
| | - Reuben T Collins
- †Physics Department, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Thomas E Furtak
- †Physics Department, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Matthew C Beard
- †Physics Department, Colorado School of Mines, Golden, Colorado 80401, United States
- ‡Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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15
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Ahmed S, Savolainen J, Hamm P. The effect of the Gouy phase in optical-pump-THz-probe spectroscopy. OPTICS EXPRESS 2014; 22:4256-4266. [PMID: 24663749 DOI: 10.1364/oe.22.004256] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We show theoretically as well as experimentally that the Gouy-phase shift, which depends on the exact positioning of a sample in relation to the focus of a probe beam in a pump-probe experiment, may have a pronounced effect on the shape of the pump-probe signal. The effect occurs only when single-cycle probe pulses are used, i.e. when the slowly varying envelope approximation breaks down, while it disappears for multi-cycle pulses. The effect is thus most relevant in THz time-resolved spectroscopy, where such single cycle pulses are most commonly used, but it should not be overlooked also in other spectral regimes when correspondingly short pulses are involved.
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Abstract
Two-dimensional Raman-terahertz (THz) spectroscopy is presented as a multidimensional spectroscopy directly in the far-IR regime. The method is used to explore the dynamics of the collective intermolecular modes of liquid water at ambient temperatures that emerge from the hydrogen-bond networks water forming. Two-dimensional Raman-THz spectroscopy interrogates these modes twice and as such can elucidate couplings and inhomogeneities of the various degrees of freedoms. An echo in the 2D Raman-THz response is indeed identified, indicating that a heterogeneous distribution of hydrogen-bond networks exists, albeit only on a very short 100-fs timescale. This timescale appears to be too short to be compatible with more extended, persistent structures assumed within a two-state model of water.
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Liu HW, Wong LM, Wang SJ, Tang SH, Zhang XH. Ultrafast insulator–metal phase transition in vanadium dioxide studied using optical pump–terahertz probe spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:415604. [PMID: 23014464 DOI: 10.1088/0953-8984/24/41/415604] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We studied the ultrafast dynamic behavior of the photoinduced insulator–metal phase transition in VO2 thin film using optical pump–terahertz probe spectroscopy with different excitation fluences and at different temperatures. We observed two processes in the insulator–metal phase transition in VO2: a fast process and a slow process. The fast process is a nonthermal process, which is ascribed to the nucleation of the metal phase, while the slow process is strongly affected by temperature and is ascribed to the thermally driven growth and coalescence of metal domains in VO2. The transient complex conductivity spectra at different delay times are also investigated.
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Affiliation(s)
- H W Liu
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore
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Tang H, Zhu LG, Zhao L, Zhang X, Shan J, Lee ST. Carrier dynamics in Si nanowires fabricated by metal-assisted chemical etching. ACS NANO 2012; 6:7814-7819. [PMID: 22891641 DOI: 10.1021/nn301891s] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Silicon nanowire arrays fabricated by metal-assisted wet chemical etching have emerged as a promising architecture for solar energy harvesting applications. Here we investigate the dynamics and transport properties of photoexcited carriers in nanowires derived from an intrinsic silicon wafer using the terahertz (THz) time-domain spectroscopy. Both the dynamics and the pump fluence dependence of the photoinduced complex conductivity spectra up to several THz were measured. The photoinduced conductivity spectra follow a Lorentz dependence, arising from surface plasmon resonances in nanowires. The carrier lifetime was observed to approach 0.7 ns, which is limited primarily by surface trapping. The intrinsic carrier mobility was found to be ~1000 cm(2)/(V · s). Compared to other silicon nanostructures, these relative high values observed for both the carrier lifetime and mobility are the consequences of high crystallinity and surface quality of the nanowires fabricated by the metal-assisted wet chemical etching method.
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Affiliation(s)
- Hao Tang
- Center of Super-Diamond and Advanced Films and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China
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Parkinson P, Dodson C, Joyce HJ, Bertness KA, Sanford NA, Herz LM, Johnston MB. Noncontact measurement of charge carrier lifetime and mobility in GaN nanowires. NANO LETTERS 2012; 12:4600-4604. [PMID: 22924866 DOI: 10.1021/nl301898m] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The first noncontact photoconductivity measurements of gallium nitride nanowires (NWs) are presented, revealing a high crystallographic and optoelectronic quality achieved by use of catalyst-free molecular beam epitaxy. In comparison with bulk material, the NWs exhibit a long conductivity lifetime (>2 ns) and a high mobility (820 ± 120 cm(2)/(V s)). This is due to the weak influence of surface traps with respect to other III-V semiconducting NWs and to the favorable crystalline structure of the NWs achieved via strain-relieved growth.
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Affiliation(s)
- Patrick Parkinson
- Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia.
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Němec H, Kratochvílová I, Kužel P, Šebera J, Kochalska A, Nožár J, Nešpůrek S. Charge carrier mobility in poly[methyl(phenyl)silylene] studied by time-resolved terahertz spectroscopy and molecular modelling. Phys Chem Chem Phys 2010; 13:2850-6. [PMID: 21305068 DOI: 10.1039/c0cp00774a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Time-resolved terahertz spectroscopy and combination of quantum chemistry modeling and molecular dynamics simulations were used for the determination of charge carrier mobility in poly[methyl(phenyl)silylene]. Using time-resolved THz spectroscopy we established the on-chain charge carrier drift mobility in PMPSi as 0.02 cm(2) V(-1) s(-1). This value is low due to the formation of polarons: the hole is self-trapped in a potential formed by local chain distortion and the transient THz conductivity spectra show signatures of its oscillations within this potential well. This view is supported by the agreement between experimental and calculated values of the on-chain charge carrier mobility.
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Affiliation(s)
- Hynek Němec
- Institute of Physics AS CR, Na Slovance 2, 182 21 Prague 8, Czech Republic.
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Charge transport in nanostructured materials for solar energy conversion studied by time-resolved terahertz spectroscopy. J Photochem Photobiol A Chem 2010. [DOI: 10.1016/j.jphotochem.2010.08.006] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Parkinson P, Joyce HJ, Gao Q, Tan HH, Zhang X, Zou J, Jagadish C, Herz LM, Johnston MB. Carrier lifetime and mobility enhancement in nearly defect-free core-shell nanowires measured using time-resolved terahertz spectroscopy. NANO LETTERS 2009; 9:3349-53. [PMID: 19736975 DOI: 10.1021/nl9016336] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.
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Affiliation(s)
- Patrick Parkinson
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
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