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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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Alamoudi M, Katsiev K, Idriss H. Monitoring the Lifetime of Photoexcited Electrons in a Fresh and Bulk Reduced Rutile TiO 2 Single Crystal. Possible Anisotropic Propagation. J Phys Chem Lett 2023; 14:9238-9244. [PMID: 37811922 DOI: 10.1021/acs.jpclett.3c02301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
Defects (oxygen vacancies and interstitial cations) in oxide semiconductors have recently been invoked as a key property behind increased photocatalytic reaction rates. In this work, we have monitored by transient absorption spectroscopy (TAS) excited electrons in the conduction band decaying into the invoked traps to extract their lifetime using a rutile single crystal instead of the more conveniently used powder homologue. This is preferred in order to rule out grain boundary, degree of crystallinity, and size effects among other parameters that would obscure the results. It was found, in the energy region investigated (1.3-1.8 eV), that the lifetime of excited electrons is about four times shorter for the bulk defect crystal when compared to the fresh one. This indicates that the created defects (mostly oxygen defects and interstitial Ti cations) are unlikely to contribute to reaction rate enhancement.
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Affiliation(s)
- M Alamoudi
- Surface Science and Advanced Characterization, SABIC-CRD at KAUST, Thuwal 23955, Saudi Arabia
| | - K Katsiev
- Surface Science and Advanced Characterization, SABIC-CRD at KAUST, Thuwal 23955, Saudi Arabia
| | - H Idriss
- Institute of Functional Interfaces, Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
- Department of Chemistry, University College London, WC1H 0AH London, U.K
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3
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Wagstaffe M, Dominguez-Castro A, Wenthaus L, Palutke S, Kutnyakhov D, Heber M, Pressacco F, Dziarzhytski S, Gleißner H, Gupta VK, Redlin H, Dominguez A, Frauenheim T, Rubio A, Stierle A, Noei H. Photoinduced Dynamics at the Water/TiO_{2}(101) Interface. PHYSICAL REVIEW LETTERS 2023; 130:108001. [PMID: 36962043 DOI: 10.1103/physrevlett.130.108001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Accepted: 01/17/2023] [Indexed: 06/18/2023]
Abstract
We present a femtosecond time-resolved optical pump-soft x-ray probe photoemission study in which we follow the dynamics of charge transfer at the interface of water and anatase TiO_{2}(101). By combining our observation of transient oxygen O 1s core level peak shifts at submonolayer water coverages with Ehrenfest molecular dynamics simulations we find that ultrafast interfacial hole transfer from TiO_{2} to molecularly adsorbed water is completed within the 285 fs time resolution of the experiment. This is facilitated by the formation of a new hydrogen bond between an O_{2c} site at the surface and a physisorbed water molecule. The calculations fully corroborate our experimental observations and further suggest that this process is preceded by the efficient trapping of the hole at the surface of TiO_{2} by hydroxyl species (-OH), that form following the dissociative adsorption of water. At a water coverage exceeding a monolayer, interfacial charge transfer is suppressed. Our findings are directly applicable to a wide range of photocatalytic systems in which water plays a critical role.
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Affiliation(s)
- Michael Wagstaffe
- Centre for X-ray and Nanoscience (CXNS), Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany
| | - Adrian Dominguez-Castro
- Bremen Center for Computational Material Science (BCCMS), University of Bremen, Am Fallturm 1, 28359 Bremen, Germany
| | - Lukas Wenthaus
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85 D-22607, Hamburg, Germany
| | - Steffen Palutke
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85 D-22607, Hamburg, Germany
| | - Dmytro Kutnyakhov
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85 D-22607, Hamburg, Germany
| | - Michael Heber
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85 D-22607, Hamburg, Germany
| | - Federico Pressacco
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85 D-22607, Hamburg, Germany
| | | | - Helena Gleißner
- Centre for X-ray and Nanoscience (CXNS), Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany
- Fachbereich Physik Universität Hamburg, Jungiusstr. 9-11, D-20355, Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Verena Kristin Gupta
- Bremen Center for Computational Material Science (BCCMS), University of Bremen, Am Fallturm 1, 28359 Bremen, Germany
| | - Harald Redlin
- Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85 D-22607, Hamburg, Germany
| | - Adriel Dominguez
- Bremen Center for Computational Material Science (BCCMS), University of Bremen, Am Fallturm 1, 28359 Bremen, Germany
- Computational Science and Applied Research Institute (CSAR), 518110, Shenzhen, China
- Beijing Computational Science Research Center (CSRC), 100193, Beijing, China
- Nano-Bio Spectroscopy Group, Departamento de Fisica de Materiales, Universidad del País Vasco, UPV/EHU- 20018 San Sebastián, Spain
| | - Thomas Frauenheim
- Bremen Center for Computational Material Science (BCCMS), University of Bremen, Am Fallturm 1, 28359 Bremen, Germany
- Computational Science and Applied Research Institute (CSAR), 518110, Shenzhen, China
- Beijing Computational Science Research Center (CSRC), 100193, Beijing, China
| | - Angel Rubio
- Nano-Bio Spectroscopy Group, Departamento de Fisica de Materiales, Universidad del País Vasco, UPV/EHU- 20018 San Sebastián, Spain
- Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
- Center for Computational Quantum Physics, Flatiron Institute, New York 10010, New York, USA
| | - Andreas Stierle
- Centre for X-ray and Nanoscience (CXNS), Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany
- Fachbereich Physik Universität Hamburg, Jungiusstr. 9-11, D-20355, Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Heshmat Noei
- Centre for X-ray and Nanoscience (CXNS), Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
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Cheng C, Fang Q, Fernandez-Alberti S, Long R. Depleted Oxygen Defect State Enhancing Tungsten Trioxide Photocatalysis: A Quantum Dynamics Perspective. J Phys Chem Lett 2022; 13:5571-5580. [PMID: 35696649 DOI: 10.1021/acs.jpclett.2c01541] [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
Oxygen vacancies generally create midgap states in transition metal oxides, which are expected to decrease the photoelectrochemical water-splitting efficiency. Recent experiments defy this expectation but leave the mechanism unclear. Focusing on the photoanode WO3 as a prototypical system, we demonstrate using nonadiabatic molecular dynamics that an oxygen vacancy suppresses nonradiative electron-hole recombination, because the defect acts as an electron reservoir instead of a recombination center. The occupied midgap electrons prefer to be populated a priori compared to the band edge transition because of a larger transition dipole moment, converting to depleted/unoccupied trap states that rapidly accept conduction band electrons and then cause trap-assisted recombination by impeding the bandgap recombination regardless of oxygen vacancy configurations. The reported results provide a fundamental understanding of the "realistic" role of the oxygen vacancies and their influence on charge-phonon dynamics and carrier lifetime. The study generates valuable insights into the design of high-performance transition metal oxide photocatalysts.
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Affiliation(s)
- Cheng Cheng
- College of Chemistry, Key Laboratory of Theoretical & Computational Photochemistry of Ministry of Education, Beijing Normal University, Beijing 100875, China
| | - Qiu Fang
- College of Chemistry, Key Laboratory of Theoretical & Computational Photochemistry of Ministry of Education, Beijing Normal University, Beijing 100875, China
| | - S Fernandez-Alberti
- Departamento de Cienciay Tecnologia, Universidad Nacional de Quilmes/CONICET, B1876BXD Bernal, Argentina
| | - Run Long
- College of Chemistry, Key Laboratory of Theoretical & Computational Photochemistry of Ministry of Education, Beijing Normal University, Beijing 100875, China
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Tanner AJ, Thornton G. TiO 2 Polarons in the Time Domain: Implications for Photocatalysis. J Phys Chem Lett 2022; 13:559-566. [PMID: 35014263 PMCID: PMC9097515 DOI: 10.1021/acs.jpclett.1c03677] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 01/03/2022] [Indexed: 06/14/2023]
Abstract
Exploiting the availability of solar energy to produce valuable chemicals is imperative in our quest for a sustainable energy cycle. TiO2 has emerged as an efficient photocatalyst, and as such its photochemistry has been studied extensively. It is well-known that polaronic defect states impact the activity of this chemistry. As such, understanding the fundamental excitation mechanisms deserves the attention of the scientific community. However, isolating the contribution of polarons to these processes has required increasingly creative experimental techniques and expensive theory. In this Perspective, we discuss recent advances in this field, with a particular focus on two-photon photoemission spectroscopy (2PPE) and density functional theory (DFT), and discuss the implications for photocatalysis.
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6
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Khan R, Ali-Löytty H, Tukiainen A, Tkachenko NV. Comparison of the heat-treatment effect on carrier dynamics in TiO 2 thin films deposited by different methods. Phys Chem Chem Phys 2021; 23:17672-17682. [PMID: 34373878 DOI: 10.1039/d1cp02716f] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Polycrystalline titanium dioxide thin films are routinely used in a broad range of applications where charge carrier lifetime is essential for their performance but the effects of the fabrication method are rarely considered. Here we compare three popular deposition methods, atomic layer deposition (ALD), ion beam sputtering (IBS), and spray pyrolysis deposition (SPD). In all three cases, 30 nm thin films of TiO2 are prepared, and the as-deposited films show no defined crystal structure and can be classified as amorphous films. Heat treatment (HT) of the films converts all of them to polycrystalline anatase TiO2 as revealed by XRD measurements. A photophysical study was carried out by pico- to nano-second transient absorption pump-probe spectroscopy in transmittance and reflectance modes which allows taking into account the effects due to the photoinduced refractive index changes. This study shows that the HT increases the lifetime of the photo-carriers gradually to a nanosecond time domain (approx. 4 ns) as compared to a few picoseconds of the as-deposited samples. The photo-carrier dynamics of the samples become very similar after heat-treatment, though the topographical features and texture of the films observed with AFM and XRD are quite different. The measured transient absorption spectra of the samples also indicate that the photo-carrier relaxation pathway involves electron and hole trap states with the longest-lived being the hole traps. To evaluate the photoactivity of thin films, methylene blue (MB) photodegradation was tested for all the as-deposited and HT samples and the results showed a 20% higher degradation rate for the IBS HT sample due to the more textured surface.
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Affiliation(s)
- Ramsha Khan
- Photonic Compounds and Nanomaterials Group, Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 692, 33014 Tampere, Finland.
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7
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Tanner AJ, Kerr R, Fielding HH, Thornton G. Chemical Modification of Polaronic States in Anatase TiO 2(101). THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:14348-14355. [PMID: 34267854 PMCID: PMC8273885 DOI: 10.1021/acs.jpcc.1c03684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/24/2021] [Revised: 06/02/2021] [Indexed: 06/13/2023]
Abstract
Two polymorphs of TiO2, anatase and rutile, are employed in photocatalytic applications. It is broadly accepted that anatase is the more catalytically active and subsequently finds wider commercial use. In this work, we focus on the Ti3+ polaronic states of anatase TiO2(101), which lie at ∼1.0 eV binding energy and are known to increase catalytic performance. Using UV-photoemission and two-photon photoemission spectroscopies, we demonstrate the capability to tune the excited state resonance of polarons by controlling the chemical environment. Anatase TiO2(101) contains subsurface polarons which undergo sub-band-gap photoexcitation to states ∼2.0 eV above the Fermi level. Formic acid adsorption dramatically influences the polaronic states, increasing the binding energy by ∼0.3 eV. Moreover, the photoexcitation oscillator strength changes significantly, resonating with states ∼3.0 eV above the Fermi level. We show that this behavior is likely due to the surface migration of subsurface oxygen vacancies.
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Affiliation(s)
- Alex J. Tanner
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - Robin Kerr
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
| | - Helen H. Fielding
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
| | - Geoff Thornton
- Department
of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- London
Centre for Nanotechnology, University College
London, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
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8
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Zhang L, Chu W, Zhao C, Zheng Q, Prezhdo OV, Zhao J. Dynamics of Photoexcited Small Polarons in Transition-Metal Oxides. J Phys Chem Lett 2021; 12:2191-2198. [PMID: 33630612 DOI: 10.1021/acs.jpclett.1c00003] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The dynamics of photoexcited polarons in transition-metal oxides (TMOs), including their formation, migration, and quenching, plays an important role in photocatalysis and photovoltaics. Taking rutile TiO2 as a prototypical system, we use ab initio nonadiabatic molecular dynamics simulation to investigate the dynamics of small polarons induced by photoexcitation at different temperatures. The photoexcited electron is trapped by the distortion of the surrounding lattice and forms a small polaron within tens of femtoseconds. Polaron migration among Ti atoms is strongly correlated with quenching through an electron-hole (e-h) recombination process. At low temperature, the polaron is localized on a single Ti atom and polaron quenching occurs within several nanoseconds. At increased temperature, as under solar cell operating conditions, thermal phonon excitation stimulates the hopping and delocalization of polarons, which induces fast polaron quenching through the e-h recombination within 200 ps. Our study proves that e-h recombination centers can be formed by photoexcited polarons, which provides new insights to understand the efficiency bottleneck of photocatalysis and photovoltaics in TMOs.
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Affiliation(s)
- Lili Zhang
- Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China
| | - Weibin Chu
- Departments of Chemistry, and Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | | | | | - Oleg V Prezhdo
- Departments of Chemistry, and Physics and Astronomy, University of Southern California, Los Angeles, California 90089, United States
| | - Jin Zhao
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh Pennsylvania 15260, United States
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Dai B, Chen Y, Hao SM, Huang H, Kou J, Lu C, Lin Z, Xu Z. Sustainable Internal Electric Field for Enhanced Photocatalysis: From Material Design to Energy Utilization. J Phys Chem Lett 2020; 11:7407-7416. [PMID: 32794709 DOI: 10.1021/acs.jpclett.0c00889] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The intrinsic internal electric field in a ferroelectric photocatalyst is beneficial for improving the photocatalytic properties because of its positive effect on the separation and migration of photogenerated carriers. However, this kind of internal electric field is static and easily saturated by inner and outer shielding effects, seriously restricting its potential in photocatalysis. To overcome this problem, a sustainable internal electric field was introduced into photocatalysis based on piezoelectric and pyroelectric effect, which exhibits good capability in consistently boosting photocatalytic activity, thus becoming a hot research topic. In this Perspective we summarize the recent significant progress in the construction of sustainable internal electric fields for facilitating photocatalysis from material design to energy utilization. Moreover, the fascinating influence of sustainable internal electric fields on carrier behavior is also discussed. Finally, a summary and outlook for building a sustainable internal electric field to further enhance photocatalytic performance are provided.
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Affiliation(s)
- Baoying Dai
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, P.R. China
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Yukai Chen
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, P.R. China
| | - Shu-Meng Hao
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Hengming Huang
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, P.R. China
| | - Jiahui Kou
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, P.R. China
| | - Chunhua Lu
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, P.R. China
| | - Zhiqun Lin
- School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Zhongzi Xu
- State Key Laboratory of Materials-Oriented Chemical Engineering, College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 210009, P.R. China
- Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, P.R. China
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