1
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Li J, Ji Q, Wang R, Zhang ZG, Wang X, Xiao M, Lu YQ, Zhang C. Charge Generation Dynamics in Organic Photovoltaic Blends under One-Sun-Equivalent Illumination Detected by Highly Sensitive Terahertz Spectroscopy. J Am Chem Soc 2024; 146:20312-20322. [PMID: 38980945 DOI: 10.1021/jacs.4c05786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/11/2024]
Abstract
Organic photovoltaic (OPV) devices attain high performance with nonfullerene acceptors by utilizing the synergistic dual channels of charge generation that originate from excitations in both the donor and acceptor materials. However, the specific intermediate states that facilitate both channels are subject to debate. To address this issue, we employ time-resolved terahertz spectroscopy with improved sensitivity (ΔE/E < 10-6), enabling direct probing of charge generation dynamics in a prototypical PM6:Y6 bulk heterojunction system under one-sun-equivalent excitation density. Charge generation arising from donor excitations is characterized with a rise time of ∼9 ps, while that from acceptor excitations shows a rise time of ∼18 ps. Temperature-dependent measurements further reveal notably distinct activation energies for these two charge generation pathways. Additionally, the two channels of charge generation can be substantially manipulated by altering the ratio of bulk to interfaces. These findings strongly suggest the presence of two distinct intermediate states: interfacial and intramoiety excitations. These states are crucial in mediating the transfer of electrons and holes, driving charge generation within OPV devices.
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Affiliation(s)
- Jiacong Li
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Qing Ji
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Rui Wang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
- College of Physics, Nanjing University of Aeronautics and Astronautics, and Key Laboratory of Aerospace Information Materials and Physics (NUAA), MIIT, Nanjing 211106, China
- Institute of Materials Engineering, Nanjing University, Nantong, Jiangsu 226019, China
| | - Zhi-Guo Zhang
- State Key Laboratory of Organic/Inorganic Composites, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China
| | - Xiaoyong Wang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Min Xiao
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States
| | - Yan-Qing Lu
- National Laboratory of Solid State Microstructures, Key Laboratory of Intelligent Optical Sensing and Manipulation, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210023, China
| | - Chunfeng Zhang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
- Institute of Materials Engineering, Nanjing University, Nantong, Jiangsu 226019, China
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2
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Citty B, Lynd JK, Gera T, Varvelo L, Raccah DIGB. MesoHOPS: Size-invariant scaling calculations of multi-excitation open quantum systems. J Chem Phys 2024; 160:144118. [PMID: 38619062 DOI: 10.1063/5.0197825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Accepted: 03/11/2024] [Indexed: 04/16/2024] Open
Abstract
The photoexcitation dynamics of molecular materials on the 10-100 nm length scale depend on complex interactions between electronic and vibrational degrees of freedom, rendering exact calculations difficult or intractable. The adaptive Hierarchy of Pure States (adHOPS) is a formally exact method that leverages the locality imposed by interactions between thermal environments and electronic excitations to achieve size-invariant scaling calculations for single-excitation processes in systems described by a Frenkel-Holstein Hamiltonian. Here, we extend adHOPS to account for arbitrary couplings between thermal environments and vertical excitation energies, enabling formally exact, size-invariant calculations that involve multiple excitations or states with shared thermal environments. In addition, we introduce a low-temperature correction and an effective integration of the noise to reduce the computational expense of including ultrafast vibrational relaxation in Hierarchy of Pure States (HOPS) simulations. We present these advances in the latest version of the open-source MesoHOPS library and use MesoHOPS to characterize charge separation at a one-dimensional organic heterojunction when both the electron and hole are mobile.
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Affiliation(s)
- Brian Citty
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Jacob K Lynd
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Tarun Gera
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Leonel Varvelo
- Department of Chemistry, Southern Methodist University, PO Box 750314 Dallas, Texas 75205, USA
| | - Doran I G B Raccah
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
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3
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Liu L, Yan Y, Zhao S, Wang T, Zhang W, Zhang J, Hao X, Zhang Y, Zhang X, Wei Z. Stereoisomeric Non-Fullerene Acceptors-Based Organic Solar Cells. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2305638. [PMID: 37699757 DOI: 10.1002/smll.202305638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 08/20/2023] [Indexed: 09/14/2023]
Abstract
Chiral alkyl chains are ubiquitously observed in organic semiconductor materials and can regulate solution processability and active layer morphology, but the effect of stereoisomers on photovoltaic performance has rarely been investigated. For the racemic Y-type acceptors widely used in organic solar cells, it remains unknown if the individual chiral molecules separate into the conglomerate phase or if racemic phase prevails. Here, the photovoltaic performance of enantiomerically pure Y6 derivatives, (S,S)/(R,R)-BTP-4F, and their chiral mixtures are compared. It is found that (S,S) and (R,R)-BTP-4F molecule in the racemic mixtures tends to interact with its enantiomer. The racemic mixtures enable efficient light harvesting, fast hole transfer, and long polaron lifetime, which is conducive to charge generation and suppresses the recombination losses. Moreover, abundant charge diffusion pathways provided by the racemate contribute to efficient charge transport. As a result, the racemate system maximizes the power output and minimizes losses, leading to a higher efficiency of 18.16% and a reduced energy loss of 0.549 eV, as compared to the enantiomerically pure molecules. This study demonstrates that the chirality of non-fullerene acceptors should receive more attention and be designed rationally to enhance the efficiency of organic solar cells.
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Affiliation(s)
- Lixuan Liu
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing, 100190, China
- School of Future Technology, University of Chinese Academy of Sciences (UCAS), Beijing, 100049, China
| | - Yangjun Yan
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing, 100190, China
- School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Shengda Zhao
- School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Tong Wang
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Wenqing Zhang
- School of Physics, State Key Laboratory of Crystal Material, Shandong University, Jinan, 250100, China
| | - Jianqi Zhang
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Xiaotao Hao
- School of Physics, State Key Laboratory of Crystal Material, Shandong University, Jinan, 250100, China
| | - Yajie Zhang
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Xinghua Zhang
- School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Zhixiang Wei
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing, 100190, China
- School of Future Technology, University of Chinese Academy of Sciences (UCAS), Beijing, 100049, China
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4
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Montanaro A, Park KH, Fassioli F, Giusti F, Fausti D, Scholes GD. Manipulation of Charge Delocalization in a Bulk Heterojunction Material Using a Mid-Infrared Push Pulse. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2023; 127:13712-13722. [PMID: 37492193 PMCID: PMC10364132 DOI: 10.1021/acs.jpcc.3c02938] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 06/07/2023] [Indexed: 07/27/2023]
Abstract
In organic bulk heterojunction materials, charge delocalization has been proposed to play a vital role in the generation of free carriers by effectively reducing the Coulomb attraction via an interfacial charge transfer exciton (CTX). Pump-push-probe (PPP) experiments produced evidence that the excess energy given by a push pulse enhances delocalization, thereby increasing photocurrent. However, previous studies have employed near-infrared push pulses in the range ∼0.4-0.6 eV, which is larger than the binding energy of a typical CTX. This raises the doubt that the push pulse may directly promote dissociation without involving delocalized states. Here, we perform PPP experiments with mid-infrared push pulses at energies that are well below the binding energy of a CTX state (0.12-0.25 eV). We identify three types of CTXs: delocalized, localized, and trapped. The excitation resides over multiple polymer chains in delocalized CTXs, while it is restricted to a single chain (albeit maintaining a degree of intrachain delocalization) in localized CTXs. Trapped CTXs are instead completely localized. The pump pulse generates a "hot" delocalized CTX, which promptly relaxes to a localized CTX and eventually to trapped states. We find that photo-exciting localized CTXs with push pulses resonant to the mid-infrared charge transfer absorption can promote delocalization and, in turn, contribute to the formation of long-lived charge separated states. On the other hand, we found that trapped CTXs are non-responsive to the push pulses. We hypothesize that delocalized states identified in prior studies are only accessible in systems where there is significant interchain electronic coupling or regioregularity that supports either inter- or intrachain polaron delocalization. This, in turn, emphasizes the importance of engineering the micromorphology and energetics of the donor-acceptor interface to exploit the full potential of a material for photovoltaic applications.
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Affiliation(s)
- Angela Montanaro
- Department of Physics, University of Trieste, Via A. Valerio 2, 34127 Trieste, Italy
- Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163.5 in AREA Science Park,
Basovizza, 34149 Trieste, Italy
- Department
of Physics, University of Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Kyu Hyung Park
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Francesca Fassioli
- Department
of Physics, University of Erlangen-Nürnberg, 91058 Erlangen, Germany
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- SISSA − Scuola Internazionale Superiore di Studi Avanzati, Trieste 34136, Italy
| | - Francesca Giusti
- Department of Physics, University of Trieste, Via A. Valerio 2, 34127 Trieste, Italy
- Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163.5 in AREA Science Park,
Basovizza, 34149 Trieste, Italy
| | - Daniele Fausti
- Department of Physics, University of Trieste, Via A. Valerio 2, 34127 Trieste, Italy
- Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163.5 in AREA Science Park,
Basovizza, 34149 Trieste, Italy
- Department
of Physics, University of Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Gregory D. Scholes
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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5
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Bai L, Wang J, Yang K, Yan Y, Jin M, Cui D, Zhao M. Cobalt-doped double-layer α-Fe 2O 3 nanorod arrays for enhanced photoelectrochemical reduction of Cr(VI). NANOSCALE RESEARCH LETTERS 2023; 18:10. [PMID: 36764982 DOI: 10.1186/s11671-023-03785-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Accepted: 01/31/2023] [Indexed: 05/24/2023]
Abstract
Element doping is an important method for improving the performance levels of photoelectrochemical (PEC) cells. Nevertheless, to date, the PEC conversion efficiency and photocurrent characteristics of the available photoanodes remain very low. In this study, cobalt (Co) was selectively doped into the bottom and/or top layers of double-layered α-Fe2O3 nanorod arrays grown on conductive transparent substrates (F:SnO2, FTO) via a two-step hydrothermal method; this process was performed to enhance the charge transfer ability and thus significantly improve the PEC performance. The light response capabilities of all α-Fe2O3 films were evaluated by an electrochemical workstation under dark or visible light irradiation conditions. The sample of Co doped in the bottom layer exhibited a high photoelectrochemical performance, achieving a current density of 1.37 mA/cm2 at + 1.0 V versus saturated calomel electrode (SCE); additionally, the sample exhibited a photoelectric synergistic ability to reduce Cr(VI) in an aqueous solution, with 84.85% reduction in 180 min. Under the influence of the electric field inside the double-layer electrode, the photoexcited electrons and holes are transferred to the surfaces of the FTO substrate and the photoanode, increasing the current density and enhancing Cr(VI) reduction. The results of this study offer an alternative approach for designing novel photoanodes with improved PEC performance levels by engineering the electron density distribution and band structure for efficient carrier separation; the results may provide new solutions in heavy metal reduction and contaminant degradation projects.
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Affiliation(s)
- Long Bai
- College of Life Science, Northeast Forestry University, Harbin, China
| | - Jueyu Wang
- College of Life Science, Northeast Forestry University, Harbin, China
| | - Kuo Yang
- College of Life Science, Northeast Forestry University, Harbin, China
| | - Yi Yan
- College of Life Science, Northeast Forestry University, Harbin, China
| | - Meitong Jin
- College of Life Science, Northeast Forestry University, Harbin, China
| | - Daizong Cui
- College of Life Science, Northeast Forestry University, Harbin, China.
| | - Min Zhao
- College of Life Science, Northeast Forestry University, Harbin, China.
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6
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Yan Y, Zhang Y, Memon WA, Wang M, Zhang X, Wei Z. The role of entropy gains in the exciton separation in organic solar cells. Macromol Rapid Commun 2022; 43:e2100903. [PMID: 35338684 DOI: 10.1002/marc.202100903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 02/16/2022] [Indexed: 11/06/2022]
Abstract
In organic solar cell (OSC), the lower dielectric constant of organic semiconductor material induces a strong Coulomb attraction between electron-hole pairs, which leads to a low exciton separation efficiency, especially the charge transfer (CT) state. The CT state formed at the electron-donor (D) and electron-acceptor (A) interface is regarded as an unfavorable property of organic photovoltaic devices. Since the OSC works in a nonzero temperature condition, the entropy effect would be one of the main reasons to overcome the Coulomb energy barrier and must be taken into account. In this review, we review the present understanding of the entropy-driven charge separation and describe how factors such as the dimensionality of the organic semiconductor, energy disorder effect, the morphology of the active layer, and the nonequilibrium effect affect the entropy contribution in compensating the Coulomb dissociation barrier for CT exciton separation and charge generation process. We focus on the investigation of the entropy effect on exciton dissociation mechanism from both theoretical and experimental aspects, which provides pathways for understanding the underlying mechanisms of exciton separation and further enhancing the efficiency of OSCs. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Yangjun Yan
- School of Science, Beijing Jiaotong University, Beijing, 100044, China.,CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Yajie Zhang
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Waqar Ali Memon
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Mengni Wang
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Xinghua Zhang
- School of Science, Beijing Jiaotong University, Beijing, 100044, China
| | - Zhixiang Wei
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
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7
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Carr JM, Allen TG, Larson BW, Davydenko IG, Dasari RR, Barlow S, Marder SR, Reid OG, Rumbles G. Short and long-range electron transfer compete to determine free-charge yield in organic semiconductors. MATERIALS HORIZONS 2022; 9:312-324. [PMID: 34787147 DOI: 10.1039/d1mh01331a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Understanding how Frenkel excitons efficiently split to form free-charges in low-dielectric constant organic semiconductors has proven challenging, with many different models proposed in recent years to explain this phenomenon. Here, we present evidence that a simple model invoking a modest amount of charge delocalization, a sum over the available microstates, and the Marcus rate constant for electron transfer can explain many seemingly contradictory phenomena reported in the literature. We use an electron-accepting fullerene host matrix dilutely sensitized with a series of electron donor molecules to test this hypothesis. The donor series enables us to tune the driving force for photoinduced electron transfer over a range of 0.7 eV, mapping out normal, optimal, and inverted regimes for free-charge generation efficiency, as measured by time-resolved microwave conductivity. However, the photoluminescence of the donor is rapidly quenched as the driving force increases, with no evidence for inverted behavior, nor the linear relationship between photoluminescence quenching and charge-generation efficiency one would expect in the absence of additional competing loss pathways. This behavior is self-consistently explained by competitive formation of bound charge-transfer states and long-range or delocalized free-charge states, where both rate constants are described by the Marcus rate equation. Moreover, the model predicts a suppression of the inverted regime for high-concentration blends and efficient ultrafast free-charge generation, providing a mechanistic explanation for why Marcus-inverted-behavior is rarely observed in device studies.
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Affiliation(s)
- Joshua M Carr
- University of Colorado Boulder, Materials Science & Engineering Program, Boulder, CO, 80303, USA
| | - Taylor G Allen
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, CO, 80401, USA.
| | - Bryon W Larson
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, CO, 80401, USA.
| | - Iryna G Davydenko
- Georgia Institute of Technology, School of Chemistry and Biochemistry, Atlanta, GA, 30332, USA
| | - Raghunath R Dasari
- Georgia Institute of Technology, School of Chemistry and Biochemistry, Atlanta, GA, 30332, USA
| | - Stephen Barlow
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, CO, 80401, USA.
- Georgia Institute of Technology, School of Chemistry and Biochemistry, Atlanta, GA, 30332, USA
- University of Colorado Boulder, Renewable and Sustainable Energy Institute, Boulder, CO, 80303, USA
| | - Seth R Marder
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, CO, 80401, USA.
- Georgia Institute of Technology, School of Chemistry and Biochemistry, Atlanta, GA, 30332, USA
- University of Colorado Boulder, Renewable and Sustainable Energy Institute, Boulder, CO, 80303, USA
- University of Colorado Boulder, Department of Chemistry, Boulder, CO, 80303, USA
- University of Colorado Boulder, Department of Chemical and Biological Engineering, Boulder, CO, 80303, USA
| | - Obadiah G Reid
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, CO, 80401, USA.
- University of Colorado Boulder, Renewable and Sustainable Energy Institute, Boulder, CO, 80303, USA
| | - Garry Rumbles
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, CO, 80401, USA.
- University of Colorado Boulder, Renewable and Sustainable Energy Institute, Boulder, CO, 80303, USA
- University of Colorado Boulder, Department of Chemistry, Boulder, CO, 80303, USA
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8
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Huang Y, Zhang L, Hao Y. Why ultrafast charge separation occurs in bulk-heterojunction organic solar cells: a multichain tight binding model study. Phys Chem Chem Phys 2021; 23:22685-22691. [PMID: 34604887 DOI: 10.1039/d1cp03686f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Bulk-heterojunction (BHJ) organic solar cells (OSCs) exhibit ultrafast charge separation (UCS) which enables lower geminate charge recombination and high internal quantum efficiency. Unravelling why UCS occurs in BHJ-OSCs is important for the exploration of devices in future, however it is still far from clear. In this work, we build a multichain tight-binding model to study the conditions for realizing UCS. We propose that two conditions are important: (i) the BHJ-OSC has a morphology with donor and acceptor molecules being individually aggregated; (ii) the ratio of the donor/acceptor interfacial coupling to the internal donor/donor and acceptor/acceptor coupling should be smaller than a threshold. In addition, we suggest that increasing the donor/acceptor energetic offset will boost the UCS efficiency. As a fundamental theoretical analysis on the underlying mechanism of UCS, our work provides design rules for optimizing high-performance BHJ OSCs.
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Affiliation(s)
- Yujuan Huang
- College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, 030024, China.
| | - Longlong Zhang
- College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, 030024, China.
| | - Yuying Hao
- College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan, 030024, China.
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9
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He S, Han Y, Guo J, Wu K. Entropy-Gated Thermally Activated Delayed Emission Lifetime in Phenanthrene-Functionalized CsPbBr 3 Perovskite Nanocrystals. J Phys Chem Lett 2021; 12:8598-8604. [PMID: 34468154 DOI: 10.1021/acs.jpclett.1c02547] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Charge and electronic energy transfer form the basis of many natural and artificial energy transduction systems. The energy landscapes that drive these transfer processes are often constructed from enthalpy changes. In contrast, the entropic effect, although occasionally invoked to explain some excited-state dynamics, has rarely been used to actively control charge/energy flow. Here we derive a generic formula describing how entropy can quantitatively gate the thermally activated delayed emission lifetime in semiconductor nanocrystal-molecular triplet acceptor complexes and experimentally verify the model using highly emissive, quantum-confined CsPbBr3 nanocrystals surface-functionalized with multiple phenanthrene triplet acceptors. Triplet energy transfer from photoexcited CsPbBr3 nanocrystals to phenanthrene is followed by thermally activated repopulation of nanocrystal excitons, leading to delayed nanocrystal emission. The lifetime of delayed emission increases with the phenanthrene/nanocrystal ratio, due to lowering of the free energy of the acceptor state by entropic gain. This study points toward a direction of using entropy to artificially design donor-acceptor light-emitting materials with predetermined excited-state lifetimes.
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Affiliation(s)
- Shan He
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Yaoyao Han
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jingwei Guo
- Key Laboratory of Chemical Lasers, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Kaifeng Wu
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
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10
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Varvelo L, Lynd JK, Bennett DIG. Formally exact simulations of mesoscale exciton dynamics in molecular materials. Chem Sci 2021; 12:9704-9711. [PMID: 34349941 PMCID: PMC8293828 DOI: 10.1039/d1sc01448j] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 05/31/2021] [Indexed: 02/04/2023] Open
Abstract
Excited state carriers, such as excitons, can diffuse on the 100 nm to micron length scale in molecular materials but only delocalize over short length scales due to coupling between electronic and vibrational degrees-of-freedom. Here, we leverage the locality of excitons to adaptively solve the hierarchy of pure states equations (HOPS). We demonstrate that our adaptive HOPS (adHOPS) methodology provides a formally exact and size-invariant (i.e., ) scaling algorithm for simulating mesoscale quantum dynamics. Finally, we provide proof-of-principle calculations for exciton diffusion on linear chains containing up to 1000 molecules. The adaptive hierarchy of pure states (adHOPS) algorithm leverages the locality of excitons in molecular materials to perform formally-exact simulations with size-invariant (i.e., ) scaling, enabling efficient simulations of mesoscale exciton dynamics.![]()
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Affiliation(s)
- Leonel Varvelo
- Department of Chemistry, Southern Methodist University PO Box 750314 Dallas TX USA
| | - Jacob K Lynd
- Department of Chemistry, Southern Methodist University PO Box 750314 Dallas TX USA
| | - Doran I G Bennett
- Department of Chemistry, Southern Methodist University PO Box 750314 Dallas TX USA
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11
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Feng S, Wang YC, Liang W, Zhao Y. Vibrationally Resolved Absorption Spectra and Exciton Dynamics in Zinc Phthalocyanine Aggregates: Effects of Aggregation Lengths and Remote Exciton Transfer. J Phys Chem A 2021; 125:2932-2943. [PMID: 33822626 DOI: 10.1021/acs.jpca.1c01271] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The vibrationally resolved absorption spectra and exciton dynamics in the α-zinc phthalocyanine aggregates are theoretically investigated by using a non-Markovian stochastic Schrödinger equation. The model Hamiltonian adopted for spectral and dynamic simulations explicitly includes the couplings for both nearest-neighbor and remote exciton transfer, and it is parametrized from first-principles calculations. The results indicate that aggregation lengths and remote exciton transfer significantly influence the relative energy alignment between delocalized Frenkel exciton (FE) and charge transfer (CT) states, which in turn strongly affects the relative intensities of the two absorption peaks in the Q-band region. Analytical formulas are derived to establish quantitative structure-spectra relationships in aggregates, and they offer simple patterns to extract electronic-state properties directly from absorption spectra. The dynamics simulations reveal that the light absorption can directly generate mixed states with both FE and CT features, but it is hard for the photoexcitation from the Q-band region to generate free carriers due to the high energies of charge-separated states.
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Affiliation(s)
- Shishi Feng
- State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Yu-Chen Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - WanZhen Liang
- State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
| | - Yi Zhao
- State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China
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12
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Xu Y, Yao H, Ma L, Wang J, Hou J. Efficient charge generation at low energy losses in organic solar cells: a key issues review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2020; 83:082601. [PMID: 32375132 DOI: 10.1088/1361-6633/ab90cf] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Light absorption generates strongly bound excitons in organic solar cells (OSCs). To obtain efficient charge generation, a large driving force is required, which causes a large energy loss (E loss) and severely hinders the improvement in the power conversion efficiencies (PCEs) of OSCs. Recently, the development of non-fullerene OSCs has seen great success, and the resulting OSCs can yield highly efficient charge generation with a negligible driving force, which raises a fundamental question about how the excitons split into free charges. From a chemical structure perspective, the molecular electrostatic potential differences between donors and acceptors may play a critical role in facilitating charge separation. Although the E loss caused by charge generation has been suppressed, charge recombination, particularly via non-radiative pathways, severely limits further improvements in the PCEs. In OSCs with negligible driving forces, the lowest excited state, a hybrid local exciton-charge transfer state, is believed to have a strong association with the non-radiative E loss. This review discusses the efficient charge generation at low E loss values in highly efficient OSCs and highlights the issues that should be tackled to further improve the PCEs to new levels (∼20%).
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Affiliation(s)
- Ye Xu
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Polymer Physics and Chemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China. University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
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13
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Wang R, Zhang C, Li Q, Zhang Z, Wang X, Xiao M. Charge Separation from an Intra-Moiety Intermediate State in the High-Performance PM6:Y6 Organic Photovoltaic Blend. J Am Chem Soc 2020; 142:12751-12759. [DOI: 10.1021/jacs.0c04890] [Citation(s) in RCA: 122] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Rui Wang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Chunfeng Zhang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Qian Li
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Zhiguo Zhang
- College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China
| | - Xiaoyong Wang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Min Xiao
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States
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14
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Felekidis N, Melianas A, Kemerink M. The Role of Delocalization and Excess Energy in the Quantum Efficiency of Organic Solar Cells and the Validity of Optical Reciprocity Relations. J Phys Chem Lett 2020; 11:3563-3570. [PMID: 32301322 DOI: 10.1021/acs.jpclett.0c00945] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The photon energy dependence of long-range charge separation is studied for two prototypical polymer:fullerene systems. The internal quantum efficiency (IQE) of PCDTBT:PC61BM is experimentally shown to be independent of the excitation energy. In contrast, for TQ1:PC71BM the IQE is strongly energy-dependent for excitation energies close to charge transfer (CT) electroluminescence peak maximum while it becomes energy-independent at higher excitation energies. Kinetic Monte Carlo simulations reproduce the experimental IQE and reveal that the photon energy-dependence of the IQE is governed by charge delocalization. Efficient long-range separation at excitation energies corresponding to the CT electroluminescence peak maximum or lower requires an initial separation of the hole-electron pair by ∼4-5 nm, whereas delocalization is less important for charge separation at higher photon energies. Our modeling results suggest that a phenomenological reciprocity between CT electroluminescence and external quantum efficiency does not necessarily prove that commonly employed reciprocity relations between these spectra are valid from a fundamental perspective.
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Affiliation(s)
- N Felekidis
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - A Melianas
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
| | - M Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
- Centre for Advanced Materials, University of Heidelberg, 69120 Heidelberg, Germany
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15
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Tu Z, Han G, Yi Y. Barrier-Free Charge Separation Enabled by Electronic Polarization in High-Efficiency Non-fullerene Organic Solar Cells. J Phys Chem Lett 2020; 11:2585-2591. [PMID: 32163716 DOI: 10.1021/acs.jpclett.0c00405] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The separation of charge-transfer states into free charges at the donor/acceptor (D/A) interfaces plays a central role in organic solar cells (OSCs). Because of strong Coulomb attraction, the separation mechanisms are elusive, particularly for the high-efficiency non-fullerene (NF) OSCs with low exciton-dissociation driving forces. Here, we demonstrate that the Coulomb barriers can be substantially overcome by electronic polarization for OSCs based on a series of A-D-A acceptors (ITIC, IT-4F, and Y6). In contrast to fullerene-based D/A heterojunctions, the polarization energies for both donor holes and acceptor electrons are remarkably increased from the interfaces to pure regions in the NF heterojunctions because of strong stabilization on electrons but destabilization on holes by electrostatic interactions in the A-D-A acceptors. In particular, upon incorporation of fluorine substituents and electron-poor cores into ITIC, the increased polarization energies can completely compensate for the Coulomb attraction in the IT-4F- and Y6-based heterojunctions, leading to barrierless charge separation.
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Affiliation(s)
- Zeyi Tu
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy Sciences, Beijing 100049, China
| | - Guangchao Han
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Yuanping Yi
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy Sciences, Beijing 100049, China
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16
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Niu MS, Wang KW, Yang XY, Bi PQ, Zhang KN, Feng XJ, Chen F, Qin W, Xia JL, Hao XT. Hole Transfer Originating from Weakly Bound Exciton Dissociation in Acceptor-Donor-Acceptor Nonfullerene Organic Solar Cells. J Phys Chem Lett 2019; 10:7100-7106. [PMID: 31682127 DOI: 10.1021/acs.jpclett.9b02837] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The underlying hole-transfer mechanism in high-efficiency OSC bulk heterojunctions based on acceptor-donor-acceptor (A-D-A) nonfullerene acceptors (NFAs) remains unclear. Herein, we study the hole-transfer process between copolymer donor J91 and five A-D-A NFAs with different highest occupied molecular orbital energy offsets (ΔEH) (0.05-0.42 eV) via ultrafast optical spectroscopies. Transient absorption spectra reveal a rapid hole-transfer rate with small ΔEH, suggesting that a large energy offset is not required to overcome the exciton binding energy. Capacitance-frequency spectra and time-resolved photoluminescence spectra confirm the delocalization of an A-D-A-structured acceptor exciton with weak binding energy. Relative to the hole-transfer rate, hole-transfer efficiency is the key factor affecting device performance. We propose that holes primarily stem from weakly bound acceptor exciton dissociation, revealing a new insight into the hole-transfer process in A-D-A NFA-based OSCs.
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Affiliation(s)
- Meng-Si Niu
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Kang-Wei Wang
- School of Chemistry, Chemical Engineering and Life Science, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , 430070 Wuhan , Hubei , China
| | - Xiao-Yu Yang
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Peng-Qing Bi
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Kang-Ning Zhang
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Xian-Jin Feng
- School of Microelectronics , Shandong University , 250100 Jinan , Shandong , China
| | - Fei Chen
- Department of Mechanical, Materials and Manufacturing Engineering , The University of Nottingham Ningbo China , Ningbo 315100 , P.R. China
| | - Wei Qin
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
| | - Jian-Long Xia
- School of Chemistry, Chemical Engineering and Life Science, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing , Wuhan University of Technology , 430070 Wuhan , Hubei , China
| | - Xiao-Tao Hao
- School of Physics, State Key Laboratory of Crystal Materials , Shandong University , 250100 Jinan , Shandong , China
- ARC Centre of Excellence in Exciton Science, School of Chemistry , The University of Melbourne , Parkville , Victoria 3010 , Australia
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17
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Zhang YF, Zhang CZ. Experimental and theoretical study on spontaneous intermolecular charge transfer features and antiaromaticities of unusual bisazo compounds with antiaromatic cores. J Mol Struct 2019. [DOI: 10.1016/j.molstruc.2019.04.044] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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18
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Kohler B. Ultrafast photoinduced energy and charge transfer: concluding remarks. Faraday Discuss 2019; 216:564-573. [PMID: 31241093 DOI: 10.1039/c9fd90030f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The ability to characterize and control the energy and charge transfer events triggered by the photoexcitation of molecules and materials is of fundamental importance to many fields, including the sustainable capture and conversion of solar energy. This article summarizes the papers that were presented and discussed at the recent Faraday discussion meeting on ultrafast photoinduced energy and charge transfer. Ultrafast laser spectroscopy and theory were at the center of discussions on photoinduced phenomena in biological and nanoscale systems of interacting absorbers. Many of the questions that motivate this field of science have occupied scientists for many decades, as a look back to a Faraday discussion meeting that took place 60 years earlier reveals.
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Affiliation(s)
- Bern Kohler
- Department of Chemistry and Biochemistry, The Ohio State University, 100W. 18th Ave., Columbus, OH 43210, USA.
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19
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Kafle TR, Kattel B, Yao P, Zereshki P, Zhao H, Chan WL. Effect of the Interfacial Energy Landscape on Photoinduced Charge Generation at the ZnPc/MoS 2 Interface. J Am Chem Soc 2019; 141:11328-11336. [PMID: 31259543 DOI: 10.1021/jacs.9b05893] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Monolayer transition-metal dichalcogenide crystals (TMDC) can be combined with other functional materials, such as organic molecules, to form a wide range of heterostructures with tailorable properties. Although a number of works have shown that ultrafast charge transfer (CT) can occur at organic/TMDC interfaces, conditions that would facilitate the separation of interfacial CT excitons into free carriers remain unclear. Here, time-resolved and steady-state photoemission spectroscopy are used to study the potential energy landscape, charge transfer, and exciton dynamics at the zinc phthalocyanine (ZnPc)/monolayer (ML) MoS2 and ZnPc/bulk MoS2 interfaces. Surprisingly, although both interfaces have a type-II band alignment and exhibit sub-100 fs CT, the CT excitons formed at the two interfaces show drastically different evolution dynamics. The ZnPc/ML-MoS2 behaves like typical donor-acceptor interfaces in which CT excitons dissociate into electron-hole pairs. On the contrary, back electron transfer occur at ZnPc/bulk-MoS2, which results in the formation of triplet excitons in ZnPc. The difference can be explained by the different amount of band bending found in the ZnPc film deposited on ML-MoS2 and bulk-MoS2. Our work illustrates that the potential energy landscape near the interface plays an important role in the charge separation behavior. Therefore, considering the energy level alignment at the interface alone is not enough for predicting whether free charges can be generated effectively from an interface.
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Affiliation(s)
- Tika R Kafle
- Department of Physics and Astronomy , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Bhupal Kattel
- Department of Physics and Astronomy , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Peng Yao
- Department of Physics and Astronomy , University of Kansas , Lawrence , Kansas 66045 , United States.,Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology , Beijing Jiaotong University , Beijing 100044 , China
| | - Peymon Zereshki
- Department of Physics and Astronomy , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Hui Zhao
- Department of Physics and Astronomy , University of Kansas , Lawrence , Kansas 66045 , United States
| | - Wai-Lun Chan
- Department of Physics and Astronomy , University of Kansas , Lawrence , Kansas 66045 , United States
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20
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Melianas A, Kemerink M. Photogenerated Charge Transport in Organic Electronic Materials: Experiments Confirmed by Simulations. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1806004. [PMID: 30719756 DOI: 10.1002/adma.201806004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2018] [Revised: 10/29/2018] [Indexed: 06/09/2023]
Abstract
The performance of organic optoelectronic devices, such as organic photovoltaic (OPV) cells, is to a large extent dictated by their ability to transport the photogenerated charge, with relevant processes spanning a wide temporal (fs-µs) and spatial (1-100 nm) range. However, time-resolved techniques can access only a limited temporal window, and often contradict steady-state measurements. Here, commonly employed steady-state and time-resolved techniques are unified over an exceptionally wide temporal range (fs-µs) in a consistent physical picture. Experimental evidence confirmed by numerical simulations shows that, although various techniques probe different time scales, they are mutually consistent as they probe the same physical mechanisms governing charge motion in disordered media-carrier hopping and thermalization in a disorder-broadened density of states (DOS). The generality of this framework is highlighted by time-resolved experimental data obtained on polymer:fullerene, polymer:polymer, and small-molecule blends with varying morphology, including recent experiments revealing that low donor content OPV devices operate by long-range hole tunneling between non-nearest-neighbor molecules. The importance of nonequilibrium processes in organic electronic materials is reviewed, with a particular focus on experimental data and understanding charge transport physics in terms of material DOS.
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Affiliation(s)
- Armantas Melianas
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Martijn Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183, Linköping, Sweden
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21
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Huang J, Mo Y, Yao Y. Charge-transfer state dynamics in all-polymer solar cells: formation, dissociation and decoherence. Phys Chem Chem Phys 2019; 21:2755-2763. [PMID: 30666324 DOI: 10.1039/c8cp06467a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
All-polymer solar cells have made substantial achievements in recent years, offering numerous unsettled subjects for mechanical researchers. In order to quantitatively study the influence of the molecular electrostatic potential on the charge generation proposed by the experimenter, we simulate the ultrafast dynamics of the charge-transfer (CT) state at the interface between two polymer chains, which are respectively regarded as the donor and acceptor in all-polymer solar cells. The formation of a stable CT state is found to be sensitive to the distance between two oppositely charged polarons and the relevant critical electrostatic potential is thus quantified, which is in good agreement with experiments. In order to get insight into the dependence of the dissociation of the CT state on the width of the interfacial layer, two quantities are calculated: one is the Coulomb capture radius between the two polarons and the other is the quantum trace distance which serves as the fingerprint of the quantum coherence between them. The dissociation of the CT state is found to take place within an ultrafast timescale for an optimum interfacial width. The classical spatial distance and the quantum trace distance manifest a converging trend, suggesting a decoherence scenario for the charge separation in all-polymer solar cells.
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Affiliation(s)
- Jiaqing Huang
- Department of Physics and State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China.
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22
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Bombile JH, Janik MJ, Milner ST. Energetics of exciton binding and dissociation in polythiophenes: a tight binding approach. Phys Chem Chem Phys 2019; 21:11999-12011. [DOI: 10.1039/c9cp01116a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A tight-binding exciton model that describes the continuum from the bound exciton to the free hole and electron polarons in conjugated polymer chains is introduced and applied to polythiophenes.
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23
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Lerch A, Zimmermann JE, Namgalies A, Stallberg K, Höfer U. Two-photon photoemission spectroscopy of unoccupied electronic states at CuPc/PTCDA/Ag(1 1 1) interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:494001. [PMID: 30451155 DOI: 10.1088/1361-648x/aaec53] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The unoccupied electronic structure of stacked layers of copper(II)phthalocyanine (CuPc) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on Ag(1 1 1) has been investigated by means of two-photon photoemission (2PPE). We find a rich electronic structure comprising at least five unoccupied electronic states which we identify based on their energetic position and their dispersion in momentum space. More specifically, we observe the first and the second image-potential states of the modified Ag(1 1 1) surface, as well as the metal-organic interface state (IS) inherent to the PTCDA/Ag(1 1 1) interface. Moreover, two additional molecular features are observed for the CuPc/PTCDA/Ag(1 1 1) system which we attribute to an unoccupied molecular orbital (LUMO + 2) of CuPc. The 2PPE intensity of the IS exhibits a pronounced dependence on the pump photon energy, which closely follows the optical absorption of the outer molecular layer. This strongly points to charge transfer from the optically excited molecules to the interface state.
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Affiliation(s)
- A Lerch
- Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, 35032 Marburg, Germany
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24
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Yang W, Yao Y, Guo P, Sun H, Luo Y. Optimum driving energy for achieving balanced open-circuit voltage and short-circuit current density in organic bulk heterojunction solar cells. Phys Chem Chem Phys 2018; 20:29866-29875. [PMID: 30468215 DOI: 10.1039/c8cp05145c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Organic bulk heterojunction solar cells generally suffer from a trade-off between the open circuit voltage (Voc) and the short circuit current density (Jsc) under a given donor/acceptor (D/A) interfacial energetic offset (or the so-called driving force). Here we theoretically investigate the optimum driving energy required for achieving the balanced Jsc and Voc simultaneously. To this end, the Jscversus the driving force ΔE curves are calculated under two different charge separation mechanisms by employing the drift-diffusion method. For the Marcus incoherent mechanism, the curve features a high plateau in a broad range of ΔE starting from 0.2 eV, which is due to the accumulation of undissociated excitons within their lifetime and signifies the possibility of obtaining a sizable Jsc under a ΔE value much smaller than the reorganization energy. After incorporating both the electron and hole transfer pathways into the device model, the calculated J-V curves are comparable to experimentally measured ones foractual blended systems of different driving forces. For the coherent mechanism, it is demonstrated that the maximum Jsc can also be achieved under the ΔE of 0.2 eV if a large proportion of the high-lying delocalized states are harvested through tuning the density of states for the charge transfer excitons to reduce the sub-gap states. This theoretical work revealed quantitatively the relationship between the interfacial energy offsets and device performance, and also provides some guidelines for identifying the macroscopic features of the actual charge separation mechanisms in bulk heterojunction solar cells.
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Affiliation(s)
- Wenchao Yang
- Key Laboratory of Microelectronics and Energy of Henan, School of Physics and Electronic Engineering, Xinyang Normal University, Xinyang, 464000, China.
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25
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Aplan MP, Munro JM, Lee Y, Brigeman AN, Grieco C, Wang Q, Giebink NC, Dabo I, Asbury JB, Gomez ED. Revealing the Importance of Energetic and Entropic Contributions to the Driving Force for Charge Photogeneration. ACS APPLIED MATERIALS & INTERFACES 2018; 10:39933-39941. [PMID: 30360072 DOI: 10.1021/acsami.8b12077] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Despite significant recent progress, much about the mechanism for charge photogeneration in organic photovoltaics remains unknown. Here, we use conjugated block copolymers as model systems to examine the effects of energetic and entropic driving forces in organic donor-acceptor materials. The block copolymers are designed such that an electron donor block and an electron acceptor block are covalently linked, embedding a donor-acceptor interface within the molecular structure. This enables model studies in solution where processes occurring between one donor and one acceptor are examined. First, energy levels and dielectric constants that govern the driving force for charge transfer are systematically tuned and charge transfer within individual block copolymer chains is quantified. Results indicate that in isolated chains, a significant driving force of ∼0.3 eV is necessary to facilitate significant exciton dissociation to charge-transfer states. Next, block copolymers are cast into films, allowing for intermolecular interactions and charge delocalization over multiple chains. In the solid state, charge transfer is significantly enhanced relative to isolated block copolymer chains. Using Marcus Theory, we conclude that changes in the energetic driving force alone cannot explain the increased efficiency of exciton dissociation to charge-transfer states in the solid state. This implies that increasing the number of accessible states for charge transfer introduces an entropic driving force that can play an important role in the charge-generation mechanism of organic materials, particularly in systems where the excited state energy level is close to that of the charge-transfer state.
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26
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Kafle TR, Kattel B, Wang T, Chan WL. The relationship between the coherent size, binding energy and dissociation dynamics of charge transfer excitons at organic interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:454001. [PMID: 30265252 DOI: 10.1088/1361-648x/aae50b] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
At organic semiconductor interfaces, an electron and a hole can be bound Coulombically to form an interfacial charge transfer (CT) exciton. It is still under debate how a CT exciton can overcome its strong binding and dissociate into free carriers. Experimentally, capturing the evolution of the CT exciton on time (fs-ps) and length scales (nm) in which the dissociation process occurs is challenging. To overcome this challenge, time-resolved two photon photoemission spectroscopy is used to measure the binding energies and electronic coherent sizes of a series of CT states at organic interfaces, and capture the temporal dynamics of these CT excitons after their excitation. Using zinc phthalocyanine (ZnPc)/fullerene (C60) interface as a model system, it is shown that the interfacial CT process first populates a hot CT state with a coherent size of ~4 nm. Hot and delocalized CT excitons subsequently relax into CT excitons with lower energies and smaller coherent sizes. To correlate the CT exciton properties with the dissociation efficiency, we develop a method that exploits graphene field effect transistors to probe the rate and yield of free carrier generation at the interface. Our results show that exciton dissociation can be more efficient if one can extract electrons from the hot and delocalized CT state. We propose a cascade structure that would serve this purpose.
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Affiliation(s)
- Tika R Kafle
- Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045, United States of America
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27
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Wang Y, Ke Y, Zhao Y. The hierarchical and perturbative forms of stochastic Schrödinger equations and their applications to carrier dynamics in organic materials. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2018. [DOI: 10.1002/wcms.1375] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Yu‐Chen Wang
- State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
| | - Yaling Ke
- State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
| | - Yi Zhao
- State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Lab of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
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28
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Shi L, Lee CK, Willard AP. The Enhancement of Interfacial Exciton Dissociation by Energetic Disorder Is a Nonequilibrium Effect. ACS CENTRAL SCIENCE 2017; 3:1262-1270. [PMID: 29296666 PMCID: PMC5746863 DOI: 10.1021/acscentsci.7b00404] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Indexed: 05/29/2023]
Abstract
The dissociation of excited electron-hole pairs is a microscopic process that is fundamental to the performance of photovoltaic systems. For this process to be successful, the oppositely charged electron and hole must overcome an electrostatic binding energy before they undergo ground state recombination. It has been observed previously that the presence of energetic disorder can lead to a reduction in recombination losses. Here we investigate this effect using a simple model of charge dynamics at a donor-acceptor interface. We consider the effect of spatial variations in electronic energy levels, such as those that arise in disordered molecular systems, on dissociation yield and demonstrate that it is maximized with a finite amount of disorder. We demonstrate that this is a nonequilibrium effect that is mediated by the dissipation driven formation of partially dissociated intermediate states that are long-lived because they cannot easily recombine. We present a kinetic model that incorporates these states and show that it is capable of reproducing similar behavior when it is parametrized with nonequilibrium rates.
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Affiliation(s)
- Liang Shi
- Chemistry and Chemical Biology, University of California, Merced, California 95343, United States
| | - Chee Kong Lee
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Adam P Willard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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29
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Tamai Y, Fan Y, Kim VO, Ziabrev K, Rao A, Barlow S, Marder SR, Friend RH, Menke SM. Ultrafast Long-Range Charge Separation in Nonfullerene Organic Solar Cells. ACS NANO 2017; 11:12473-12481. [PMID: 29148715 DOI: 10.1021/acsnano.7b06575] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Rapid, long-range charge separation in polymer-fullerene organic solar cells (OSCs) enables electrons and holes to move beyond their Coulomb capture radius and overcome geminate recombination. Understanding the nature of charge generation and recombination mechanisms in efficient, nonfullerene-acceptor-based OSCs are critical to further improve device performance. Here we report charge dynamics in an OSC using a perylene diimide (PDI) dimer acceptor. We use transient absorption spectroscopy to track the time evolution of electroabsorption caused by the dipolar electric field generated between electron-hole pairs as they separate after ionization at the donor-acceptor interface. We show that charges separate rapidly (<1 ps) and that free charge carriers are generated very efficiently (∼90% quantum yield). However, in the PDI-based OSC, external charge extraction is impaired by faster nongeminate decay to the ground state and to lower-lying triplet states.
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Affiliation(s)
- Yasunari Tamai
- Cavendish Laboratory, Department of Physics, University of Cambridge , Cambridge CB3 0HE, United Kingdom
| | - Yeli Fan
- Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States
| | - Vincent O Kim
- Cavendish Laboratory, Department of Physics, University of Cambridge , Cambridge CB3 0HE, United Kingdom
| | - Kostiantyn Ziabrev
- Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States
| | - Akshay Rao
- Cavendish Laboratory, Department of Physics, University of Cambridge , Cambridge CB3 0HE, United Kingdom
| | - Stephen Barlow
- Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States
| | - Seth R Marder
- Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States
| | - Richard H Friend
- Cavendish Laboratory, Department of Physics, University of Cambridge , Cambridge CB3 0HE, United Kingdom
| | - S Matthew Menke
- Cavendish Laboratory, Department of Physics, University of Cambridge , Cambridge CB3 0HE, United Kingdom
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30
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Ke Y, Zhao Y. Perturbation expansions of stochastic wavefunctions for open quantum systems. J Chem Phys 2017; 147:184103. [DOI: 10.1063/1.4996737] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yaling Ke
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People’s Republic of China
| | - Yi Zhao
- State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People’s Republic of China
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31
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Ponseca CS, Chábera P, Uhlig J, Persson P, Sundström V. Ultrafast Electron Dynamics in Solar Energy Conversion. Chem Rev 2017; 117:10940-11024. [DOI: 10.1021/acs.chemrev.6b00807] [Citation(s) in RCA: 211] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Carlito S. Ponseca
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Pavel Chábera
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Jens Uhlig
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Petter Persson
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Villy Sundström
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
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32
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Impact of interfacial molecular orientation on radiative recombination and charge generation efficiency. Nat Commun 2017; 8:79. [PMID: 28724989 PMCID: PMC5517510 DOI: 10.1038/s41467-017-00107-4] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Accepted: 05/31/2017] [Indexed: 12/03/2022] Open
Abstract
A long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics—however, the results have important implications on the operation of all optoelectronic devices with donor/acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting in larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation. Molecular orientation profoundly affects the performance of donor-acceptor heterojunctions, whilst it has remained challenging to investigate the detail. Using a controllable interface, Ran et al. show that the edge-on geometries improve charge generation at the cost of non-radiative recombination loss.
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33
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Wang T, Kafle TR, Kattel B, Chan WL. A Multidimensional View of Charge Transfer Excitons at Organic Donor–Acceptor Interfaces. J Am Chem Soc 2017; 139:4098-4106. [DOI: 10.1021/jacs.6b13312] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ti Wang
- Department of Physics and
Astronomy, University of Kansas, Lawrence, Kansas 66045, United States
| | - Tika R. Kafle
- Department of Physics and
Astronomy, University of Kansas, Lawrence, Kansas 66045, United States
| | - Bhupal Kattel
- Department of Physics and
Astronomy, University of Kansas, Lawrence, Kansas 66045, United States
| | - Wai-Lun Chan
- Department of Physics and
Astronomy, University of Kansas, Lawrence, Kansas 66045, United States
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34
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Charge Carrier Generation, Recombination, and Extraction in Polymer–Fullerene Bulk Heterojunction Organic Solar Cells. ELEMENTARY PROCESSES IN ORGANIC PHOTOVOLTAICS 2017. [DOI: 10.1007/978-3-319-28338-8_11] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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35
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Dynamics of the triplet-pair state reveals the likely coexistence of coherent and incoherent singlet fission in crystalline hexacene. Nat Chem 2016; 9:341-346. [DOI: 10.1038/nchem.2665] [Citation(s) in RCA: 131] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Accepted: 10/03/2016] [Indexed: 12/19/2022]
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36
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Yao Y, Xie X, Ma H. Ultrafast Long-Range Charge Separation in Organic Photovoltaics: Promotion by Off-Diagonal Vibronic Couplings and Entropy Increase. J Phys Chem Lett 2016; 7:4830-4835. [PMID: 27934051 DOI: 10.1021/acs.jpclett.6b02400] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The exciton dissociation in a model donor/acceptor heterojunction with electron-phonon couplings is simulated by a full quantum dynamical method, in which ultrafast long-range charge separation is observed. Such a novel scenario does not undergo short-range interfacial (pinned) charge transfer states, but can be mainly ascribed to the quantum resonance between local Frenkel excited states and a broad array of long-range charge transfer (LRCT) states assisted by the moderate off-diagonal vibronic couplings. The entropy-increasing effect associated with the very dense density of states for LRCT states is also found to be beneficial for lowering the free energy barrier for charge generation in organic solar cells.
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Affiliation(s)
- Yao Yao
- Department of Physics, South China University of Technology , Guangzhou 510640, China
| | - Xiaoyu Xie
- Key Laboratory of Mesoscopic Chemistry of MOE, Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University , Nanjing 210023, China
| | - Haibo Ma
- Key Laboratory of Mesoscopic Chemistry of MOE, Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University , Nanjing 210023, China
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37
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Hood SN, Kassal I. Entropy and Disorder Enable Charge Separation in Organic Solar Cells. J Phys Chem Lett 2016; 7:4495-4500. [PMID: 27783509 DOI: 10.1021/acs.jpclett.6b02178] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Although organic heterojunctions can separate charges with near-unity efficiency and on a subpicosecond time scale, the full details of the charge-separation process remain unclear. In typical models, the Coulomb binding between the electron and the hole can exceed the thermal energy kBT by an order of magnitude, suggesting that it is impossible for the charges to separate before recombining. Here, we consider the entropic contribution to charge separation in the presence of disorder and find that even modest amounts of disorder have a decisive effect, reducing the charge-separation barrier to about kBT or eliminating it altogether. Therefore, the charges are usually not thermodynamically bound at all and could separate spontaneously if the kinetics otherwise allowed it. Our conclusion holds despite the worst-case assumption of localized, thermalized carriers and is only strengthened if mechanisms like delocalization or "hot" states are also present.
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Affiliation(s)
- Samantha N Hood
- Centre for Engineered Quantum Systems, Centre for Organic Photonics and Electronics and School of Mathematics and Physics, The University of Queensland , Brisbane, Queensland 4072, Australia
| | - Ivan Kassal
- Centre for Engineered Quantum Systems, Centre for Organic Photonics and Electronics and School of Mathematics and Physics, The University of Queensland , Brisbane, Queensland 4072, Australia
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38
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Abstract
Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjugated polymers are considered, and their applications in organic solar cells, photodetectors, and photorefractive devices are discussed.
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Affiliation(s)
- Oksana Ostroverkhova
- Department of Physics, Oregon State University , Corvallis, Oregon 97331, United States
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39
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Jakowetz AC, Böhm ML, Zhang J, Sadhanala A, Huettner S, Bakulin AA, Rao A, Friend RH. What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends. J Am Chem Soc 2016; 138:11672-9. [DOI: 10.1021/jacs.6b05131] [Citation(s) in RCA: 160] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Andreas C. Jakowetz
- Cavendish
Laboratory, Department of Physics, University of Cambridge, J J Thomson
Avenue, Cambridge CB3 0HE, United Kingdom
| | - Marcus L. Böhm
- Cavendish
Laboratory, Department of Physics, University of Cambridge, J J Thomson
Avenue, Cambridge CB3 0HE, United Kingdom
| | - Jiangbin Zhang
- Cavendish
Laboratory, Department of Physics, University of Cambridge, J J Thomson
Avenue, Cambridge CB3 0HE, United Kingdom
| | - Aditya Sadhanala
- Cavendish
Laboratory, Department of Physics, University of Cambridge, J J Thomson
Avenue, Cambridge CB3 0HE, United Kingdom
| | - Sven Huettner
- Fakultät
für Biologie, Chemie und Geowissenschaften, University Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany
| | - Artem A. Bakulin
- Cavendish
Laboratory, Department of Physics, University of Cambridge, J J Thomson
Avenue, Cambridge CB3 0HE, United Kingdom
- Department
of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom
| | - Akshay Rao
- Cavendish
Laboratory, Department of Physics, University of Cambridge, J J Thomson
Avenue, Cambridge CB3 0HE, United Kingdom
| | - Richard H. Friend
- Cavendish
Laboratory, Department of Physics, University of Cambridge, J J Thomson
Avenue, Cambridge CB3 0HE, United Kingdom
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40
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Zhang CZ, Gu SD, Shen D, Yuan Y, Zhang M. Synthesis of an A-D-A type of molecule used as electron acceptor for improving charge transfer in organic solar cells. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2016.06.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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41
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Stolterfoht M, Armin A, Shoaee S, Kassal I, Burn P, Meredith P. Slower carriers limit charge generation in organic semiconductor light-harvesting systems. Nat Commun 2016; 7:11944. [PMID: 27324720 PMCID: PMC4919513 DOI: 10.1038/ncomms11944] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 05/16/2016] [Indexed: 01/28/2023] Open
Abstract
Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron-hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers.
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Affiliation(s)
- Martin Stolterfoht
- Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Ardalan Armin
- Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Safa Shoaee
- Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Ivan Kassal
- Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.,Centre for Engineered Quantum Systems, Centre for Quantum Computation and Communication Technology, School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Paul Burn
- Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Paul Meredith
- Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia
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42
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Maggio E, Martsinovich N, Troisi A. Continuum and atomistic description of excess electrons in TiO2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:074004. [PMID: 26808551 DOI: 10.1088/0953-8984/28/7/074004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The modelling of an excess electron in a semiconductor in a prototypical dye sensitised solar cell is carried out using two complementary approaches: atomistic simulation of the TiO2 nanoparticle surface is complemented by a dielectric continuum model of the solvent-semiconductor interface. The two methods are employed to characterise the bound (excitonic) states formed by the interaction of the electron in the semiconductor with a positive charge opposite the interface. Density-functional theory (DFT) calculations show that the excess electron in TiO2 in the presence of a counterion is not fully localised but extends laterally over a large region, larger than system sizes accessible to DFT calculations. The numerical description of the excess electron at the semiconductor-electrolyte interface based on the continuum model shows that the exciton is also delocalised over a large area: the exciton radius can have values from tens to hundreds of Ångströms, depending on the nature of the semiconductor (characterised by the dielectric constant and the electron effective mass in our model).
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Affiliation(s)
- Emanuele Maggio
- Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, UK
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43
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D'Avino G, Muccioli L, Olivier Y, Beljonne D. Charge Separation and Recombination at Polymer-Fullerene Heterojunctions: Delocalization and Hybridization Effects. J Phys Chem Lett 2016; 7:536-40. [PMID: 26785294 DOI: 10.1021/acs.jpclett.5b02680] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We address charge separation and recombination in polymer/fullerene solar cells with a multiscale modeling built from accurate atomistic inputs and accounting for disorder, interface electrostatics and genuine quantum effects on equal footings. Our results show that bound localized charge transfer states at the interface coexist with a large majority of thermally accessible delocalized space-separated states that can be also reached by direct photoexcitation, thanks to their strong hybridization with singlet polymer excitons. These findings reconcile the recent experimental reports of ultrafast exciton separation ("hot" process) with the evidence that high quantum yields do not require excess electronic or vibrational energy ("cold" process), and show that delocalization, by shifting the density of charge transfer states toward larger effective electron-hole radii, may reduce energy losses through charge recombination.
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Affiliation(s)
- Gabriele D'Avino
- Laboratory for Chemistry of Novel Materials, University of Mons , 7000 Mons, Belgium
| | - Luca Muccioli
- Laboratoire de Chimie des Polymères Organiques, UMR 5629, University of Bordeaux , 33607 Pessac, France
| | - Yoann Olivier
- Laboratory for Chemistry of Novel Materials, University of Mons , 7000 Mons, Belgium
| | - David Beljonne
- Laboratory for Chemistry of Novel Materials, University of Mons , 7000 Mons, Belgium
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44
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Bittner ER, Kelley A. The role of structural fluctuations and environmental noise in the electron/hole separation kinetics at organic polymer bulk-heterojunction interfaces. Phys Chem Chem Phys 2016; 17:28853-9. [PMID: 26449151 DOI: 10.1039/c5cp05037e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
We investigate the electronic dynamics of a model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and a [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide an estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We find that the lowest few excited states of a model interface are rapidly mixed by C[double bond, length as m-dash]C bond fluctuations such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on a time scale of 20 fs. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.
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Affiliation(s)
- Eric R Bittner
- Department of Chemistry and Centre for Quantum Engineering, University of Houston, Houston, TX 77204, USA.
| | - Allen Kelley
- Department of Chemistry and Centre for Quantum Engineering, University of Houston, Houston, TX 77204, USA.
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45
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Cunningham PD, Lane PA, Melinger JS, Esenturk O, Heilweil EJ. Probing Charge Transfer and Hot Carrier Dynamics in Organic Solar Cells with Terahertz Spectroscopy. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2016. [PMID: 28649166 DOI: 10.1117/12.2228379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Time-resolved terahertz spectroscopy (TRTS) was used to explore charge generation, transfer, and the role of hot carriers in organic solar cell materials. Two model molecular photovoltaic systems were investigated: with zinc phthalocyanine (ZnPc) or alpha-sexathiophene (α-6T) as the electron donors and buckminsterfullerene (C60) as the electron acceptor. TRTS provides charge carrier conductivity dynamics comprised of changes in both population and mobility. By using time-resolved optical spectroscopy in conjunction with TRTS, these two contributions can be disentangled. The sub-picosecond photo-induced conductivity decay dynamics of C60 were revealed to be caused by auto-ionization: the intrinsic process by which charge is generated in molecular solids. In donor-acceptor blends, the long-lived photo-induced conductivity is used for weight fraction optimization of the constituents. In nanoscale multilayer films, the photo-induced conductivity identifies optimal layer thicknesses. In films of ZnPc/C60, electron transfer from ZnPc yields hot charges that localize and become less mobile as they thermalize. Excitation of high-lying Franck Condon states in C60 followed by hole-transfer to ZnPc similarly produces hot charge carriers that self-localize; charge transfer clearly precedes carrier cooling. This picture is contrasted to charge transfer in α-6T/C60, where hole transfer takes place from a thermalized state and produces equilibrium carriers that do not show characteristic signs of cooling and self-localization. These results illustrate the value of terahertz spectroscopic methods for probing charge transfer reactions.
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Affiliation(s)
| | - Paul A Lane
- U.S. Naval Research Laboratory, Washington, DC 20375, United States
| | | | - Okan Esenturk
- Chemistry Department, Middle East Technical University, Ankara, Turkey
| | - Edwin J Heilweil
- National Institute of Standards and Technology, Gaithersburg, MD 20899, United States
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