1
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Zheng Y, Venkatesh R, Rojas-Gatjens E, Reichmanis E, Silva-Acuña C. Exciton Bimolecular Annihilation Dynamics in Push-Pull Semiconductor Polymers. J Phys Chem Lett 2024; 15:272-280. [PMID: 38166236 PMCID: PMC10788955 DOI: 10.1021/acs.jpclett.3c03094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Revised: 12/17/2023] [Accepted: 12/28/2023] [Indexed: 01/04/2024]
Abstract
Exciton-exciton annihilation is a ubiquitous nonlinear dynamic phenomenon in materials hosting Frenkel excitons. In this work, we investigate the nonlinear exciton dynamics of an electron push-pull conjugated polymer by fluence-dependent transient absorption and excitation-correlation photoluminescence spectroscopy, where we can quantitatively show the latter to be a more selective probe of the nonlinear dynamics. Simulations based on a time-independent exciton annihilation model show a decreasing trend for the extracted annihilation rates with excitation fluence. Further investigation of the fluence-dependent transients suggests that the exciton-exciton annihilation bimolecular rates are not constant in time, displaying a t-1/2 time dependence, which we rationalize as reflective of one-dimensional exciton diffusion, with a diffusion length estimated to be 9 ± 2 nm. In addition, exciton annihilation gives rise to a long-lived species that recombines on a nanosecond time scale. Our conclusions shed broad light onto nonlinear exciton dynamics in push-pull conjugated polymers.
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Affiliation(s)
- Yulong Zheng
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, United States
| | - Rahul Venkatesh
- School
of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332, United States
| | - Esteban Rojas-Gatjens
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, United States
| | - Elsa Reichmanis
- Department
of Chemical & Biomolecular Engineering, Lehigh University, 124 E. Morton Street, Bethlehem, Pennsylvania 18015, United States
| | - Carlos Silva-Acuña
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, United States
- Institut
Courtois & Département de physique, Université de Montréal, 1375 Avenue Thérèse-Lavoie-Roux, Montréal H2V 0B3, Québec, Canada
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2
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Dash A, Guchait S, Scheunemann D, Vijayakumar V, Leclerc N, Brinkmann M, Kemerink M. Spontaneous Modulation Doping in Semi-Crystalline Conjugated Polymers Leads to High Conductivity at Low Doping Concentration. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023:e2311303. [PMID: 38118058 DOI: 10.1002/adma.202311303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 12/05/2023] [Indexed: 12/22/2023]
Abstract
The possibility to control the charge carrier density through doping is one of the defining properties of semiconductors. For organic semiconductors, the doping process is known to come with several problems associated with the dopant compromising the charge carrier mobility by deteriorating the host morphology and/or introducing Coulomb traps. While for inorganic semiconductors these factors can be mitigated through (top-down) modulation doping, this concept has not been employed in organics. Here, this work shows that properly chosen host/dopant combinations can give rise to spontaneous, bottom-up modulation doping, in which the dopants preferentially sit in an amorphous phase, while the actual charge transport occurs predominantly in a crystalline phase with an unaltered microstructure, spatially separating dopants and mobile charges. Combining experiments and numerical simulations, this work shows that this leads to exceptionally high conductivities at relatively low dopant concentrations.
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Affiliation(s)
- Aditya Dash
- Institute for Molecular Systems Engineering and Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120, Heidelberg, Germany
| | - Shubhradip Guchait
- Institute Charles Sadron, UPR022, CNRS - Université de Strasbourg, Strasbourg, 67034, France
| | - Dorothea Scheunemann
- Institute for Molecular Systems Engineering and Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120, Heidelberg, Germany
| | - Vishnu Vijayakumar
- Institute Charles Sadron, UPR022, CNRS - Université de Strasbourg, Strasbourg, 67034, France
- Department of Chemistry-Ångström, Physical Chemistry, Uppsala University, Uppsala, 75120, Sweden
| | - Nicolas Leclerc
- Université de Strasbourg, CNRS, ICPEES UMR 7515, Strasbourg, F-67087, France
| | - Martin Brinkmann
- Institute Charles Sadron, UPR022, CNRS - Université de Strasbourg, Strasbourg, 67034, France
| | - Martijn Kemerink
- Institute for Molecular Systems Engineering and Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120, Heidelberg, Germany
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3
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Zheng Y, Venkatesh R, Callaway CP, Viersen C, Fagbohungbe KH, Liu AL, Risko C, Reichmanis E, Silva-Acuña C. Chain Conformation and Exciton Delocalization in a Push-Pull Conjugated Polymer. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2023; 35:10258-10267. [PMID: 38107193 PMCID: PMC10720347 DOI: 10.1021/acs.chemmater.3c02665] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Accepted: 10/24/2023] [Indexed: 12/19/2023]
Abstract
Linear and nonlinear optical line shapes reveal details of excitonic structure in polymer semiconductors. We implement absorption, photoluminescence, and transient absorption spectroscopies in DPP-DTT, an electron push-pull copolymer, to explore the relationship between their spectral line shapes and chain conformation, deduced from resonance Raman spectroscopy and from ab initio calculations. The viscosity of precursor polymer solutions before film casting displays a transition that suggests gel formation above a critical concentration. Upon crossing this viscosity deflection concentration, the line shape analysis of the absorption spectra within a photophysical aggregate model reveals a gradual increase in interchain excitonic coupling. We also observe a red-shifted and line-narrowed steady-state photoluminescence spectrum along with increasing resonance Raman intensity in the stretching and torsional modes of the dithienothiophene unit, which suggests a longer exciton coherence length along the polymer-chain backbone. Furthermore, we observe a change of line shape in the photoinduced absorption component of the transient absorption spectrum. The derivative-like line shape may originate from two possibilities: a new excited-state absorption or Stark effect, both of which are consistent with the emergence of a high-energy shoulder as seen in both photoluminescence and absorption spectra. Therefore, we conclude that the exciton is more dispersed along the polymer chain backbone with increasing concentrations, leading to the hypothesis that polymer chain order is enhanced when the push-pull polymers are processed at higher concentrations. Thus, tuning the microscopic chain conformation by concentration would be another factor of interest when considering the polymer assembly pathways for pursuing large-area and high-performance organic optoelectronic devices.
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Affiliation(s)
- Yulong Zheng
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, United States
| | - Rahul Venkatesh
- School
of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332, United States
| | - Connor P. Callaway
- Department
of Chemistry and Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Campbell Viersen
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, United States
| | - Kehinde H. Fagbohungbe
- Department
of Chemistry and Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Aaron L. Liu
- School
of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332, United States
| | - Chad Risko
- Department
of Chemistry and Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506, United States
| | - Elsa Reichmanis
- Department
of Chemical & Biomolecular Engineering, Lehigh University, 124 East Morton Street, Bethlehem, Pennsylvania 18015, United States
| | - Carlos Silva-Acuña
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, United States
- School
of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, Georgia 30332, United States
- School
of Materials Science and Engineering, Georgia
Institute of Technology, North Avenue, Atlanta, Georgia 30332, United States
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4
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Rojas-Gatjens E, Yallum KM, Shi Y, Zheng Y, Bills T, Perini CAR, Correa-Baena JP, Ginger DS, Banerji N, Silva-Acuña C. Resolving Nonlinear Recombination Dynamics in Semiconductors via Ultrafast Excitation Correlation Spectroscopy: Photoluminescence versus Photocurrent Detection. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2023; 127:15969-15977. [PMID: 37609378 PMCID: PMC10440815 DOI: 10.1021/acs.jpcc.3c04755] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Indexed: 08/24/2023]
Abstract
We explore the application of excitation correlation spectroscopy to detect nonlinear photophysical dynamics in two distinct semiconductor classes through time-integrated photoluminescence and photocurrent measurements. In this experiment, two variably delayed femtosecond pulses excite the semiconductor, and the time-integrated photoluminescence or photocurrent component arising from the nonlinear dynamics of the populations induced by each pulse is measured as a function of inter-pulse delay by phase-sensitive detection with a lock-in amplifier. We focus on two limiting materials systems with contrasting optical properties: a prototypical lead-halide perovskite (LHP) solar cell, in which primary photoexcitations are charge photocarriers, and a single-component organic-semiconductor diode, which features Frenkel excitons as primary photoexcitations. The photoexcitation dynamics perceived by the two detection schemes in these contrasting systems are distinct. Nonlinear-dynamic contributions in the photoluminescence detection scheme arise from contributions to radiative recombination in both materials systems, while photocurrent arises directly in the LHP but indirectly following exciton dissociation in the organic system. Consequently, the basic photophysics of the two systems are reflected differently when comparing measurements with the two detection schemes. Our results indicate that photoluminescence detection in the LHP system provides valuable information about trap-assisted and Auger recombination processes, but that these processes are convoluted in a nontrivial way in the photocurrent response and are therefore difficult to differentiate. In contrast, the organic-semiconductor system exhibits more directly correlated responses in the nonlinear photoluminescence and photocurrent measurements, as charge carriers are secondary excitations only generated through exciton dissociation processes. We propose that bimolecular annihilation pathways mainly contribute to the generation of charge carriers in single-component organic semiconductor devices. Overall, our work highlights the utility of excitation correlation spectroscopy in modern semiconductor materials research, particularly in the analysis of nonlinear photophysical processes, which are deterministic for their electronic and optical properties.
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Affiliation(s)
- Esteban Rojas-Gatjens
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30332, United States
| | - Kaila M. Yallum
- Department
of Chemistry, Biochemistry, and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, Bern CH-3012, Switzerland
| | - Yangwei Shi
- Department
of Chemistry, University of Washington, Seattle, Washington 98195, United States
- Molecular
Engineering & Sciences Institute, University
of Washington, Seattle, Washington 98195, United States
| | - Yulong Zheng
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30332, United States
| | - Tyler Bills
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30332, United States
| | - Carlo A. R. Perini
- School
of Materials Science and Engineering, Georgia
Institute of Technology, Atlanta, Georgia 30332, United States
| | - Juan-Pablo Correa-Baena
- School
of Materials Science and Engineering, Georgia
Institute of Technology, Atlanta, Georgia 30332, United States
| | - David S. Ginger
- Department
of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Natalie Banerji
- Department
of Chemistry, Biochemistry, and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, Bern CH-3012, Switzerland
| | - Carlos Silva-Acuña
- School
of Chemistry and Biochemistry, Georgia Institute
of Technology, Atlanta, Georgia 30332, United States
- School
of Materials Science and Engineering, Georgia
Institute of Technology, Atlanta, Georgia 30332, United States
- School of
Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
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5
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Novel ionizing radiation induced reactions of poly(3-hexylthiophene). Polym Degrad Stab 2022. [DOI: 10.1016/j.polymdegradstab.2022.110129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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6
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Direct observation of ultrafast exciton localization in an organic semiconductor with soft X-ray transient absorption spectroscopy. Nat Commun 2022; 13:3414. [PMID: 35701418 PMCID: PMC9198071 DOI: 10.1038/s41467-022-31008-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 05/24/2022] [Indexed: 12/02/2022] Open
Abstract
The localization dynamics of excitons in organic semiconductors influence the efficiency of charge transfer and separation in these materials. Here we apply time-resolved X-ray absorption spectroscopy to track photoinduced dynamics of a paradigmatic crystalline conjugated polymer: poly(3-hexylthiophene) (P3HT) commonly used in solar cell devices. The π→π* transition, the first step of solar energy conversion, is pumped with a 15 fs optical pulse and the dynamics are probed by an attosecond soft X-ray pulse at the carbon K-edge. We observe X-ray spectroscopic signatures of the initially hot excitonic state, indicating that it is delocalized over multiple polymer chains. This undergoes a rapid evolution on a sub 50 fs timescale which can be directly associated with cooling and localization to form either a localized exciton or polaron pair. A detailed understanding of ultrafast exciton dynamics is crucial for improving the efficiency of organic light-harvesting-devices. Here, the authors track exciton localization on a sub-50 fs timescale in an organic semiconductor using time resolved soft x-ray absorption spectroscopy.
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7
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Price MB, Hume PA, Ilina A, Wagner I, Tamming RR, Thorn KE, Jiao W, Goldingay A, Conaghan PJ, Lakhwani G, Davis NJLK, Wang Y, Xue P, Lu H, Chen K, Zhan X, Hodgkiss JM. Free charge photogeneration in a single component high photovoltaic efficiency organic semiconductor. Nat Commun 2022; 13:2827. [PMID: 35595764 PMCID: PMC9122989 DOI: 10.1038/s41467-022-30127-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 04/15/2022] [Indexed: 11/09/2022] Open
Abstract
Organic photovoltaics (OPVs) promise cheap and flexible solar energy. Whereas light generates free charges in silicon photovoltaics, excitons are normally formed in organic semiconductors due to their low dielectric constants, and require molecular heterojunctions to split into charges. Recent record efficiency OPVs utilise the small molecule, Y6, and its analogues, which – unlike previous organic semiconductors – have low band-gaps and high dielectric constants. We show that, in Y6 films, these factors lead to intrinsic free charge generation without a heterojunction. Intensity-dependent spectroscopy reveals that 60–90% of excitons form free charges at AM1.5 light intensity. Bimolecular recombination, and hole traps constrain single component Y6 photovoltaics to low efficiencies, but recombination is reduced by small quantities of donor. Quantum-chemical calculations reveal strong coupling between exciton and CT states, and an intermolecular polarisation pattern that drives exciton dissociation. Our results challenge how current OPVs operate, and renew the possibility of efficient single-component OPVs. When light hits organic semiconductors, bound charge pairs, called excitons, are usually produced. Here, the authors show that in the best performing organic solar material to date, free charges, rather than excitons, are directly created by light.
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Affiliation(s)
- Michael B Price
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand. .,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand.
| | - Paul A Hume
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand. .,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand.
| | - Aleksandra Ilina
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand.,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand
| | - Isabella Wagner
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand.,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand
| | - Ronnie R Tamming
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand.,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand.,Wellington UniVentures, Victoria University of Wellington, Wellington, New Zealand.,Robinson Research Institute, Faculty of Engineering, Victoria University of Wellington, Wellington, New Zealand.,The Dodd-Walls Centre for Photonic and Quantum Technologies, Dunedin, New Zealand
| | - Karen E Thorn
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand.,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand
| | - Wanting Jiao
- Ferrier Research Institute, Victoria University of Wellington, Wellington, New Zealand
| | - Alison Goldingay
- ARC Centre of Excellence in Exciton Science, School of Chemistry, University of Sydney, Sydney, NSW, Australia
| | - Patrick J Conaghan
- ARC Centre of Excellence in Exciton Science, School of Chemistry, University of Sydney, Sydney, NSW, Australia
| | - Girish Lakhwani
- ARC Centre of Excellence in Exciton Science, School of Chemistry, University of Sydney, Sydney, NSW, Australia
| | - Nathaniel J L K Davis
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand.,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand
| | - Yifan Wang
- School of Materials Science and Engineering, Peking University, Beijing, China.,College of Materials Science and Engineering, Qingdao University, Qingdao, China
| | - Peiyao Xue
- School of Materials Science and Engineering, Peking University, Beijing, China
| | - Heng Lu
- School of Materials Science and Engineering, Peking University, Beijing, China
| | - Kai Chen
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand.,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand.,Wellington UniVentures, Victoria University of Wellington, Wellington, New Zealand.,Robinson Research Institute, Faculty of Engineering, Victoria University of Wellington, Wellington, New Zealand.,The Dodd-Walls Centre for Photonic and Quantum Technologies, Dunedin, New Zealand
| | - Xiaowei Zhan
- School of Materials Science and Engineering, Peking University, Beijing, China
| | - Justin M Hodgkiss
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand. .,MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington, New Zealand.
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8
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Yu G, Li W, Gao H, Zhang M, Guo Y, Chen S. Boosting Reactive Oxygen Species Generation by Regulating Excitonic Effects in Porphyrinic Covalent Organic Frameworks. J Phys Chem Lett 2022; 13:2814-2823. [PMID: 35319207 DOI: 10.1021/acs.jpclett.2c00389] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Excitonic effects play a crucial role in determining the photocatalytic performance of polymer semiconductors, which has long been ignored. Herein, metal organic frameworks (MOFs, specially NH2-MIL-125) modifying porphyrinic covalent organic frameworks (COFs, specially DhaTph) have been proven to be a suitable model to regulate excitonic effects. The photoluminescence measurements prove that DhaTph presents strong excitonic effects, which can generate 1O2 through an energy transfer process. Remarkably, the construction of the NH2-MIL-125@DhaTph heterostructure can effectively facilitate the dissociation of excitons, resulting in distinct activation of O2 to O2•- and •OH. Benefiting from the enhanced generation of reactive oxygen species, the NH2-MIL-125@DhaTph composite exhibits a superior bactericidal effect and photocatalytic degradation performance. This work provides a deeper insight into the excitonic effects based on COFs during the photocatalytic process and opens a feasible avenue for the regulation of the excitonic effects in porphyrinic COFs.
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Affiliation(s)
- Guang Yu
- School of Materials Science & Engineering, Ocean University of China, Qingdao 266100, PR China
| | - Wen Li
- School of Materials Science & Engineering, Ocean University of China, Qingdao 266100, PR China
| | - Hui Gao
- School of Materials Science & Engineering, Ocean University of China, Qingdao 266100, PR China
| | - Mutian Zhang
- School of Materials Science & Engineering, Ocean University of China, Qingdao 266100, PR China
| | - Yiming Guo
- School of Materials Science & Engineering, Ocean University of China, Qingdao 266100, PR China
| | - Shougang Chen
- School of Materials Science & Engineering, Ocean University of China, Qingdao 266100, PR China
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9
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Dimitriev OP. Dynamics of Excitons in Conjugated Molecules and Organic Semiconductor Systems. Chem Rev 2022; 122:8487-8593. [PMID: 35298145 DOI: 10.1021/acs.chemrev.1c00648] [Citation(s) in RCA: 35] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The exciton, an excited electron-hole pair bound by Coulomb attraction, plays a key role in photophysics of organic molecules and drives practically important phenomena such as photoinduced mechanical motions of a molecule, photochemical conversions, energy transfer, generation of free charge carriers, etc. Its behavior in extended π-conjugated molecules and disordered organic films is very different and very rich compared with exciton behavior in inorganic semiconductor crystals. Due to the high degree of variability of organic systems themselves, the exciton not only exerts changes on molecules that carry it but undergoes its own changes during all phases of its lifetime, that is, birth, conversion and transport, and decay. The goal of this review is to give a systematic and comprehensive view on exciton behavior in π-conjugated molecules and molecular assemblies at all phases of exciton evolution with emphasis on rates typical for this dynamic picture and various consequences of the above dynamics. To uncover the rich variety of exciton behavior, details of exciton formation, exciton transport, exciton energy conversion, direct and reverse intersystem crossing, and radiative and nonradiative decay are considered in different systems, where these processes lead to or are influenced by static and dynamic disorder, charge distribution symmetry breaking, photoinduced reactions, electron and proton transfer, structural rearrangements, exciton coupling with vibrations and intermediate particles, and exciton dissociation and annihilation as well.
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Affiliation(s)
- Oleg P Dimitriev
- V. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine, pr. Nauki 41, Kyiv 03028, Ukraine
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10
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Sneyd AJ, Fukui T, Paleček D, Prodhan S, Wagner I, Zhang Y, Sung J, Collins SM, Slater TJA, Andaji-Garmaroudi Z, MacFarlane LR, Garcia-Hernandez JD, Wang L, Whittell GR, Hodgkiss JM, Chen K, Beljonne D, Manners I, Friend RH, Rao A. Efficient energy transport in an organic semiconductor mediated by transient exciton delocalization. SCIENCE ADVANCES 2021; 7:7/32/eabh4232. [PMID: 34348902 PMCID: PMC8336960 DOI: 10.1126/sciadv.abh4232] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 06/14/2021] [Indexed: 05/12/2023]
Abstract
Efficient energy transport is desirable in organic semiconductor (OSC) devices. However, photogenerated excitons in OSC films mostly occupy highly localized states, limiting exciton diffusion coefficients to below ~10-2 cm2/s and diffusion lengths below ~50 nm. We use ultrafast optical microscopy and nonadiabatic molecular dynamics simulations to study well-ordered poly(3-hexylthiophene) nanofiber films prepared using living crystallization-driven self-assembly, and reveal a highly efficient energy transport regime: transient exciton delocalization, where energy exchange with vibrational modes allows excitons to temporarily re-access spatially extended states under equilibrium conditions. We show that this enables exciton diffusion constants up to 1.1 ± 0.1 cm2/s and diffusion lengths of 300 ± 50 nm. Our results reveal the dynamic interplay between localized and delocalized exciton configurations at equilibrium conditions, calling for a re-evaluation of exciton dynamics and suggesting design rules to engineer efficient energy transport in OSC device architectures not based on restrictive bulk heterojunctions.
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Affiliation(s)
- Alexander J Sneyd
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
| | - Tomoya Fukui
- Department of Chemistry, University of Victoria, Victoria, BC V8P 5C2, Canada
- School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - David Paleček
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
| | - Suryoday Prodhan
- Laboratory for Chemistry of Novel Materials, University of Mons, Mons 7000, Belgium
| | - Isabella Wagner
- MacDiarmid Institute for Advanced Materials and Nanotechnology and School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6010, New Zealand
| | - Yifan Zhang
- Department of Chemistry, University of Victoria, Victoria, BC V8P 5C2, Canada
- School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - Jooyoung Sung
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
| | - Sean M Collins
- School of Chemical and Process Engineering and School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
| | - Thomas J A Slater
- Electron Physical Science Imaging Centre, Diamond Light Source Ltd., Oxfordshire OX11 0DE, UK
| | | | - Liam R MacFarlane
- Department of Chemistry, University of Victoria, Victoria, BC V8P 5C2, Canada
- School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - J Diego Garcia-Hernandez
- Department of Chemistry, University of Victoria, Victoria, BC V8P 5C2, Canada
- School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - Linjun Wang
- Center for Chemistry of Novel & High-Performance Materials, and Department of Chemistry, Zhejiang University, Hangzhou 310027, China
| | | | - Justin M Hodgkiss
- MacDiarmid Institute for Advanced Materials and Nanotechnology and School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6010, New Zealand
| | - Kai Chen
- MacDiarmid Institute for Advanced Materials and Nanotechnology and School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6010, New Zealand
- Robinson Research Institute, Faculty of Engineering, Victoria University of Wellington, Wellington 6012, New Zealand
- The Dodd-Walls Centre for Photonic and Quantum Technologies, Dunedin 9016, New Zealand
| | - David Beljonne
- Laboratory for Chemistry of Novel Materials, University of Mons, Mons 7000, Belgium.
| | - Ian Manners
- Department of Chemistry, University of Victoria, Victoria, BC V8P 5C2, Canada.
- School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - Richard H Friend
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
| | - Akshay Rao
- Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
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11
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Griggs S, Marks A, Bristow H, McCulloch I. n-Type organic semiconducting polymers: stability limitations, design considerations and applications. JOURNAL OF MATERIALS CHEMISTRY. C 2021; 9:8099-8128. [PMID: 34277009 PMCID: PMC8264852 DOI: 10.1039/d1tc02048j] [Citation(s) in RCA: 61] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 06/10/2021] [Indexed: 04/14/2023]
Abstract
This review outlines the design strategies which aim to develop high performing n-type materials in the fields of organic thin film transistors (OTFT), organic electrochemical transistors (OECT) and organic thermoelectrics (OTE). Figures of merit for each application and the limitations in obtaining these are set out, and the challenges with achieving consistent and comparable measurements are addressed. We present a thorough discussion of the limitations of n-type materials, particularly their ambient operational instability, and suggest synthetic methods to overcome these. This instability originates from the oxidation of the negative polaron of the organic semiconductor (OSC) by water and oxygen, the potentials of which commonly fall within the electrochemical window of n-type OSCs, and consequently require a LUMO level deeper than ∼-4 eV for a material with ambient stability. Recent high performing n-type materials are detailed for each application and their design principles are discussed to explain how synthetic modifications can enhance performance. This can be achieved through a number of strategies, including utilising an electron deficient acceptor-acceptor backbone repeat unit motif, introducing electron-withdrawing groups or heteroatoms, rigidification and planarisation of the polymer backbone and through increasing the conjugation length. By studying the fundamental synthetic design principles which have been employed to date, this review highlights a path to the development of promising polymers for n-type OSC applications in the future.
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Affiliation(s)
- Sophie Griggs
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford Oxford OX1 3TA UK
| | - Adam Marks
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford Oxford OX1 3TA UK
| | - Helen Bristow
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford Oxford OX1 3TA UK
| | - Iain McCulloch
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford Oxford OX1 3TA UK
- King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC) Thuwal 23955-6900 Saudi Arabia
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12
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Marina S, Kaufmann NP, Karki A, Gutiérrez-Meza E, Gutiérrez-Fernández E, Vollbrecht J, Solano E, Walker B, Bannock JH, de Mello J, Silva C, Nguyen TQ, Cangialosi D, Stingelin N, Martín J. The Importance of Quantifying the Composition of the Amorphous Intermixed Phase in Organic Solar Cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2005241. [PMID: 33089554 DOI: 10.1002/adma.202005241] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2020] [Revised: 09/15/2020] [Indexed: 06/11/2023]
Abstract
The relation of phase morphology and solid-state microstructure with organic photovoltaic (OPV) device performance has intensely been investigated over the last twenty years. While it has been established that a combination of donor:acceptor intermixing and presence of relatively phase-pure donor and acceptor domains is needed to get an optimum compromise between charge generation and charge transport/charge extraction, a quantitative picture of how much intermixing is needed is still lacking. This is mainly due to the difficulty in quantitatively analyzing the intermixed phase, which generally is amorphous. Here, fast scanning calorimetry, which allows measurement of device-relevant thin films (<200 nm thickness), is exploited to deduce the precise composition of the intermixed phase in bulk-heterojunction structures. The power of fast scanning calorimetry is illustrated by considering two polymer:fullerene model systems. Somewhat surprisingly, it is found that a relatively small fraction (<15 wt%) of an acceptor in the intermixed amorphous phase leads to efficient charge generation. In contrast, charge transport can only be sustained in blends with a significant amount of the acceptor in the intermixed phase (in this case: ≈58 wt%). This example shows that fast scanning calorimetry is an important tool for establishing a complete compositional characterization of organic bulk heterojunctions. Hence, it will be critical in advancing quantitative morphology-function models that allow for the rational design of these devices, and in delivering insights in, for example, solar cell degradation mechanisms via phase separation, especially for more complex high-performing systems such as nonfullerene acceptor:polymer bulk heterojunctions.
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Affiliation(s)
- Sara Marina
- POLYMAT, University of the Basque Country UPV/EHU, Av. de Tolosa 72, San Sebastián, 20018, Spain
| | | | - Akchheta Karki
- Center for Polymers and Organic Solids, University of California, Santa Barbara, CA, 93106, USA
| | - Elizabeth Gutiérrez-Meza
- School of Physics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | | | - Joachim Vollbrecht
- Center for Polymers and Organic Solids, University of California, Santa Barbara, CA, 93106, USA
| | - Eduardo Solano
- ALBA Synchrotron Light Source, NCD-SWEET Beamline, Cerdanyola del Valles, 08290, Spain
| | - Barnaby Walker
- Centre for Plastic Electronics and Department of Chemistry, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
| | - James H Bannock
- Centre for Plastic Electronics and Department of Chemistry, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
| | - John de Mello
- Centre for Plastic Electronics and Department of Chemistry, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
| | - Carlos Silva
- School of Physics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - Thuc-Quyen Nguyen
- Center for Polymers and Organic Solids, University of California, Santa Barbara, CA, 93106, USA
| | - Daniele Cangialosi
- Centro de Física de Materiales (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, San Sebastián, 20018, Spain
- Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, San Sebastián, 20018, Spain
| | - Natalie Stingelin
- School of Materials Science & Engineering and School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA, 30332, USA
- Laboratoire de Chimie des Polymères Organiques-LCPO, UMR5629 Universitéde Bordeaux, Allée Geoffroy Saint Hilaire, Pessac Cedex, 33615, France
| | - Jaime Martín
- POLYMAT, University of the Basque Country UPV/EHU, Av. de Tolosa 72, San Sebastián, 20018, Spain
- Ikerbasque, Basque Foundation for Science, Bilbao, 48013, Spain
- Universidade da Coruña, Grupo de Polímeros, Departamento de Física e Ciencias da Terra, Centro de Investigacións Tecnolóxicas (CIT), Esteiro, Ferrol, 15471, Spain
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13
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Wang H, Jin S, Zhang X, Xie Y. Excitonic Effects in Polymeric Photocatalysts. Angew Chem Int Ed Engl 2020; 59:22828-22839. [DOI: 10.1002/anie.202002241] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Indexed: 12/31/2022]
Affiliation(s)
- Hui Wang
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
- Institute of Energy Hefei Comprehensive National Science Center Hefei Anhui 230031 P. R. China
| | - Sen Jin
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
| | - Xiaodong Zhang
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
- Institute of Energy Hefei Comprehensive National Science Center Hefei Anhui 230031 P. R. China
| | - Yi Xie
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
- Institute of Energy Hefei Comprehensive National Science Center Hefei Anhui 230031 P. R. China
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14
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Affiliation(s)
- Hui Wang
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
- Institute of Energy Hefei Comprehensive National Science Center Hefei Anhui 230031 P. R. China
| | - Sen Jin
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
| | - Xiaodong Zhang
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
- Institute of Energy Hefei Comprehensive National Science Center Hefei Anhui 230031 P. R. China
| | - Yi Xie
- Hefei National Laboratory for Physical Sciences at the Microscale CAS Centre for Excellence in Nanoscience University of Science and Technology of China Hefei Anhui 230026 P. R. China
- Institute of Energy Hefei Comprehensive National Science Center Hefei Anhui 230031 P. R. China
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15
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Zhou Z, Li K, Deng W, Li J, Yan Y, Li Y, Quan X, Wang T. Nitrogen vacancy mediated exciton dissociation in carbon nitride nanosheets: Enhanced hydroxyl radicals generation for efficient photocatalytic degradation of organic pollutants. JOURNAL OF HAZARDOUS MATERIALS 2020; 387:122023. [PMID: 31927350 DOI: 10.1016/j.jhazmat.2020.122023] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Revised: 12/11/2019] [Accepted: 01/02/2020] [Indexed: 06/10/2023]
Abstract
Polymeric materials are promising candidates as photocatalysts for environmental purification, however their catalytic performance are still unsatisfactory mainly due to the strong Coulomb interactions between electron and hole that leads to fast charge recombination. Herein, taking graphitic carbon nitride as an example, we verify that installing carbon nitride nanosheets with nitrogen vacancy could break the intrinsic electronic state distribution, forming energy disordered interfaces around the vacancies with the energy difference as large as 0.35 eV. Such a large energy difference is found energetic enough to overcome the strong Coulomb interactions between electron and hole for hot electron and hole generation, as a result showing high electron-hole separation efficiency. Benefited from these advantages, the as prepared material shows remarkable photocatalytic performance toward organic pollutants degradation. The improved catalytic performance is originated from the promoted exciton dissociation that leads to ultra high hydroxyl radical generation. This study offers a new understanding of the excitonic effects for designing advanced polymeric photocatalyst for energy and environment related applications.
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Affiliation(s)
- Zhentao Zhou
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China
| | - Kexin Li
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China.
| | - Wenying Deng
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China
| | - Jun Li
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China
| | - Yinhua Yan
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China
| | - Yawen Li
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China
| | - Xiaoke Quan
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China
| | - Tong Wang
- Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, NanChang Hangkong University, NanChang 330063, People's Republic of China
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16
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Iimori T, Awasthi K, Chiou CS, Diau EWG, Ohta N. Fluorescence enhancement induced by quadratic electric-field effects on singlet exciton dynamics in poly(3-hexylthiophene) dispersed in poly(methyl methacrylate). Phys Chem Chem Phys 2019; 21:5695-5704. [PMID: 30801107 DOI: 10.1039/c8cp07801g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The dynamics of the exciton generated by photoexcitation of a regioregular poly(3-hexylthiophene) (P3HT) polymer dispersed in a poly(methyl methacrylate) (PMMA) matrix was examined using electro-photoluminescence (E-PL) spectroscopy, where electric field effects on the photoluminescence (PL) spectra were measured. The quadratic electric-field effect was investigated using the modulation technique, with field-induced changes in the PL intensity monitored at the second harmonic of the modulation frequency of the applied electric field. Absorption and PL spectra indicated the formation of both ordered crystalline aggregates and amorphous regions of P3HT polymer chains. Although previous studies of electric field effects on π-conjugated polymers have generally shown that the PL intensity is decreased by electric fields, we report that the PL intensity of P3HT and PL lifetime increased with the quadratic electric-field effect. The magnitude of the change in PL intensity was quantitatively explained in terms of the field-induced decrease in the nonradiative decay rate constants of the exciton. We proposed that a delayed PL, originating from charge carrier recombination, was enhanced in the presence of electric fields. The rate constant of the downhill relaxation process of the exciton, which originated from the relaxation in distributed energy levels due to an inherent energetic disorder in P3HT aggregates, was implied to decrease in the presence of electric fields. The radiative decay rate constant and PL quantum yield of P3HT dissolved in solution, which were evaluated from the molar extinction coefficient and the PL lifetime, were compared with those of P3HT dispersed in a PMMA matrix.
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Affiliation(s)
- Toshifumi Iimori
- Department of Applied Chemistry, Muroran Institute of Technology, Mizumoto-cho, Muroran 050-8585, Japan
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17
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Hafner RJ, Tian L, Brauer JC, Schmaltz T, Sienkiewicz A, Balog S, Flauraud V, Brugger J, Frauenrath H. Unusually Long-Lived Photocharges in Helical Organic Semiconductor Nanostructures. ACS NANO 2018; 12:9116-9125. [PMID: 30138559 DOI: 10.1021/acsnano.8b03165] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Photocharge generation and formation of long-lived charge carriers are relevant in photosynthesis, photocatalysis, photovoltaics, and organic electronics. A better understanding of the factors that determine these processes in synthetic polymer semiconductors is crucial, but difficult due to their morphological inhomogeneity. Here, we report the formation of exceptionally long-lived photocharges in one-dimensional organic semiconductor nanostructures. These nanostructures consist of chiral oligopeptide-substituted thienothiophene-based chromophores and exhibit a well-defined helical arrangement of these chromophores at their core. The chromophores give rise to spectroscopic H-aggregates and show strong intermolecular excitonic coupling. We demonstrate that all of these parameters are the prerequisites required for the nanostructures to show the efficient formation of polaron-like photocharges upon irradiation with a low-power white light source. The observed charge carriers in the helical nanowires show an unusually long lifetime on the order of several hours and are formed at high concentrations of up to 3 mol % in the absence of any dedicated electron acceptor. They are observed in solution as well as in film and furthermore give rise to a light-induced increase of the macroscopic charge transport. By contrast, no such photocharge generation is observed either in non-aggregating reference systems of the same chromophores or in aggregated but non-helical systems that do not form one-dimensional nanostructures. Our results thus demonstrate a clear correlation between nanoscopic confinement and the generation of long-lived photocharges.
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Affiliation(s)
- Regina J Hafner
- Institute of Materials, Laboratory of Macromolecular and Organic Materials , Ecole Polytechnique Fédérale de Lausanne (EPFL) , EPFL-STI-IMX-LMOM, MXG 037, Station 12 , 1015 Lausanne , Switzerland
| | - Liangfei Tian
- Institute of Materials, Laboratory of Macromolecular and Organic Materials , Ecole Polytechnique Fédérale de Lausanne (EPFL) , EPFL-STI-IMX-LMOM, MXG 037, Station 12 , 1015 Lausanne , Switzerland
| | - Jan C Brauer
- Institute of Materials, Laboratory of Macromolecular and Organic Materials , Ecole Polytechnique Fédérale de Lausanne (EPFL) , EPFL-STI-IMX-LMOM, MXG 037, Station 12 , 1015 Lausanne , Switzerland
| | - Thomas Schmaltz
- Institute of Materials, Laboratory of Macromolecular and Organic Materials , Ecole Polytechnique Fédérale de Lausanne (EPFL) , EPFL-STI-IMX-LMOM, MXG 037, Station 12 , 1015 Lausanne , Switzerland
| | | | | | | | | | - Holger Frauenrath
- Institute of Materials, Laboratory of Macromolecular and Organic Materials , Ecole Polytechnique Fédérale de Lausanne (EPFL) , EPFL-STI-IMX-LMOM, MXG 037, Station 12 , 1015 Lausanne , Switzerland
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18
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Mesomorphic Behavior in Silver(I) N-(4-Pyridyl) Benzamide with Aromatic π⁻π Stacking Counterions. MATERIALS 2018; 11:ma11091666. [PMID: 30205605 PMCID: PMC6163786 DOI: 10.3390/ma11091666] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 08/03/2018] [Accepted: 09/03/2018] [Indexed: 01/22/2023]
Abstract
Organic semiconductor materials composed of π–π stacking aromatic compounds have been under intense investigation for their potential uses in flexible electronics and other advanced technologies. Herein we report a new family of seven π–π stacking compounds of silver(I) bis-N-(4-pyridyl) benzamide with varying counterions, namely [Ag(NPBA)2]X, where NPBA is N-(4-pyridyl) benzamine, X = NO3− (1), ClO4− (2), CF3SO3− (3), PF6− (4), BF4− (5), CH3PhSO3− (6), and PhSO3− (7), which form extended π−π stacking networks in one-dimensional (1D), 2D and 3D directions in the crystalline solid-state via the phenyl moiety, with average inter-ring distances of 3.823 Å. Interestingly, the counterions that contain π–π stacking-capable groups, such as in 6 and 7, can induce the formation of mesomorphic phases at 130 °C in dimethylformamide (DMF), and can generate highly branched networks at the mesoscale. Atomic force microscopy studies showed that 2D interconnected fibers form right after nucleation, and they extend from ~30 nm in diameter grow to reach the micron scale, which suggests that it may be possible to stop the process in order to obtain nanofibers. Differential scanning calorimetry studies showed no remarkable thermal behavior in the complexes in the solid state, which suggests that the mesomorphic phases originate from the mechanisms that occur in the DMF solution at high temperatures. An all-electron level simulation of the band gaps using NRLMOL (Naval Research Laboratory Molecular Research Library) on the crystals gave 3.25 eV for (1), 3.68 eV for (2), 1.48 eV for (3), 5.08 eV for (4), 1.53 eV for (5), and 3.55 eV for (6). Mesomorphic behavior in materials containing π–π stacking aromatic interactions that also exhibit low-band gap properties may pave the way to a new generation of highly branched organic semiconductors.
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19
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Wu Z, Cui P, Zhang G, Luo Y, Jiang J. Self-Adaptive Switch Enabling Complete Charge Separation in Molecular-Based Optoelectronic Conversion. J Phys Chem Lett 2018; 9:837-843. [PMID: 29397736 DOI: 10.1021/acs.jpclett.8b00119] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Achieving high charge recombination probability has been the major challenge for the practical utilization of molecule-based solar harvesting. Molecular switches were introduced to stabilize the charge separation state in donor-acceptor systems, but it is difficult to seamlessly incorporate the ON/OFF switching actions into the optoelectronic conversion cycle. Here we present a self-adaptive system in which the donor and acceptor are bridged by a switchable moiety that enables a complete charge separation repeatedly. Calculations are presented for a platinum(II) terpyridyl complex with an azobenzene bridge. The charge transfer induced by light extracts electrons from the azobenzene group, automatically triggering a trans → cis isomerization. The resulting conformation suppresses charge recombination. Energized charges are trapped in the acceptor, ready for charge collection by electrodes. The bridge then goes through inverse isomerization to restore the conjugation and conductance. This self-adaptive design provides a novel way to improve the performance of optoelectronic conversion and realize practical solar-harvesting applications in organic molecular systems.
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Affiliation(s)
- Ziye Wu
- Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), CAS Center for Excellence in Nanoscience, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, China
| | - Peng Cui
- Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), CAS Center for Excellence in Nanoscience, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, China
| | - Guozhen Zhang
- Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), CAS Center for Excellence in Nanoscience, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, China
| | - Yi Luo
- Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), CAS Center for Excellence in Nanoscience, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, China
| | - Jun Jiang
- Hefei National Laboratory for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), CAS Center for Excellence in Nanoscience, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, China
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20
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Wang H, Yong D, Chen S, Jiang S, Zhang X, Shao W, Zhang Q, Yan W, Pan B, Xie Y. Oxygen-Vacancy-Mediated Exciton Dissociation in BiOBr for Boosting Charge-Carrier-Involved Molecular Oxygen Activation. J Am Chem Soc 2018; 140:1760-1766. [DOI: 10.1021/jacs.7b10997] [Citation(s) in RCA: 476] [Impact Index Per Article: 79.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Hui Wang
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Dingyu Yong
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Shichuan Chen
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Shenlong Jiang
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Xiaodong Zhang
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Wei Shao
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Qun Zhang
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Wensheng Yan
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Bicai Pan
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Yi Xie
- Hefei National Laboratory
for Physical Science at the Microscale, CAS Center for Excellence
in Nanoscience, iChEM, Synergetic Innovation Center of Quantum Information
and Quantum Physics, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
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21
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Feng X, Chen H, Jiang F, Wang X. Enhanced visible-light photocatalytic nitrogen fixation over semicrystalline graphitic carbon nitride: Oxygen and sulfur co-doping for crystal and electronic structure modulation. J Colloid Interface Sci 2018; 509:298-306. [DOI: 10.1016/j.jcis.2017.09.026] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 08/30/2017] [Accepted: 09/07/2017] [Indexed: 12/17/2022]
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22
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Grégoire P, Srimath Kandada AR, Vella E, Tao C, Leonelli R, Silva C. Incoherent population mixing contributions to phase-modulation two-dimensional coherent excitation spectra. J Chem Phys 2017; 147:114201. [DOI: 10.1063/1.4994987] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Pascal Grégoire
- Département de physique, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7,
Canada
| | - Ajay Ram Srimath Kandada
- Département de physique, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7,
Canada
- Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, Via Giovanni Pascoli 70/3, 20133 Milano,
Italy
- School of Chemistry and Biochemistry, School of Physics, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta,
Georgia 30332, USA
| | - Eleonora Vella
- Département de physique, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7,
Canada
| | - Chen Tao
- Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, Via Giovanni Pascoli 70/3, 20133 Milano,
Italy
| | - Richard Leonelli
- Département de physique, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7,
Canada
| | - Carlos Silva
- Département de physique, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7,
Canada
- School of Chemistry and Biochemistry, School of Physics, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta,
Georgia 30332, USA
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23
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Colella NS, Labastide JA, Cherniawski BP, Thompson HB, Marques SR, Zhang L, Usluer Ö, Watkins JJ, Briseno AL, Barnes MD. Poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] Oligomer Single-Crystal Nanowires from Supercritical Solution and Their Anisotropic Exciton Dynamics. J Phys Chem Lett 2017; 8:2984-2989. [PMID: 28605188 DOI: 10.1021/acs.jpclett.7b01128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Supercritical fluids, exhibiting a combination of liquid-like solvation power and gas-like diffusivity, are a relatively unexplored medium for processing and crystallization of oligomer and polymeric semiconductors whose optoelectronic properties critically depend on the microstructure. Here we report oligomer crystallization from the polymer organic semiconductor, poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) in supercritical hexane, yielding needle-like single crystals up to several microns in length. We characterize the crystals' photophysical properties by time- and polarization-resolved photoluminescence (TPRPL) spectroscopy. These techniques reveal two-dimensional interchromophore coupling facilitated by the high degree of π-stacking order within the crystal. Furthermore, the crystals obtained from supercritical fluid were found to be similar photophysically as the crystallites found in solution-cast thin films and distinct from solution-grown crystals that exhibited spectroscopic signatures indicative of different packing geometries.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | - Michael D Barnes
- Department of Physics, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States
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24
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Simine L, Rossky PJ. Relating Chromophoric and Structural Disorder in Conjugated Polymers. J Phys Chem Lett 2017; 8:1752-1756. [PMID: 28350467 DOI: 10.1021/acs.jpclett.7b00290] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The optoelectronic properties of amorphous conjugated polymers are sensitive to the details of the conformational disorder, and spectroscopy provides the means for structural characterization of the fragments of the chain that interact with light-"chromophores". A faithful interpretation of spectroscopic conformational signatures, however, presents a theoretical challenge. Here we investigate the relationship between the ground-state optical gaps, the properties of the excited states, and the structural features of chromophores of a single molecule poly(3-hexyl)-thiophene (P3HT) using quantum-classical atomistic simulations. Our results demonstrate that chromophoric disorder arises through the interplay between excited-state delocalization and electron-hole polarization, controlled by the torsional disorder introduced by side chains. Within this conceptual framework, we predict and explain the counterintuitive spectral behavior of P3HT, a red-shifted absorption, despite shortening of chromophores, with increasing temperature. This discussion introduces the concept of disorder-induced separation of charges in amorphous conjugated polymers.
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Affiliation(s)
- Lena Simine
- Department of Chemistry, Rice University , Houston, Texas 77005, United States
| | - Peter J Rossky
- Department of Chemistry, Rice University , Houston, Texas 77005, United States
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25
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Wang H, Sun X, Li D, Zhang X, Chen S, Shao W, Tian Y, Xie Y. Boosting Hot-Electron Generation: Exciton Dissociation at the Order–Disorder Interfaces in Polymeric Photocatalysts. J Am Chem Soc 2017; 139:2468-2473. [DOI: 10.1021/jacs.6b12878] [Citation(s) in RCA: 224] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Hui Wang
- Hefei
National Laboratory for Physical Science at the Microscale, Collaborative
Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
| | - Xianshun Sun
- Hefei
National Laboratory for Physical Science at the Microscale, Collaborative
Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
| | - Dandan Li
- Department
of Chemistry, Anhui University, Hefei, Anhui 230039, People’s Republic of China
| | - Xiaodong Zhang
- Hefei
National Laboratory for Physical Science at the Microscale, Collaborative
Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
| | - Shichuan Chen
- Hefei
National Laboratory for Physical Science at the Microscale, Collaborative
Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
| | - Wei Shao
- Hefei
National Laboratory for Physical Science at the Microscale, Collaborative
Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
| | - Yupeng Tian
- Department
of Chemistry, Anhui University, Hefei, Anhui 230039, People’s Republic of China
| | - Yi Xie
- Hefei
National Laboratory for Physical Science at the Microscale, Collaborative
Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
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26
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Peterhans L, Alloa E, Sheima Y, Vannay L, Leclerc M, Corminboeuf C, Hayes SC, Banerji N. Salt-induced thermochromism of a conjugated polyelectrolyte. Phys Chem Chem Phys 2017; 19:28853-28866. [DOI: 10.1039/c7cp02734f] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We report here the photophysical properties of a water-soluble polythiophene with cationic side-chains in PBS buffer solution.
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Affiliation(s)
- Lisa Peterhans
- Department of Chemistry
- University of Fribourg
- CH-1700 Fribourg
- Switzerland
| | - Elisa Alloa
- Department of Chemistry
- University of Cyprus
- Nicosia
- Cyprus
| | - Yauhen Sheima
- Department of Chemistry
- University of Fribourg
- CH-1700 Fribourg
- Switzerland
| | - Laurent Vannay
- Laboratory for Computational Molecular Design
- Institute of Chemical Sciences and Engineering
- Ecole Polytechnique Fédérale de Lausanne (EPFL)
- CH-1015 Lausanne
- Switzerland
| | - Mario Leclerc
- Department of Chemistry
- Université Laval
- G1K 7P4 Quebec City
- Canada
| | - Clémence Corminboeuf
- Laboratory for Computational Molecular Design
- Institute of Chemical Sciences and Engineering
- Ecole Polytechnique Fédérale de Lausanne (EPFL)
- CH-1015 Lausanne
- Switzerland
| | | | - Natalie Banerji
- Department of Chemistry
- University of Fribourg
- CH-1700 Fribourg
- Switzerland
- Department of Chemistry and Biochemistry
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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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28
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Marin DM, Castaneda J, Kaushal M, Kaouk G, Jones DS, Walter MG. Spatially resolved micro-photoluminescence imaging of porphyrin single crystals. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2016.06.057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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29
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Bhattacharjee U, Elshobaki M, Santra K, Bobbitt JM, Chaudhary S, Smith EA, Petrich JW. Characterizing Electric Field Exposed P3HT Thin Films Using Polarized-Light Spectroscopies. MACROMOL CHEM PHYS 2016. [DOI: 10.1002/macp.201600113] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Ujjal Bhattacharjee
- Department of Chemistry; Iowa State University; Ames IA 50011 USA
- U.S. Department of Energy Ames Laboratory; Ames IA 50011 USA
| | | | - Kalyan Santra
- Department of Chemistry; Iowa State University; Ames IA 50011 USA
- U.S. Department of Energy Ames Laboratory; Ames IA 50011 USA
| | - Jonathan M. Bobbitt
- Department of Chemistry; Iowa State University; Ames IA 50011 USA
- U.S. Department of Energy Ames Laboratory; Ames IA 50011 USA
| | - Sumit Chaudhary
- Materials Science and Engineering Department; Iowa State University; Ames IA 50011 USA
| | - Emily A. Smith
- Department of Chemistry; Iowa State University; Ames IA 50011 USA
- U.S. Department of Energy Ames Laboratory; Ames IA 50011 USA
| | - Jacob W. Petrich
- Department of Chemistry; Iowa State University; Ames IA 50011 USA
- U.S. Department of Energy Ames Laboratory; Ames IA 50011 USA
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30
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Directional charge separation in isolated organic semiconductor crystalline nanowires. Nat Commun 2016; 7:10629. [PMID: 26912040 PMCID: PMC4773394 DOI: 10.1038/ncomms10629] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 01/06/2016] [Indexed: 01/18/2023] Open
Abstract
One of the fundamental design paradigms in organic photovoltaic device engineering is based on the idea that charge separation is an extrinsically driven process requiring an interface for exciton fission. This idea has driven an enormous materials science engineering effort focused on construction of domain sizes commensurate with a nominal exciton diffusion length of order 10 nm. Here, we show that polarized optical excitation of isolated pristine crystalline nanowires of a small molecule n-type organic semiconductor, 7,8,15,16-tetraazaterrylene, generates a significant population of charge-separated polaron pairs along the π-stacking direction. Charge separation was signalled by pronounced power-law photoluminescence decay polarized along the same axis. In the transverse direction, we observed exponential decay associated with excitons localized on individual monomers. We propose that this effect derives from an intrinsic directional charge-transfer interaction that can ultimately be programmed by molecular packing geometry. Photo-induced charge separation in organic semiconductors usually occurs at interfaces between electron donors and acceptors. Here, the authors show using photoluminescence measurements that charge separation is intrinsic and directional in organic crystalline nanowires made of stacked monomers.
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31
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Cappel UB, Moia D, Bruno A, Vaissier V, Haque SA, Barnes PRF. Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces. Sci Rep 2016; 6:21276. [PMID: 26891851 PMCID: PMC4759562 DOI: 10.1038/srep21276] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 01/18/2016] [Indexed: 01/09/2023] Open
Abstract
Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures.
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Affiliation(s)
- Ute B. Cappel
- Department of Chemistry, Imperial College London, SW7 2AZ, UK
| | - Davide Moia
- Department of Physics, Imperial College London, SW7 2AZ, UK
| | - Annalisa Bruno
- Department of Chemistry, Imperial College London, SW7 2AZ, UK
- Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Portici (Naples), Italy
| | - Valerie Vaissier
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts avenue, Cambridge, MA 02139, USA
| | - Saif A. Haque
- Department of Chemistry, Imperial College London, SW7 2AZ, UK
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32
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Grußmayer KS, Steiner F, Lupton JM, Herten DP, Vogelsang J. Differentiation between Shallow and Deep Charge Trap States on Single Poly(3-hexylthiophene) Chains through Fluorescence Photon Statistics. Chemphyschem 2015; 16:3578-83. [DOI: 10.1002/cphc.201500719] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Indexed: 01/19/2023]
Affiliation(s)
- Kristin S. Grußmayer
- CellNetworks Cluster und Physikalisch-Chemisches Institut; Universität Heidelberg; Im Neuenheimer Feld 267 69210 Heidelberg Germany
| | - Florian Steiner
- Institut für Experimentelle und Angewandte Physik; Universität Regensburg; Universitätsstrasse 31 93053 Regensburg Germany
| | - John M. Lupton
- Institut für Experimentelle und Angewandte Physik; Universität Regensburg; Universitätsstrasse 31 93053 Regensburg Germany
| | - Dirk-Peter Herten
- CellNetworks Cluster und Physikalisch-Chemisches Institut; Universität Heidelberg; Im Neuenheimer Feld 267 69210 Heidelberg Germany
| | - Jan Vogelsang
- Institut für Experimentelle und Angewandte Physik; Universität Regensburg; Universitätsstrasse 31 93053 Regensburg Germany
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33
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Cochrane KA, Schiffrin A, Roussy TS, Capsoni M, Burke SA. Pronounced polarization-induced energy level shifts at boundaries of organic semiconductor nanostructures. Nat Commun 2015; 6:8312. [PMID: 26440933 PMCID: PMC4600718 DOI: 10.1038/ncomms9312] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Accepted: 08/11/2015] [Indexed: 11/09/2022] Open
Abstract
Organic semiconductor devices rely on the movement of charge at and near interfaces, making an understanding of energy level alignment at these boundaries an essential element of optimizing materials for electronic and optoelectronic applications. Here we employ low temperature scanning tunneling microscopy and spectroscopy to investigate a model system: two-dimensional nanostructures of the prototypical organic semiconductor, PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) adsorbed on NaCl (2 ML)/Ag(111). Pixel-by-pixel scanning tunneling spectroscopy allows mapping of occupied and unoccupied electronic states across these nanoislands with sub-molecular spatial resolution, revealing strong electronic differences between molecules at the edges and those in the centre, with energy level shifts of up to 400 meV. We attribute this to the change in electrostatic environment at the boundaries of clusters, namely via polarization of neighbouring molecules. The observation of these strong shifts illustrates a crucial issue: interfacial energy level alignment can differ substantially from the bulk electronic structure in organic materials. Interfaces are essential in organic semiconductor devices, yet the detailed connection between interface geometry and energy level alignment are not fully understood. Here, Cochrane et al. quantify energy level shifts with sub-molecular resolution within a nanoscale model organic semiconductor system.
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Affiliation(s)
- K A Cochrane
- Department of Chemistry, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1
| | - A Schiffrin
- Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.,Quantum Matter Institute, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z4
| | - T S Roussy
- Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1
| | - M Capsoni
- Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1
| | - S A Burke
- Department of Chemistry, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.,Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.,Quantum Matter Institute, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z4
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34
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Hu Z, Willard AP, Ono RJ, Bielawski CW, Rossky PJ, Vanden Bout DA. An insight into non-emissive excited states in conjugated polymers. Nat Commun 2015; 6:8246. [PMID: 26391514 PMCID: PMC4595598 DOI: 10.1038/ncomms9246] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2014] [Accepted: 08/03/2015] [Indexed: 11/25/2022] Open
Abstract
Conjugated polymers in the solid state usually exhibit low fluorescence quantum yields, which limit their applications in many areas such as light-emitting diodes. Despite considerable research efforts, the underlying mechanism still remains controversial and elusive. Here, the nature and properties of excited states in the archetypal polythiophene are investigated via aggregates suspended in solvents with different dielectric constants (ɛ). In relatively polar solvents (ɛ>∼ 3), the aggregates exhibit a low fluorescence quantum yield (QY) of 2–5%, similar to bulk films, however, in relatively nonpolar solvents (ɛ<∼ 3) they demonstrate much higher fluorescence QY up to 20–30%. A series of mixed quantum-classical atomistic simulations illustrate that dielectric induced stabilization of nonradiative charge-transfer (CT) type states can lead to similar drastic reduction in fluorescence QY as seen experimentally. Fluorescence lifetime measurement reveals that the CT-type states exist as a competitive channel of the formation of emissive exciton-type states. Conjugated polymers in thin films exhibit low fluorescence quantum yields, but the mechanism is still unclear. Here, Hu et al. show the trade-off between charge transfer and emissive exciton states, whilst the former can be suppressed via dielectric-induced stabilization for large fluorescence quantum yields.
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Affiliation(s)
- Zhongjian Hu
- Center for Nano- and Molecular Science and Technology, Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Adam P Willard
- Center for Nano- and Molecular Science and Technology, Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Robert J Ono
- Center for Nano- and Molecular Science and Technology, Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Christopher W Bielawski
- Center for Nano- and Molecular Science and Technology, Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - Peter J Rossky
- Center for Nano- and Molecular Science and Technology, Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
| | - David A Vanden Bout
- Center for Nano- and Molecular Science and Technology, Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA
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35
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Huber RC, Ferreira AS, Thompson R, Kilbride D, Knutson NS, Devi LS, Toso DB, Challa JR, Zhou ZH, Rubin Y, Schwartz BJ, Tolbert SH. POLARON DYNAMICS. Long-lived photoinduced polaron formation in conjugated polyelectrolyte-fullerene assemblies. Science 2015; 348:1340-3. [PMID: 26089510 PMCID: PMC6039100 DOI: 10.1126/science.aaa6850] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The efficiency of biological photosynthesis results from the exquisite organization of photoactive elements that promote rapid movement of charge carriers out of a critical recombination range. If synthetic organic photovoltaic materials could mimic this assembly, charge separation and collection could be markedly enhanced. We show that micelle-forming cationic semiconducting polymers can coassemble in water with cationic fullerene derivatives to create photoinduced electron-transfer cascades that lead to exceptionally long-lived polarons. The stability of the polarons depends on the organization of the polymer-fullerene assembly. Properly designed assemblies can produce separated polaronic charges that are stable for days or weeks in aqueous solution.
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Affiliation(s)
- Rachel C Huber
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA
| | - Amy S Ferreira
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA
| | - Robert Thompson
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA
| | - Daniel Kilbride
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA
| | - Nicholas S Knutson
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA
| | - Lekshmi Sudha Devi
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA
| | - Daniel B Toso
- Department of Microbiology, Immunology and Molecular Genetics, and the Biomedical Engineering Program, UCLA, Los Angeles, CA 90095, USA
| | - J Reddy Challa
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA
| | - Z Hong Zhou
- Department of Microbiology, Immunology and Molecular Genetics, and the Biomedical Engineering Program, UCLA, Los Angeles, CA 90095, USA. The California NanoSystems Institute (CNSI), UCLA, Los Angeles, CA 90095, USA
| | - Yves Rubin
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA.
| | - Benjamin J Schwartz
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA. The California NanoSystems Institute (CNSI), UCLA, Los Angeles, CA 90095, USA.
| | - Sarah H Tolbert
- Department of Chemistry and Biochemistry, University of California-Los Angeles (UCLA), Los Angeles, CA 90095-1569, USA. The California NanoSystems Institute (CNSI), UCLA, Los Angeles, CA 90095, USA. Department of Materials Science and Engineering, UCLA, Los Angeles, CA 90095, USA.
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36
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Di Nuzzo D, Viola D, Fischer FSU, Cerullo G, Ludwigs S, Da Como E. Enhanced Photogeneration of Polaron Pairs in Neat Semicrystalline Donor-Acceptor Copolymer Films via Direct Excitation of Interchain Aggregates. J Phys Chem Lett 2015; 6:1196-1203. [PMID: 26262971 DOI: 10.1021/acs.jpclett.5b00218] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We investigate the photogeneration of polaron pairs (PPs) in neat films of the semicrystalline donor-acceptor semiconducting copolymer PCPDTBT. Carefully selecting the solution-processing procedures, we obtain films with different amounts of crystallinity and interchain aggregation. We compare the photogeneration of PPs between the films by monitoring their photoinduced absorption in ultrafast pump-probe experiments, selectively exciting nonaggregated or aggregated polymer chains. The direct photoexcitation of interchain π-aggregates results in prompt (<100 fs) charge generation. Compared to the case where nonaggregated chains are excited, we find an 8-fold increase in the prompt PP to singlet-exciton ratio. We also show that highly crystalline lamellar nanostructures not containing π-stacked or any light-absorbing aggregates do not improve the efficiency of PP photogeneration. Our results show that light absorption from interchain aggregates is highly beneficial for charge photogeneration in semiconducting polymers and should be taken into account when optimizing film morphologies for photovoltaic devices.
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Affiliation(s)
- Daniele Di Nuzzo
- †Department of Physics, University of Bath, BA2 7AY Bath, United Kingdom
| | - Daniele Viola
- ‡Dipartimento di Fisica, IFN-CNR, Politecnico di Milano, 20133 Milano, Italy
| | - Florian S U Fischer
- §IPOC-Functional Polymers, University of Stuttgart, 70569 Stuttgart, Germany
| | - Giulio Cerullo
- ‡Dipartimento di Fisica, IFN-CNR, Politecnico di Milano, 20133 Milano, Italy
| | - Sabine Ludwigs
- §IPOC-Functional Polymers, University of Stuttgart, 70569 Stuttgart, Germany
| | - Enrico Da Como
- †Department of Physics, University of Bath, BA2 7AY Bath, United Kingdom
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37
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Panzer F, Sommer M, Bässler H, Thelakkat M, Köhler A. Spectroscopic Signature of Two Distinct H-Aggregate Species in Poly(3-hexylthiophene). Macromolecules 2015. [DOI: 10.1021/acs.macromol.5b00129] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Fabian Panzer
- Experimental Physics II, ‡Bayreuth Institute of Macromolecular
Research (BIMF), and §Applied Functional
Polymers, Macromolecular Chemistry I, University of Bayreuth, 95540 Bayreuth, Germany
| | - Michael Sommer
- Experimental Physics II, ‡Bayreuth Institute of Macromolecular
Research (BIMF), and §Applied Functional
Polymers, Macromolecular Chemistry I, University of Bayreuth, 95540 Bayreuth, Germany
| | - Heinz Bässler
- Experimental Physics II, ‡Bayreuth Institute of Macromolecular
Research (BIMF), and §Applied Functional
Polymers, Macromolecular Chemistry I, University of Bayreuth, 95540 Bayreuth, Germany
| | - Mukundan Thelakkat
- Experimental Physics II, ‡Bayreuth Institute of Macromolecular
Research (BIMF), and §Applied Functional
Polymers, Macromolecular Chemistry I, University of Bayreuth, 95540 Bayreuth, Germany
| | - Anna Köhler
- Experimental Physics II, ‡Bayreuth Institute of Macromolecular
Research (BIMF), and §Applied Functional
Polymers, Macromolecular Chemistry I, University of Bayreuth, 95540 Bayreuth, Germany
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38
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Thomas AK, Garcia JA, Ulibarri-Sanchez J, Gao J, Grey JK. High intrachain order promotes triplet formation from recombination of long-lived polarons in poly(3-hexylthiophene) J-aggregate nanofibers. ACS NANO 2014; 8:10559-68. [PMID: 25285851 DOI: 10.1021/nn5040026] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Photoluminescence (PL) of single poly(3-hexylthiophene) (P3HT) J-aggregate nanofibers (NFs) exhibits strong quenching under intensity-modulated pulsed excitation. Initial PL intensities (I(0)) decay to steady-state levels (ISS) typically within ∼ 1-10 μs, and large quenching depths (I(0)/I(SS) >2) are observed for ∼ 70% of these NFs. Similar studies of polymorphic, H-aggregate type P3HT NFs show much smaller PL quenching depths (I(0)/I(SS) ≤ 1.2). P3HT chains in J-type NF π-stacks possess high intrachain order, which has been shown previously to promote the formation of long-lived, delocalized polarons. We propose that these species recombine nongeminately to triplets on time scales of >1 ns. The identity of triplets as the dominant PL quenchers was confirmed by subjecting NFs to oxygen, resulting in an instantaneous loss of triplet PL quenching (I(0)/I(SS) ∼ 1). The lower intrachain order in H-type NFs, similar to P3HT thin-film aggregates, localizes excitons and polarons, leading to efficient geminate recombination that suppresses triplet formation at longer time scales. Our results demonstrate the promise of self-assembly strategies to control intrachain ordering within multichromophoric polymeric aggregate assemblies to tune exciton coupling and interconversion processes between different spin states.
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Affiliation(s)
- Alan K Thomas
- Department of Chemistry and Chemical Biology, University of New Mexico , MSC03 2060, Albuquerque, New Mexico 87131, United States
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39
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Song Y, Clafton SN, Pensack RD, Kee TW, Scholes GD. Vibrational coherence probes the mechanism of ultrafast electron transfer in polymer–fullerene blends. Nat Commun 2014; 5:4933. [DOI: 10.1038/ncomms5933] [Citation(s) in RCA: 113] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 08/01/2014] [Indexed: 12/18/2022] Open
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40
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Barker AJ, Chen K, Hodgkiss JM. Distance distributions of photogenerated charge pairs in organic photovoltaic cells. J Am Chem Soc 2014; 136:12018-26. [PMID: 25102389 DOI: 10.1021/ja505380j] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Strong Coulomb interactions in organic photovoltaic cells dictate that charges must separate over relatively long distances in order to circumvent geminate recombination and produce photocurrent. In this article, we measure the distance distributions of thermalized charge pairs by accessing a regime at low temperature where charge pairs are frozen out following the primary charge separation step and recombine monomolecularly via tunneling. The exponential attenuation of tunneling rate with distance provides a sensitive probe of the distance distribution of primary charge pairs, reminiscent of electron transfer studies in proteins. By fitting recombination dynamics to distributions of recombination rates, we identified populations of charge-transfer states and well-separated charge pairs. For the wide range of materials we studied, the yield of separated charges in the tunneling regime is strongly correlated with the yield of free charges measured via their intensity-dependent bimolecular recombination dynamics at room temperature. We therefore conclude that populations of free charges are established via long-range charge separation within the thermalization time scale, thus invoking early branching between free and bound charges across an energetic barrier. Subject to assumed values of the electron tunneling attenuation constant, we estimate critical charge separation distances of ∼3-4 nm in all materials. In some blends, large fullerene crystals can enhance charge separation yields; however, the important role of the polymers is also highlighted in blends that achieved significant charge separation with minimal fullerene concentration. We expect that our approach of isolating the intrinsic properties of primary charge pairs will be of considerable value in guiding new material development and testing the validity of proposed mechanisms for long-range charge separation.
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Affiliation(s)
- Alex J Barker
- The MacDiarmid Institute for Advanced Materials and Nanotechnology , Wellington 6140, New Zealand
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Abstract
Emerging photovoltaic devices based on molecular and nanomaterials are mostly excitonic in nature. The initial absorption of a photon in these materials creates an exciton that can subsequently dissociate in each material or at their interfaces to give charge carriers. Any attempt at mechanistic understanding of excitonic solar cells must start with drawing energy level diagrams. This seemingly elementary exercise, which is described in textbooks for inorganic solar cells, has turned out to be a difficult subject in the literature. The problem stems from conceptual confusion of single-particle energy with quasi-particle energy and the misleading practice of mixing the two on the same energy level diagram. Here, I discuss how to draw physically accurate energy diagrams in excitonic solar cells using only single-particle energies (ionization potentials and electron affinities) of both ground and optically excited states. I will briefly discuss current understanding on the electronic energy landscape responsible for efficient charge separation in excitonic solar cells.
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Affiliation(s)
- X-Y Zhu
- Department of Chemistry, Columbia University, New York, New York 10027, United States
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Botiz I, Freyberg P, Leordean C, Gabudean AM, Astilean S, Yang ACM, Stingelin N. Enhancing the photoluminescence emission of conjugated MEH-PPV by light processing. ACS APPLIED MATERIALS & INTERFACES 2014; 6:4974-4979. [PMID: 24611888 DOI: 10.1021/am4060244] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We show here that treatment of thin films of conjugated polymers by illumination with light leads to an increase of the intensity of their photoluminescence by up to 42%. The corresponding enhancement of absorbance was much less pronounced. We explain this significant enhancement of photoluminescence by a planarization of the conjugated polymer chains induced by photoexcitations even below the glass transition temperature, possibly due to an increased conjugation length. Interestingly, the photoluminescence remains at the enhanced level for more than 71 h after treatment of the films by illumination with light, likely due to the fact that below the glass transition temperature no restoring force could return the conjugated chains into their initial conformational state.
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Affiliation(s)
- Ioan Botiz
- Freiburg Institute for Advanced Studies , Albertstraße 19, Freiburg 79104, Germany
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Influence of Molecular Conformations and Microstructure on the Optoelectronic Properties of Conjugated Polymers. MATERIALS 2014; 7:2273-2300. [PMID: 28788568 PMCID: PMC5453253 DOI: 10.3390/ma7032273] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Revised: 03/03/2014] [Accepted: 03/07/2014] [Indexed: 12/23/2022]
Abstract
It is increasingly obvious that the molecular conformations and the long-range arrangement that conjugated polymers can adopt under various experimental conditions in bulk, solutions or thin films, significantly impact their resulting optoelectronic properties. As a consequence, the functionalities and efficiencies of resulting organic devices, such as field-effect transistors, light-emitting diodes, or photovoltaic cells, also dramatically change due to the close structure/property relationship. A range of structure/optoelectronic properties relationships have been investigated over the last few years using various experimental and theoretical methods, and, further, interesting correlations are continuously revealed by the scientific community. In this review, we discuss the latest findings related to the structure/optoelectronic properties interrelationships that exist in organic devices fabricated with conjugated polymers in terms of charge mobility, absorption, photoluminescence, as well as photovoltaic properties.
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Tamai Y, Matsuura Y, Ohkita H, Benten H, Ito S. One-Dimensional Singlet Exciton Diffusion in Poly(3-hexylthiophene) Crystalline Domains. J Phys Chem Lett 2014; 5:399-403. [PMID: 26270718 DOI: 10.1021/jz402299a] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Singlet exciton dynamics in crystalline domains of regioregular poly(3-hexylthiophene) (P3HT) films was studied by transient absorption spectroscopy. Upon the selective excitation of crystalline P3HT at the absorption edge, no red shift of the singlet exciton band was observed with an elapse of time, suggesting singlet exciton dynamics in relatively homogeneous P3HT crystalline domains without downhill relaxation in the energetic disorder. Even under such selective excitation conditions, the annihilation rate coefficient γ(t) was still dependent on time, γ(t) ∝ t(-1/2), which is attributed to anisotropic exciton diffusion in P3HT crystalline domains. From the annihilation rate coefficient, the singlet exciton diffusion coefficient D and exciton diffusion length LD in the crystalline domains were evaluated to be 7.9 × 10(-3) cm(2) s(-1) and 20 nm, respectively. The origin of the time-dependent exciton dynamics is discussed in terms of dimensionality.
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Affiliation(s)
- Yasunari Tamai
- †Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan
| | - Yuu Matsuura
- †Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan
| | - Hideo Ohkita
- †Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan
- ‡Japan Science and Technology Agency (JST), PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Hiroaki Benten
- †Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan
| | - Shinzaburo Ito
- †Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto 615-8510, Japan
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Abstract
Aggregates of conjugated polymers exhibit two classes of fundamental electronic interactions: those occurring within a given chain and those occurring between chains. The impact of such excitonic interactions on the photophysics of polymer films can be understood using concepts of J- and H-aggregation originally developed by Kasha and coworkers to treat aggregates of small molecules. In polymer assemblies, intrachain through-bond interactions lead to J-aggregate behavior, whereas interchain Coulombic interactions lead to H-aggregate behavior. The photophysics of common emissive conjugated polymer films are determined by a competition between intrachain, J-favoring interactions and interchain, H-favoring interactions. We review formalisms describing absorption and photoluminescence lineshapes, based on intra- and intermolecular excitonic coupling, electron-vibrational coupling, and correlated energetic disorder. Examples include regioregular polythiophenes, pheneylene-vinylenes, and polydiacetylene.
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Affiliation(s)
- Frank C Spano
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122;
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Chen K, Barker AJ, Reish ME, Gordon KC, Hodgkiss JM. Broadband ultrafast photoluminescence spectroscopy resolves charge photogeneration via delocalized hot excitons in polymer:fullerene photovoltaic blends. J Am Chem Soc 2013; 135:18502-12. [PMID: 24206394 DOI: 10.1021/ja408235h] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Conventional descriptions of excitons in semiconducting polymers do not account for several important observations in polymer:fullerene photovoltaic blends, including the ultrafast time scale of charge photogeneration in phase separated blends and the intermediate role of delocalized charge transfer states. We investigate the nature of excitons in thin films of polymers and polymer:fullerene blends by using broadband ultrafast photoluminescence spectroscopy. Our technique enables us to resolve energetic relaxation, as well as the volume of excitons and population dynamics on ultrafast time scales. We resolve substantial high-energy emission from hot excitons prior to energetic relaxation, which occurs predominantly on a subpicosecond time scale. Consistent with quantum chemical calculations, ultrafast annihilation measurements show that excitons initially extend along a substantial chain length prior to localization induced by structural relaxation. Moreover, we see that hot excitons are initially highly mobile and the subsequent rapid decay in mobility is correlated with energetic relaxation. The relevance of these measurements to charge photogeneration is confirmed by our measurements in blends. We find that charge photogeneration occurs predominately via these delocalized hot exciton states in competition with relaxation and independently of temperature. As well as accounting for the ultrafast time scale of charge generation across large polymer phases, delocalized hot excitons may also account for the crucial requirement that primary charge pairs are well separated in efficient organic photovoltaic blends.
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Affiliation(s)
- Kai Chen
- The MacDiarmid Institute for Advanced Materials and Nanotechnology , New Zealand
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Barrett HP, Kennedy WJ, Boucher DS. Spectroscopic characterization of P3HT/SWNT composites synthesized using in situ
GRIM methods: Improved polymer ordering via nanoscaffolding. ACTA ACUST UNITED AC 2013. [DOI: 10.1002/polb.23407] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Hayden P. Barrett
- Department of Chemistry and Biochemistry; School of Sciences and Mathematics, College of Charleston; Charleston South Carolina 29424
| | - W. Joshua Kennedy
- Materials and Processes Branch, Structural Engineering Division; NASA Johnson Space Center; Houston Texas 77058
| | - David S. Boucher
- Department of Chemistry and Biochemistry; School of Sciences and Mathematics, College of Charleston; Charleston South Carolina 29424
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Abstract
The spectral breadth of conjugated polymers gives these materials a clear advantage over other molecular compounds for organic photovoltaic applications and is a key factor in recent efficiencies topping 10%. However, why do excitonic transitions, which are inherently narrow, lead to absorption over such a broad range of wavelengths in the first place? Using single-molecule spectroscopy, we address this fundamental question in a model material, poly(3-hexylthiophene). Narrow zero-phonon lines from single chromophores are found to scatter over 200 nm, an unprecedented inhomogeneous broadening that maps the ensemble. The giant red shift between solution and bulk films arises from energy transfer to the lowest-energy chromophores in collapsed polymer chains that adopt a highly ordered morphology. We propose that the extreme energetic disorder of chromophores is structural in origin. This structural disorder on the single-chromophore level may actually enable the high degree of polymer chain ordering found in bulk films: both structural order and disorder are crucial to materials physics in devices.
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Gao J, Grey JK. Resonance Raman overtones reveal vibrational displacements and dynamics of crystalline and amorphous poly(3-hexylthiophene) chains in fullerene blends. J Chem Phys 2013; 139:044903. [DOI: 10.1063/1.4815819] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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