1
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Georgiou K, Athanasiou M, Jayaprakash R, Lidzey DG, Itskos G, Othonos A. Strong coupling in mechanically flexible free-standing organic membranes. J Chem Phys 2023; 159:234303. [PMID: 38112504 DOI: 10.1063/5.0178144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Accepted: 11/22/2023] [Indexed: 12/21/2023] Open
Abstract
Strong coupling of a confined optical field to the excitonic or vibronic transitions of a molecular material results in the formation of new hybrid states called polaritons. Such effects have been extensively studied in Fabry-Pèrot microcavity structures where an organic material is placed between two highly reflective mirrors. Recently, theoretical and experimental evidence has suggested that strong coupling can be used to modify chemical reactivity as well as molecular photophysical functionalities. However, the geometry of conventional microcavity structures limits the ability of molecules "encapsulated" in a cavity to interact with their local environment. Here, we fabricate mirrorless organic membranes that utilize the refractive index contrast between the organic active material and its surrounding medium to confine an optical field with Q-factor values up to 33. Using angle-resolved white light reflectivity measurements, we confirm that our structures operate in the strong coupling regime, with Rabi-splitting energies between 60 and 80 meV in the different structures studied. The experimental results are matched by transfer matrix and coupled oscillator models that simulate the various polariton states of the free standing membranes. Our work demonstrates that mechanically flexible and easy-to-fabricate free standing membranes can support strong light-matter coupling, making such simple and versatile structures highly promising for a range of polariton applications.
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Affiliation(s)
- Kyriacos Georgiou
- Department of Physics, Laboratory of Ultrafast Science, University of Cyprus, Nicosia 1678, Cyprus
| | - Modestos Athanasiou
- Department of Physics, Experimental Condensed Matter Physics Laboratory, University of Cyprus, Nicosia 1678, Cyprus
| | - Rahul Jayaprakash
- Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, United Kingdom
| | - David G Lidzey
- Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, United Kingdom
| | - Grigorios Itskos
- Department of Physics, Experimental Condensed Matter Physics Laboratory, University of Cyprus, Nicosia 1678, Cyprus
| | - Andreas Othonos
- Department of Physics, Laboratory of Ultrafast Science, University of Cyprus, Nicosia 1678, Cyprus
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2
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Lowrie W, Westbrook RJE, Guo J, Gonev HI, Marin-Beloqui J, Clarke TM. Organic photovoltaics: The current challenges. J Chem Phys 2023; 158:110901. [PMID: 36948814 DOI: 10.1063/5.0139457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/17/2023] Open
Abstract
Organic photovoltaics are remarkably close to reaching a landmark power conversion efficiency of 20%. Given the current urgent concerns regarding climate change, research into renewable energy solutions is crucially important. In this perspective article, we highlight several key aspects of organic photovoltaics, ranging from fundamental understanding to implementation, that need to be addressed to ensure the success of this promising technology. We cover the intriguing ability of some acceptors to undergo efficient charge photogeneration in the absence of an energetic driving force and the effects of the resulting state hybridization. We explore one of the primary loss mechanisms of organic photovoltaics-non-radiative voltage losses-and the influence of the energy gap law. Triplet states are becoming increasingly relevant owing to their presence in even the most efficient non-fullerene blends, and we assess their role as both a loss mechanism and a potential strategy to enhance efficiency. Finally, two ways in which the implementation of organic photovoltaics can be simplified are addressed. The standard bulk heterojunction architecture could be superseded by either single material photovoltaics or sequentially deposited heterojunctions, and the attributes of both are considered. While several important challenges still lie ahead for organic photovoltaics, their future is, indeed, bright.
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Affiliation(s)
- William Lowrie
- Department of Chemistry, University College London, Christopher Ingold Building, London WC1H 0AJ, United Kingdom
| | - Robert J E Westbrook
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
| | - Junjun Guo
- Department of Chemistry, University College London, Christopher Ingold Building, London WC1H 0AJ, United Kingdom
| | - Hristo Ivov Gonev
- Department of Chemistry, University College London, Christopher Ingold Building, London WC1H 0AJ, United Kingdom
| | - Jose Marin-Beloqui
- Departamento de Química Física, Universidad de Malaga, Campus Teatinos s/n, 29071 Málaga, Spain
| | - Tracey M Clarke
- Department of Chemistry, University College London, Christopher Ingold Building, London WC1H 0AJ, United Kingdom
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3
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Unraveling complex performance-limiting factors of brominated ITIC derivative: PM6 organic solar cells by using time-resolved measurements. Polym J 2022. [DOI: 10.1038/s41428-022-00704-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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4
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Upreti T, Tormann C, Kemerink M. Can Organic Solar Cells Beat the Near-Equilibrium Thermodynamic Limit? J Phys Chem Lett 2022; 13:6514-6519. [PMID: 35822430 PMCID: PMC9310094 DOI: 10.1021/acs.jpclett.2c01565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Despite an impressive increase over the past decade, experimentally determined power conversion efficiencies of organic photovoltaic cells still fall considerably below the theoretical upper bound for near-equilibrium solar cells. Even in otherwise optimized devices, a prominent yet incompletely understood loss channel is the thermalization of photogenerated charge carriers in the density of states that is broadened by energetic disorder. Here, we demonstrate by extensive numerical modeling how this loss channel can be mitigated in carefully designed morphologies. Specifically, we show how funnel-shaped donor- and acceptor-rich domains in the phase-separated morphology that are characteristic of organic bulk heterojunction solar cells can promote directed transport of positive and negative charge carriers toward the anode and cathode, respectively. We demonstrate that in optimized funnel morphologies this kinetic, nonequilibrium effect, which is boosted by the slow thermalization of photogenerated charges, allows one to surpass the near-equilibrium limit for the same material in the absence of gradients.
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Affiliation(s)
- Tanvi Upreti
- Complex
Materials and Devices, Department of Physics, Chemistry and Biology
(IFM), Linköping University, 581 83 Linköping, Sweden
- Centre
for Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany
| | - Constantin Tormann
- Centre
for Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany
| | - Martijn Kemerink
- Complex
Materials and Devices, Department of Physics, Chemistry and Biology
(IFM), Linköping University, 581 83 Linköping, Sweden
- Centre
for Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany
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5
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Upreti T, Wilken S, Zhang H, Kemerink M. Slow Relaxation of Photogenerated Charge Carriers Boosts Open-Circuit Voltage of Organic Solar Cells. J Phys Chem Lett 2021; 12:9874-9881. [PMID: 34609870 PMCID: PMC8521526 DOI: 10.1021/acs.jpclett.1c02235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Accepted: 09/23/2021] [Indexed: 06/13/2023]
Abstract
Among the parameters determining the efficiency of an organic solar cell, the open-circuit voltage (VOC) is the one with most room for improvement. Existing models for the description of VOC assume that photogenerated charge carriers are thermalized. Here, we demonstrate that quasi-equilibrium concepts cannot fully describe VOC of disordered organic devices. For two representative donor:acceptor blends, it is shown that VOC is actually 0.1-0.2 V higher than it would be if the system was in thermodynamic equilibrium. Extensive numerical modeling reveals that the excess energy is mainly due to incomplete relaxation in the disorder-broadened density of states. These findings indicate that organic solar cells work as nonequilibrium devices, in which part of the photon excess energy is harvested in the form of an enhanced VOC.
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Affiliation(s)
- Tanvi Upreti
- Complex
Materials and Devices, Department of Physics, Chemistry and Biology
(IFM), Linköping University, 581 83 Linköping, Sweden
- Centre
for Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany
| | - Sebastian Wilken
- Complex
Materials and Devices, Department of Physics, Chemistry and Biology
(IFM), Linköping University, 581 83 Linköping, Sweden
- Physics,
Faculty of Science and Engineering, Åbo
Akademi University, Porthansgatan 3, 20500 Turku, Finland
| | - Huotian Zhang
- Biomolecular
and Organic Electronics, Department of Physics, Chemistry and Biology
(IFM), Linköping University, 581 83 Linköping, Sweden
| | - Martijn Kemerink
- Complex
Materials and Devices, Department of Physics, Chemistry and Biology
(IFM), Linköping University, 581 83 Linköping, Sweden
- Centre
for Advanced Materials, Heidelberg University, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany
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6
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Hamada F, Saeki A. Mobility Relaxation of Holes and Electrons in Polymer:Fullerene and Polymer : Non-Fullerene Acceptor Solar Cells. CHEMSUSCHEM 2021; 14:3528-3534. [PMID: 33847041 DOI: 10.1002/cssc.202100566] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Revised: 04/09/2021] [Indexed: 06/12/2023]
Abstract
A non-fullerene small molecular acceptor (NFA) is a prominent molecule that shows moderate electron mobility and a narrow bandgap complementary to middle-bandgap p-type conjugated polymers, which leads to great improvement in the performance of organic photovoltaic (OPV) cells. However, little is known about the relaxation of charge carriers, which is key to efficient charge transport. Simultaneous time-of-flight (TOF) and time-resolved microwave conductivity (TRMC) measurements have been carried out on benzodithiophene-based polymer (PBDB-T):soluble C70 -fullerere (PCBM) and PBDB-T:NFA (ITIC or Y6) blends, as benchmark systems. In addition to the conventional TOF mobilities, relaxation of the hole and electron mobility are evaluated by TRMC under an external electric field. PBDB-T : ITIC exhibits much faster relaxation than PBDB-T : PCBM, whereas that in PBDB-T : Y6 is moderate. This is consistent with the energetic disorder estimated from the photoabsorption onset. Interestingly, the slower relaxation of the electrons compared to the holes in PBDB-T : Y6 is in line with the preferred normal device structure. Our work deepens the understanding of the energetics of polymer : NFA blends and offers a basis for achieving efficient NFA properties.
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Affiliation(s)
- Fumiya Hamada
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Akinori Saeki
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
- Innovative Catalysis Science Division, Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI), Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
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7
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Chen C, Zheng S, Song H. Photon management to reduce energy loss in perovskite solar cells. Chem Soc Rev 2021; 50:7250-7329. [PMID: 33977928 DOI: 10.1039/d0cs01488e] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Despite the rapid development of perovskite solar cells (PSCs) over the past few years, the conversion of solar energy into electricity is not efficient enough or cost-competitive yet. The principal energy loss in the conversion of solar energy to electricity fundamentally originates from the non-absorption of low-energy photons ascribed to Shockley-Queisser limits and thermalization losses of high-energy photons. Enhancing the light-harvesting efficiency of the perovskite photoactive layer by developing efficient photo management strategies with functional materials and arrays remains a long-standing challenge. Here, we briefly review the historical research trials and future research trends to overcome the fundamental loss mechanisms in PSCs, including upconversion, downconversion, scattering, tandem/graded structures, texturing, anti-reflection, and luminescent solar concentrators. We will deeply emphasize the availability and analyze the importance of a fine device structure, fluorescence efficiency, material proportion, and integration position for performance improvement. The unique energy level structure arising from the 4fn inner shell configuration of the trivalent rare-earth ions gives multifarious options for efficient light-harvesting by upconversion and downconversion. Tandem or graded PSCs by combining a series of subcells with varying bandgaps seek to rectify the spectral mismatch. Plasmonic nanostructures function as a secondary light source to augment the light-trapping within the perovskite layer and carrier transporting layer, enabling enhanced carrier generation. Texturing the interior using controllable micro/nanoarrays can realize light-matter interactions. Anti-reflective coatings on the top glass cover of the PSCs bring about better transmission and glare reduction. Photon concentration through perovskite-based luminescent solar concentrators offers a path to increase efficiency at reduced cost and plays a role in building-integrated photovoltaics. Distinct from other published reviews, we here systematically and hierarchically present all of the photon management strategies in PSCs by presenting the theoretical possibilities and summarizing the experimental results, expecting to inspire future research in the field of photovoltaics, phototransistors, photoelectrochemical sensors, photocatalysis, and especially light-emitting diodes. We further assess the overall possibilities of the strategies based on ultimate efficiency prospects, material requirements, and developmental outlook.
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Affiliation(s)
- Cong Chen
- School of Material Science and Engineering, State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Dingzigu Road 1, Tianjin 300130, People's Republic of China. and State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun, 130012, People's Republic of China.
| | - Shijian Zheng
- School of Material Science and Engineering, State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Dingzigu Road 1, Tianjin 300130, People's Republic of China.
| | - Hongwei Song
- State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun, 130012, People's Republic of China.
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8
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Dynamic behavior of photogenerated charge carriers in diketopyrrolopyrrole-linked tetrabenzoporphyrin-based bulk heterojunction thin films probed with time-resolved terahertz spectroscopy. J Photochem Photobiol A Chem 2020. [DOI: 10.1016/j.jphotochem.2020.112693] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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9
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Xie X, Zhang C, Ma H. Charge transfer via deep hole in the J51/N2200 blend. J Chem Phys 2020; 153:054705. [PMID: 32770906 DOI: 10.1063/5.0013466] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
In recently developed non-fullerene acceptor (NFA) based organic solar cells (OSCs), both the donor and acceptor parts can be excited by absorbing light photons. Therefore, both the electron transfer and hole transfer channels could occur at the donor/acceptor interface for generating free charge carriers in NFA based OSCs. However, in many molecular and DNA systems, recent studies revealed that the high charge transfer (CT) efficiency cannot be reasonably explained by a CT model with only highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of donor and acceptor molecules. In this work, taking an example of a full-polymer blend consisting of benzodithiophene-alt-benzotriazole copolymers (J51) as donor and naphthalene diimide-bithiophene (N2200) as acceptor, in which the ultrafast hole transfer has been recently reported, we investigate its CT process and examine the different roles of various frontier molecular orbitals (FMOs). Through a joint study of quantum mechanics electronic structure calculation and nonadiabatic dynamics simulation, we find that the hole transfer between HOMOs of J51 and N2200 can hardly happen, but the hole transfer from HOMO of N2200 to HOMO - 1 of J51 is much more efficient. This points out the underlying importance of the deep hole channel in the CT process and indicates that including FMOs other than HOMOs and LUMOs is highly necessary to build a robust physical model for studying the CT process in molecular optoelectronic materials.
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Affiliation(s)
- Xiaoyu Xie
- School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Chunfeng Zhang
- National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Haibo Ma
- School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
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10
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Abstract
Terahertz (THz) radiation is poised to have an essential role in many imaging applications, from industrial inspections to medical diagnosis. However, commercialization is prevented by impractical and expensive THz instrumentation. Single-pixel cameras have emerged as alternatives to multi-pixel cameras due to reduced costs and superior durability. Here, by optimizing the modulation geometry and post-processing algorithms, we demonstrate the acquisition of a THz-video (32 × 32 pixels at 6 frames-per-second), shown in real-time, using a single-pixel fiber-coupled photoconductive THz detector. A laser diode with a digital micromirror device shining visible light onto silicon acts as the spatial THz modulator. We mathematically account for the temporal response of the system, reduce noise with a lock-in free carrier-wave modulation and realize quick, noise-robust image undersampling. Since our modifications do not impose intricate manufacturing, require long post-processing, nor sacrifice the time-resolving capabilities of THz-spectrometers, their greatest asset, this work has the potential to serve as a foundation for all future single-pixel THz imaging systems. Terahertz imaging is promising in many applications, but still relies on complex equipment. Here, the authors develop a simplified solution that enables terahertz real-time imaging using a single-pixel detector and rapid reconstruction methods.
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11
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Felekidis N, Melianas A, Kemerink M. The Role of Delocalization and Excess Energy in the Quantum Efficiency of Organic Solar Cells and the Validity of Optical Reciprocity Relations. J Phys Chem Lett 2020; 11:3563-3570. [PMID: 32301322 DOI: 10.1021/acs.jpclett.0c00945] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The photon energy dependence of long-range charge separation is studied for two prototypical polymer:fullerene systems. The internal quantum efficiency (IQE) of PCDTBT:PC61BM is experimentally shown to be independent of the excitation energy. In contrast, for TQ1:PC71BM the IQE is strongly energy-dependent for excitation energies close to charge transfer (CT) electroluminescence peak maximum while it becomes energy-independent at higher excitation energies. Kinetic Monte Carlo simulations reproduce the experimental IQE and reveal that the photon energy-dependence of the IQE is governed by charge delocalization. Efficient long-range separation at excitation energies corresponding to the CT electroluminescence peak maximum or lower requires an initial separation of the hole-electron pair by ∼4-5 nm, whereas delocalization is less important for charge separation at higher photon energies. Our modeling results suggest that a phenomenological reciprocity between CT electroluminescence and external quantum efficiency does not necessarily prove that commonly employed reciprocity relations between these spectra are valid from a fundamental perspective.
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Affiliation(s)
- N Felekidis
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - A Melianas
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
| | - M Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
- Centre for Advanced Materials, University of Heidelberg, 69120 Heidelberg, Germany
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12
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Banerjee S, Kang J, Zhang X, Wang LW. The effects of interstitial iodine in hybrid perovskite hot carrier cooling: A non-adiabatic molecular dynamics study. J Chem Phys 2020; 152:091102. [DOI: 10.1063/1.5132595] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Swastika Banerjee
- Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
| | - Jun Kang
- Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
| | - Xiuwen Zhang
- Shenzhen Key Laboratory of Flexible Memory Materials and Devices, College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
| | - Lin-Wang Wang
- Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
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13
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Magnanelli TJ, Engmann S, Wahlstrand JK, Stephenson JC, Richter LJ, Heilweil EJ. Polarization Dependence of Charge Conduction in Conjugated Polymer Films Investigated with Time-Resolved Terahertz Spectroscopy. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2020; 124:10.1021/acs.jpcc.9b11870. [PMID: 38680539 PMCID: PMC11047265 DOI: 10.1021/acs.jpcc.9b11870] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/01/2024]
Abstract
Room temperature Time-Domain Terahertz (TDS) and Time-Resolved Terahertz (TRTS) spectroscopic methods are employed to measure carrier mobility and charge generation efficiency in thin-film semiconductor polymers. Interrogation of the dependence on excitation and probe polarizations yields insight into the underlying material properties that guide charge transport. We apply THz polarization anisotropy probes to analyze charge conduction in preparations of the copolymer PCDTPT, consisting of alternating cyclopenta-dithiophene (donor) and thiadiazolo-pyridine (acceptor) units. Comparisons are made among films of different ordering and morphology, including aligned films prepared by blade coating, a near isotropic dropcast film, and isotropic liquid dispersion. They are further contrasted with their population dynamics ascertained through transient absorption and the traditional photoconductive polymer poly-3-hexylthiophene (P3HT). Polarization anisotropy is observed as preferential charge conduction along the backbone propagation direction of PCDTPT, with various factors disproportionately influencing directional mobility and charge pair yield. PCDTPT exhibits unexpectedly strong conductivity when isolated in toluene dispersion. Quantitative comparisons yield a better understanding of polaron/free-charge relaxation and transfer mechanisms and illustrate dynamics among photoexcited charge carriers and their motion and diffusion through different material morphologies.
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Affiliation(s)
- Timothy J. Magnanelli
- Physical, Measurement Laboratories, National Institute of Standards and Technology (NIST), Gaithersburg, MD, 20899, USA
| | - Sebastian Engmann
- Physical, Measurement Laboratories, National Institute of Standards and Technology (NIST), Gaithersburg, MD, 20899, USA
- Theiss Research, La Jolla, CA, 92036, USA
| | - Jared K. Wahlstrand
- Physical, Measurement Laboratories, National Institute of Standards and Technology (NIST), Gaithersburg, MD, 20899, USA
| | - John C. Stephenson
- Physical, Measurement Laboratories, National Institute of Standards and Technology (NIST), Gaithersburg, MD, 20899, USA
| | - Lee J. Richter
- Material, Measurement Laboratories, National Institute of Standards and Technology (NIST), Gaithersburg, MD, 20899, USA
| | - Edwin J. Heilweil
- Physical, Measurement Laboratories, National Institute of Standards and Technology (NIST), Gaithersburg, MD, 20899, USA
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14
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Melianas A, Felekidis N, Puttisong Y, Meskers SCJ, Inganäs O, Chen WM, Kemerink M. Nonequilibrium site distribution governs charge-transfer electroluminescence at disordered organic heterointerfaces. Proc Natl Acad Sci U S A 2019; 116:23416-23425. [PMID: 31690666 PMCID: PMC6876215 DOI: 10.1073/pnas.1908776116] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The interface between electron-donating (D) and electron-accepting (A) materials in organic photovoltaic (OPV) devices is commonly probed by charge-transfer (CT) electroluminescence (EL) measurements to estimate the CT energy, which critically relates to device open-circuit voltage. It is generally assumed that during CT-EL injected charges recombine at close-to-equilibrium energies in their respective density of states (DOS). Here, we explicitly quantify that CT-EL instead originates from higher-energy DOS site distributions significantly above DOS equilibrium energies. To demonstrate this, we have developed a quantitative and experimentally calibrated model for CT-EL at organic D/A heterointerfaces, which simultaneously accounts for the charge transport physics in an energetically disordered DOS and the Franck-Condon broadening. The 0-0 CT-EL transition lineshape is numerically calculated using measured energetic disorder values as input to 3-dimensional kinetic Monte Carlo simulations. We account for vibrational CT-EL overtones by selectively measuring the dominant vibrational phonon-mode energy governing CT luminescence at the D/A interface using fluorescence line-narrowing spectroscopy. Our model numerically reproduces the measured CT-EL spectra and their bias dependence and reveals the higher-lying manifold of DOS sites responsible for CT-EL. Lowest-energy CT states are situated ∼180 to 570 meV below the 0-0 CT-EL transition, enabling photogenerated carrier thermalization to these low-lying DOS sites when the OPV device is operated as a solar cell rather than as a light-emitting diode. Nonequilibrium site distribution rationalizes the experimentally observed weak current-density dependence of CT-EL and poses fundamental questions on reciprocity relations relating light emission to photovoltaic action and regarding minimal attainable photovoltaic energy conversion losses in OPV devices.
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Affiliation(s)
- Armantas Melianas
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden;
| | - Nikolaos Felekidis
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - Yuttapoom Puttisong
- Functional Electronic Materials, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - Stefan C J Meskers
- Molecular Materials and Nanosystems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
- Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
| | - Olle Inganäs
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - Weimin M Chen
- Functional Electronic Materials, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden
| | - Martijn Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183 Linköping, Sweden;
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15
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Melianas A, Kemerink M. Photogenerated Charge Transport in Organic Electronic Materials: Experiments Confirmed by Simulations. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1806004. [PMID: 30719756 DOI: 10.1002/adma.201806004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2018] [Revised: 10/29/2018] [Indexed: 06/09/2023]
Abstract
The performance of organic optoelectronic devices, such as organic photovoltaic (OPV) cells, is to a large extent dictated by their ability to transport the photogenerated charge, with relevant processes spanning a wide temporal (fs-µs) and spatial (1-100 nm) range. However, time-resolved techniques can access only a limited temporal window, and often contradict steady-state measurements. Here, commonly employed steady-state and time-resolved techniques are unified over an exceptionally wide temporal range (fs-µs) in a consistent physical picture. Experimental evidence confirmed by numerical simulations shows that, although various techniques probe different time scales, they are mutually consistent as they probe the same physical mechanisms governing charge motion in disordered media-carrier hopping and thermalization in a disorder-broadened density of states (DOS). The generality of this framework is highlighted by time-resolved experimental data obtained on polymer:fullerene, polymer:polymer, and small-molecule blends with varying morphology, including recent experiments revealing that low donor content OPV devices operate by long-range hole tunneling between non-nearest-neighbor molecules. The importance of nonequilibrium processes in organic electronic materials is reviewed, with a particular focus on experimental data and understanding charge transport physics in terms of material DOS.
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Affiliation(s)
- Armantas Melianas
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Martijn Kemerink
- Complex Materials and Devices, Department of Physics, Chemistry and Biology, Linköping University, 58183, Linköping, Sweden
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16
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Collado-Fregoso E, Pugliese SN, Wojcik M, Benduhn J, Bar-Or E, Perdigón Toro L, Hörmann U, Spoltore D, Vandewal K, Hodgkiss JM, Neher D. Energy-Gap Law for Photocurrent Generation in Fullerene-Based Organic Solar Cells: The Case of Low-Donor-Content Blends. J Am Chem Soc 2019; 141:2329-2341. [PMID: 30620190 DOI: 10.1021/jacs.8b09820] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The involvement of charge-transfer (CT) states in the photogeneration and recombination of charge carriers has been an important focus of study within the organic photovoltaic community. In this work, we investigate the molecular factors determining the mechanism of photocurrent generation in low-donor-content organic solar cells, where the active layer is composed of vacuum-deposited C60 and small amounts of organic donor molecules. We find a pronounced decline of all photovoltaic parameters with decreasing CT state energy. Using a combination of steady-state photocurrent measurements and time-delayed collection field experiments, we demonstrate that the power conversion efficiency, and more specifically, the fill factor of these devices, is mainly determined by the bias dependence of photocurrent generation. By combining these findings with the results from ultrafast transient absorption spectroscopy, we show that blends with small CT energies perform poorly because of an increased nonradiative CT state decay rate and that this decay obeys an energy-gap law. Our work challenges the common view that a large energy offset at the heterojunction and/or the presence of fullerene clusters guarantee efficient CT dissociation and rather indicates that charge generation benefits from high CT state energies through a slower decay to the ground state.
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Affiliation(s)
- Elisa Collado-Fregoso
- Department of Physics and Astronomy , University of Potsdam , Karl-Liebknecht-Straße 24-25 , 14476 Potsdam-Golm , Germany
| | - Silvina N Pugliese
- School of Chemical and Physical Sciences , Victoria University of Wellington , Wellington 6040 , New Zealand.,The MacDiarmid Institute for Advanced Materials and Nanotechnology , Wellington 6040 , New Zealand
| | - Mariusz Wojcik
- Institute of Applied Radiation Chemistry , Lodz University of Technology , Wroblewskiego 15 , 93590 Lodz , Poland
| | - Johannes Benduhn
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , Nöthnitzer Straße 61 , 01187 Dresden , Germany
| | - Eyal Bar-Or
- Department of Physics and Astronomy , University of Potsdam , Karl-Liebknecht-Straße 24-25 , 14476 Potsdam-Golm , Germany
| | - Lorena Perdigón Toro
- Department of Physics and Astronomy , University of Potsdam , Karl-Liebknecht-Straße 24-25 , 14476 Potsdam-Golm , Germany
| | - Ulrich Hörmann
- Department of Physics and Astronomy , University of Potsdam , Karl-Liebknecht-Straße 24-25 , 14476 Potsdam-Golm , Germany
| | - Donato Spoltore
- Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics , Technische Universität Dresden , Nöthnitzer Straße 61 , 01187 Dresden , Germany
| | - Koen Vandewal
- Institute for Materials Research (IMO-IMOMEC) , Hasselt University , Wetenschapspark 1 , 3590 Diepenbeek , Belgium
| | - Justin M Hodgkiss
- School of Chemical and Physical Sciences , Victoria University of Wellington , Wellington 6040 , New Zealand.,The MacDiarmid Institute for Advanced Materials and Nanotechnology , Wellington 6040 , New Zealand
| | - Dieter Neher
- Department of Physics and Astronomy , University of Potsdam , Karl-Liebknecht-Straße 24-25 , 14476 Potsdam-Golm , Germany
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17
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Kurpiers J, Ferron T, Roland S, Jakoby M, Thiede T, Jaiser F, Albrecht S, Janietz S, Collins BA, Howard IA, Neher D. Probing the pathways of free charge generation in organic bulk heterojunction solar cells. Nat Commun 2018; 9:2038. [PMID: 29795114 PMCID: PMC5966440 DOI: 10.1038/s41467-018-04386-3] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 04/24/2018] [Indexed: 11/30/2022] Open
Abstract
The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges. Contradictory models are being debated on the dominant pathways of charge generation in organic solar cells. Here Kurpiers et al. determine the activation energy for this fundamental process and reveal that the main channel is via thermalized charge transfer states instead of hot exciton dissociation.
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Affiliation(s)
- Jona Kurpiers
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Thomas Ferron
- Department of Physics and Astronomy, Washington State University, 100 Dairy Road, Pullman, WA, 99164, USA
| | - Steffen Roland
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Marius Jakoby
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology (IMT), Hermann-von-Helmholtz Platz-1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Tobias Thiede
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Frank Jaiser
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany
| | - Steve Albrecht
- Helmholtz-Zentrum Berlin für Materialien und Energie, Nachwuchsgruppe Perowskit Tandemsolarzellen, Kekuléstraße 5, 12489, Berlin, Germany
| | - Silvia Janietz
- Fraunhofer IAP, Polymere und Elektronik, Geiselbergstraße 69, 14476, Potsdam-Golm, Germany
| | - Brian A Collins
- Department of Physics and Astronomy, Washington State University, 100 Dairy Road, Pullman, WA, 99164, USA
| | - Ian A Howard
- Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology (IMT), Hermann-von-Helmholtz Platz-1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Dieter Neher
- Institute of Physics and Astronomy, Soft Matter Physics, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
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18
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Chochos CL, Singh R, Gregoriou VG, Kim M, Katsouras A, Serpetzoglou E, Konidakis I, Stratakis E, Cho K, Avgeropoulos A. Enhancement of the Power-Conversion Efficiency of Organic Solar Cells via Unveiling an Appropriate Rational Design Strategy in Indacenodithiophene- alt-quinoxaline π-Conjugated Polymers. ACS APPLIED MATERIALS & INTERFACES 2018; 10:10236-10245. [PMID: 29508996 DOI: 10.1021/acsami.7b18381] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We report on the photovoltaic parameters, photophysical properties, optoelectronic properties, self-assembly, and morphology variations in a series of high-performance donor-acceptor (D-A) π-conjugated polymers based on indacenodithiophene and quinoxaline moieties as a function of the number-average molecular weight ([Formula: see text]), the nature of aryl substituents, and the enlargement of the polymer backbone. One of the most important outcome is that from the three optimization approaches followed to tune the chemical structure toward enhanced photovoltaic performance in bulk heterojunction solar cell devices with the fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester as the electron acceptor, the choice of the aryl substituent is the most efficient rational design strategy. Incorporation of thienyl rings as substituents versus phenyl rings accelerates the electron-hole extraction process to the respective electrode, despite the slightly lower recombination lifetime and, thus, improves the electrical performance of the device. Single-junction solar cells based on ThIDT-TQxT feature a maximum power-conversion efficiency of 7.26%. This study provides significant insights toward understanding of the structure-properties-performance relationship for D-A π-conjugated polymers in solid state, which provide helpful inputs for the design of next-generation polymeric semiconductors for organic solar cells with enhanced performance.
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Affiliation(s)
- Christos L Chochos
- Department of Materials Science Engineering , University of Ioannina , Ioannina 45110 , Greece
- Advent Technologies SA , Patras Science Park, Stadiou Street , Platani-Rio, 26504 Patras , Greece
| | - Ranbir Singh
- Department of Chemical Engineering , Pohang University of Science and Technology , Pohang 790-784 , Korea
| | - Vasilis G Gregoriou
- Advent Technologies SA , Patras Science Park, Stadiou Street , Platani-Rio, 26504 Patras , Greece
- National Hellenic Research Foundation (NHRF) , 48 Vassileos Constantinou Avenue , Athens 11635 , Greece
| | - Min Kim
- Department of Chemical Engineering , Pohang University of Science and Technology , Pohang 790-784 , Korea
| | - Athanasios Katsouras
- Department of Materials Science Engineering , University of Ioannina , Ioannina 45110 , Greece
| | - Efthymis Serpetzoglou
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas , P.O. Box 1527, Heraklion 71110 , Crete , Greece
| | - Ioannis Konidakis
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas , P.O. Box 1527, Heraklion 71110 , Crete , Greece
| | - Emmanuel Stratakis
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas , P.O. Box 1527, Heraklion 71110 , Crete , Greece
| | - Kilwon Cho
- Department of Chemical Engineering , Pohang University of Science and Technology , Pohang 790-784 , Korea
| | - Apostolos Avgeropoulos
- Department of Materials Science Engineering , University of Ioannina , Ioannina 45110 , Greece
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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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Petti MK, Lomont JP, Maj M, Zanni MT. Two-Dimensional Spectroscopy Is Being Used to Address Core Scientific Questions in Biology and Materials Science. J Phys Chem B 2018; 122:1771-1780. [PMID: 29346730 DOI: 10.1021/acs.jpcb.7b11370] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two-dimensional spectroscopy is a powerful tool for extracting structural and dynamic information from a wide range of chemical systems. We provide a brief overview of the ways in which two-dimensional visible and infrared spectroscopies are being applied to elucidate fundamental details of important processes in biological and materials science. The topics covered include amyloid proteins, photosynthetic complexes, ion channels, photovoltaics, batteries, as well as a variety of promising new methods in two-dimensional spectroscopy.
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Affiliation(s)
- Megan K Petti
- Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
| | - Justin P Lomont
- Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
| | - Michał Maj
- Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
| | - Martin T Zanni
- Department of Chemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States
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21
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Ohta K, Tokonami S, Takahashi K, Tamura Y, Yamada H, Tominaga K. Probing Charge Carrier Dynamics in Porphyrin-Based Organic Semiconductor Thin Films by Time-Resolved THz Spectroscopy. J Phys Chem B 2017; 121:10157-10165. [DOI: 10.1021/acs.jpcb.7b07025] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Kaoru Ohta
- Molecular
Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
- Graduate
School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Shunrou Tokonami
- Graduate
School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
| | - Kotaro Takahashi
- Graduate
School of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Yuto Tamura
- Graduate
School of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Hiroko Yamada
- Graduate
School of Materials Science, Nara Institute of Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Keisuke Tominaga
- Molecular
Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
- Graduate
School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501, Japan
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22
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Ponseca CS, Chábera P, Uhlig J, Persson P, Sundström V. Ultrafast Electron Dynamics in Solar Energy Conversion. Chem Rev 2017; 117:10940-11024. [DOI: 10.1021/acs.chemrev.6b00807] [Citation(s) in RCA: 211] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Carlito S. Ponseca
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Pavel Chábera
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Jens Uhlig
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Petter Persson
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
| | - Villy Sundström
- Division
of Chemical Physics, Chemical Center, and ‡Theoretical Chemistry Division,
Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden
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23
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Dunkelberger A, Compton R, DeSario PA, Weidinger D, Spann BT, Pala IR, Chervin CN, Rolison DR, Bussmann K, Cunningham P, Melinger JS, Alberding BG, Heilweil EJ, Owrutsky JC. Transient Optical and Terahertz Spectroscopy of Nanoscale Films of RuO 2. PLASMONICS (NORWELL, MASS.) 2017; 12:743-750. [PMID: 28503102 PMCID: PMC5424710 DOI: 10.1007/s11468-016-0321-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 06/29/2016] [Indexed: 05/25/2023]
Abstract
Solution-deposited nanoscale films of RuO2 ("nanoskins") are effective transparent conductors once calcined to 200 °C. Upon heating the nanoskins to higher temperature the nanoskins show increased transmission at 550 nm. Electronic microscopy and X-ray diffraction show that the changes in the optical spectrum are accompanied by the formation of rutile RuO2 nanoparticles. The mechanism for the spectral evolution is clearly observed with ultrafast optical measurements. Following excitation at 400 nm, nanoskins calcined at higher temperatures show increased transmission above 650 nm, consistent with the photobleaching of a surface-plasmon resonance (SPR) band. Calculations based on the optical constants of RuO2 substantiate the presence of SPR absorption. Sheet resistance and transient terahertz photoconductivity measurements establish that the nanoskins electrically de-wire into separated particles. The plasmonic behavior of the nanoskins has implications their use in a range of optical and electrochemical applications.
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Affiliation(s)
- Adam Dunkelberger
- Naval Research Laboratory/National Research Council Postdoctoral Fellow
| | - Ryan Compton
- Naval Research Laboratory/National Research Council Postdoctoral Fellow
| | - Paul A. DeSario
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Daniel Weidinger
- Schaffer Corp. 3811 North Fairfax Drive, Suite 400, Arlington, VA, USA
| | - Bryan T. Spann
- Naval Research Laboratory/National Research Council Postdoctoral Fellow
| | - Irina R. Pala
- Naval Research Laboratory/National Research Council Postdoctoral Fellow
| | - Christopher N. Chervin
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Debra R. Rolison
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Konrad Bussmann
- Materials Science and Technology Division, Code 6300, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Paul Cunningham
- Electronic Science and Technology Division, Code 6800, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Joseph S. Melinger
- Electronic Science and Technology Division, Code 6800, U.S. Naval Research Laboratory, Washington, DC 20375, USA
| | - Brian G. Alberding
- National Institute of Standards & Technology/National Research Council Postdoctoral Associate
| | - Edwin J. Heilweil
- National Institute of Standards &Technology, Gaithersburg, MD 20899, USA
| | - Jeffrey C. Owrutsky
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, DC 20375, USA
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24
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Alberding BG, DeSario PA, So CR, Dunkelberger AD, Rolison DR, Owrutsky JC, Heilweil EJ. Static and Time-Resolved Terahertz Measurements of Photoconductivity in Solution-Deposited Ruthenium Dioxide Nanofilms. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2017; 121:4037-4044. [PMID: 28890744 PMCID: PMC5590661 DOI: 10.1021/acs.jpcc.6b12382] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Thin-film ruthenium dioxide (RuO2) is a promising alternative material as a conductive electrode in electronic applications because its rutile crystalline form is metallic and highly conductive. Herein, a solution-deposition multi-layer technique is employed to fabricate ca. 70 ± 20 nm thick films (nanoskins) and terahertz spectroscopy is used to determine their photoconductive properties. Upon calcining at temperatures ranging from 373 K to 773 K, nanoskins undergo a transformation from insulating (localized charge transport) behavior to metallic behavior. Terahertz time-domain spectroscopy (THz-TDS) indicates that nanoskins attain maximum static conductivity when calcined at 673 K (σ = 1030 ± 330 S·cm-1). Picosecond time-resolved Terahertz spectroscopy (TRTS) using 400 nm and 800 nm excitation reveals a transition to metallic behavior when calcined at 523 K. For calcine temperatures less than 523 K, the conductivity increases following photoexcitation (ΔE < 0) while higher calcine temperatures yield films composed of crystalline, rutile RuO2 and the conductivity decreases (ΔE > 0) following photoexcitation.
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Affiliation(s)
- Brian G. Alberding
- Radiation Physics Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Paul A. DeSario
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, D.C., 20375 USA
| | - Christopher R. So
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, D.C., 20375 USA
| | | | - Debra R. Rolison
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, D.C., 20375 USA
| | - Jeffrey C. Owrutsky
- Chemistry Division, Code 6100, U.S. Naval Research Laboratory, Washington, D.C., 20375 USA
| | - Edwin J. Heilweil
- Radiation Physics Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
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25
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Direct observation of photocarrier electron dynamics in C 60 films on graphite by time-resolved two-photon photoemission. Sci Rep 2016; 6:35853. [PMID: 27775005 PMCID: PMC5075791 DOI: 10.1038/srep35853] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 10/06/2016] [Indexed: 12/27/2022] Open
Abstract
Time-resolved two-photon photoemission (TR-2PPE) spectroscopy is employed to probe the electronic states of a C60 fullerene film formed on highly oriented pyrolytic graphite (HOPG), acting as a model two-dimensional (2D) material for multi-layered graphene. Owing to the in-plane sp2-hybridized nature of the HOPG, the TR-2PPE spectra reveal the energetics and dynamics of photocarriers in the C60 film: after hot excitons are nascently formed in C60 via intramolecular excitation by a pump photon, they dissociate into photocarriers of free electrons and the corresponding holes, and the electrons are subsequently detected by a probe photon as photoelectrons. The decay rate of photocarriers from the C60 film into the HOPG is evaluated to be 1.31 × 1012 s−1, suggesting a weak van der Waals interaction at the interface, where the photocarriers tentatively occupy the lowest unoccupied molecular orbital (LUMO) of C60. The photocarrier electron dynamics following the hot exciton dissociation in the organic thin films has not been realized for any metallic substrates exhibiting strong interactions with the overlayer. Furthermore, the thickness dependence of the electron lifetime in the LUMO reveals that the electron hopping rate in C60 layers is 3.3 ± 1.2 × 1013 s−1.
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26
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Alberding BG, Biacchi AJ, Walker ARH, Heilweil EJ. Charge Carrier Dynamics and Mobility Determined by Time-Resolved Terahertz Spectroscopy on Films of Nano-to-Micrometer-Sized Colloidal Tin(II) Monosulfide. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2016; 120:15395-15406. [PMID: 27766125 PMCID: PMC5066166 DOI: 10.1021/acs.jpcc.6b01684] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Tin(II) monosulfide (SnS) is a semiconductor material with an intermediate band gap, high absorption coefficient in the visible range, and earth abundant, non-toxic constituent elements. For these reasons, SnS has generated much interest for incorporation into optoelectronic devices, but little is known concerning the charge carrier dynamics, especially as measured by optical techniques. Here, as opposed to prior studies of vapor deposited films, phase-pure colloidal SnS was synthesized by solution chemistry in three size regimes, ranging from nanometer- to micron-scale (SnS small nanoparticles, SnS medium 2D nanosheets, and SnS large 2D μm-sheets), and evaluated by time-resolved terahertz spectroscopy (TRTS); an optical, non-contact probe of the photoconductivity. Dropcast films of the SnS colloids were studied by TRTS and compared to both thermally annealed films and dispersed suspensions of the same colloids. TRTS results revealed that the micron-scale SnS crystals and all of the annealed films undergo decay mechanisms during the first 200 ps following photoexcitation at 800 nm assigned to hot carrier cooling and carrier trapping. The charge carrier mobility of both the dropcast and annealed samples depends strongly on the size of the constituent colloids. The mobility of the SnS colloidal films, following the completion of the initial decays, ranged from 0.14 cm2/V·s for the smallest SnS crystals to 20.3 cm2/V·s for the largest. Annealing the colloidal films resulted in a ~ 20 % improvement in mobility for the large SnS 2D μm-sheets and a ~ 5-fold increase for the small nanoparticles and medium nanosheets.
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Affiliation(s)
- Brian G. Alberding
- Radiation Physics Division, National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland, 20899, United States
| | - Adam J. Biacchi
- Engineering Physics Division, National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland, 20899, United States
| | - Angela R. Hight Walker
- Engineering Physics Division, National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland, 20899, United States
| | - Edwin J. Heilweil
- Radiation Physics Division, National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, Maryland, 20899, United States
- (301-975-2370)
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27
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Pranculis V, Ruseckas A, Vithanage D, Hedley GJ, Samuel IDW, Gulbinas V. Influence of Blend Ratio and Processing Additive on Free Carrier Yield and Mobility in PTB7:PC 71BM Photovoltaic Solar Cells. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2016; 120:9588-9594. [PMID: 27293495 PMCID: PMC4897731 DOI: 10.1021/acs.jpcc.6b01548] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 04/21/2016] [Indexed: 06/06/2023]
Abstract
Charge separation and extraction dynamics were investigated in high-performance bulk heterojunction solar cells made from the polymer PTB7 and the soluble fullerene PC71BM on a broad time scale from subpicosecond to microseconds using ultrafast optical probing of carrier drift and the integral-mode photocurrent measurements. We show that the short circuit current is determined by the separation of charge pairs into free carriers, which is strongly influenced by blend composition. This separation is found to be efficient in fullerene-rich blends where a high electron mobility of >0.1 cm2 V-1 s-1 is observed in the first 10 ps after excitation. Morphology optimization using the solvent additive 1,8-diiodooctane (DIO) doubles the charge pair separation efficiency and the short-circuit current. Carrier extraction at low internal electric field is slightly faster from the cells prepared with DIO, which can reduce recombination losses and enhance a fill factor.
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Affiliation(s)
- Vytenis Pranculis
- Center
for Physical Sciences and Technology, Savanoriu Ave 231, 02300 Vilnius, Lithuania
| | - Arvydas Ruseckas
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Dimali
A. Vithanage
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Gordon J. Hedley
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Ifor D. W. Samuel
- Organic
Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - Vidmantas Gulbinas
- Center
for Physical Sciences and Technology, Savanoriu Ave 231, 02300 Vilnius, Lithuania
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Cunningham PD, Lane PA, Melinger JS, Esenturk O, Heilweil EJ. Probing Charge Transfer and Hot Carrier Dynamics in Organic Solar Cells with Terahertz Spectroscopy. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2016. [PMID: 28649166 DOI: 10.1117/12.2228379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Time-resolved terahertz spectroscopy (TRTS) was used to explore charge generation, transfer, and the role of hot carriers in organic solar cell materials. Two model molecular photovoltaic systems were investigated: with zinc phthalocyanine (ZnPc) or alpha-sexathiophene (α-6T) as the electron donors and buckminsterfullerene (C60) as the electron acceptor. TRTS provides charge carrier conductivity dynamics comprised of changes in both population and mobility. By using time-resolved optical spectroscopy in conjunction with TRTS, these two contributions can be disentangled. The sub-picosecond photo-induced conductivity decay dynamics of C60 were revealed to be caused by auto-ionization: the intrinsic process by which charge is generated in molecular solids. In donor-acceptor blends, the long-lived photo-induced conductivity is used for weight fraction optimization of the constituents. In nanoscale multilayer films, the photo-induced conductivity identifies optimal layer thicknesses. In films of ZnPc/C60, electron transfer from ZnPc yields hot charges that localize and become less mobile as they thermalize. Excitation of high-lying Franck Condon states in C60 followed by hole-transfer to ZnPc similarly produces hot charge carriers that self-localize; charge transfer clearly precedes carrier cooling. This picture is contrasted to charge transfer in α-6T/C60, where hole transfer takes place from a thermalized state and produces equilibrium carriers that do not show characteristic signs of cooling and self-localization. These results illustrate the value of terahertz spectroscopic methods for probing charge transfer reactions.
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Affiliation(s)
| | - Paul A Lane
- U.S. Naval Research Laboratory, Washington, DC 20375, United States
| | | | - Okan Esenturk
- Chemistry Department, Middle East Technical University, Ankara, Turkey
| | - Edwin J Heilweil
- National Institute of Standards and Technology, Gaithersburg, MD 20899, United States
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