I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[30708, 30349]
Open Access
Abstract: We have studied the charge transport physics of high-quality conducting coordination nanosheets films based on the benchmark material copper benzenehexathiol (CuBHT) by measuring multiple thermoelectric and magnetotransport coefficients on the same film. The films exhibit a metallic temperature dependence of the conductivity over a wide temperature range, but below 15 kelvin charge transport becomes dominated by weak localization and electron-electron interactions. Temperature-dependent Hall, Seebeck, and Nernst measurements consistently indicate the existence of ambipolar transport characteristics in CuBHT. A two-band analysis has been used to extract transport parameters for electron and hole carriers as a function of temperature. The results show that contributions from electron and hole conduction in CuBHT are of comparable magnitude, revealing the complexity of charge transport and allowing one to identify strategies for enhancing the thermoelectric transport coefficients of such conducting coordination nanosheets.
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Apr 2025
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I07-Surface & interface diffraction
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Dionisius H. L.
Tjhe
,
Xinglong
Ren
,
Ian
Jacobs
,
Gabriele
D'Avino
,
Tarig B. E.
Mustafa
,
Thomas G.
Marsh
,
Lu
Zhang
,
Yao
Fu
,
Ahmed E.
Mansour
,
Andreas
Opitz
,
Yuxuan
Huang
,
Wenjin
Zhu
,
Ahmet Hamdi
Unal
,
Sebastiaan
Hoek
,
Vincent
Lemaur
,
Claudio
Quarti
,
Qiao
He
,
Jin-Kyun
Lee
,
Iain
Mcculloch
,
Martin
Heeney
,
Norbert
Koch
,
Clare P.
Grey
,
David
Beljonne
,
Simone
Fratini
,
Henning
Sirringhaus
Diamond Proposal Number(s):
[30708, 30349]
Open Access
Abstract: Conducting polymers are mixed ionic–electronic conductors that are emerging candidates for neuromorphic computing, bioelectronics and thermoelectrics. However, fundamental aspects of their many-body correlated electron–ion transport physics remain poorly understood. Here we show that in p-type organic electrochemical transistors it is possible to remove all of the electrons from the valence band and even access deeper bands without degradation. By adding a second, field-effect gate electrode, additional electrons or holes can be injected at set doping states. Under conditions where the counterions are unable to equilibrate in response to field-induced changes in the electronic carrier density, we observe surprising, non-equilibrium transport signatures that provide unique insights into the interaction-driven formation of a frozen, soft Coulomb gap in the density of states. Our work identifies new strategies for substantially enhancing the transport properties of conducting polymers by exploiting non-equilibrium states in the coupled system of electronic charges and counterions.
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Jul 2024
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E02-JEM ARM 300CF
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Alexander J.
Sneyd
,
Tomoya
Fukui
,
David
Paleček
,
Suryoday
Prodhan
,
Isabella
Wagner
,
Yifan
Zhang
,
Jooyoung
Sung
,
Sean M.
Collins
,
Thomas J. A.
Slater
,
Zahra
Andaji-Garmaroudi
,
Liam R.
Macfarlane
,
J. Diego
Garcia-Hernandez
,
Linjun
Wang
,
George R.
Whittell
,
Justin M.
Hodgkiss
,
Kai
Chen
,
David
Beljonne
,
Ian
Manners
,
Richard H.
Friend
,
Akshay
Rao
Diamond Proposal Number(s):
[25140]
Open Access
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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Aug 2021
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I07-Surface & interface diffraction
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Alberto
Privitera
,
Ross
Warren
,
Giacomo
Londi
,
Pascal
Kaienburg
,
Junjie
Liu
,
Andreas
Sperlich
,
Andreas E.
Lauritzen
,
Oliver
Thimm
,
Arzhang
Ardavan
,
David
Beljonne
,
Moritz
Riede
Diamond Proposal Number(s):
[20426]
Open Access
Abstract: We use the electron spin as a probe to gain insight into the mechanism of molecular doping in a p-doped zinc phthalocyanine host across a broad range of temperatures (80–280 K) and doping concentrations (0–5 wt% of F6-TCNNQ). Electron paramagnetic resonance (EPR) spectroscopy discloses the presence of two main paramagnetic species distinguished by two different g-tensors, which are assigned based on density functional theory calculations to the formation of a positive polaron on the host and a radical anion on the dopant. Close inspection of the EPR spectra shows that radical anions on the dopants couple in an antiferromagnetic manner at device-relevant doping concentrations, thereby suggesting the presence of dopant clustering, and that positive polarons on the molecular host move by polaron hopping with an activation energy of 5 meV. This activation energy is substantially smaller than that inferred from electrical conductivity measurements (∼233 meV), as the latter also includes a (major) contribution from charge-transfer state dissociation. It emerges from this study that probing the electron spin can provide rich information on the nature and dynamics of charge carriers generated upon doping molecular semiconductors, which could serve as a basis for the design of the next generation of dopant and host materials.
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Feb 2021
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I07-Surface & interface diffraction
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Edward P.
Booker
,
Tudor H.
Thomas
,
Claudio
Quarti
,
Michael R.
Stanton
,
Cameron D.
Dashwood
,
Alexander J.
Gillett
,
Johannes M.
Richter
,
Andrew J.
Pearson
,
Nathaniel J. L. K.
Davis
,
Henning
Sirringhaus
,
Michael B.
Price
,
Neil C.
Greenham
,
David
Beljonne
,
Sian E.
Dutton
,
Felix
Deschler
Diamond Proposal Number(s):
[14886]
Open Access
Abstract: We investigate the origin of the broadband visible emission in layered hybrid lead-halide perovskites and its connection with structural and photophysical properties. We study <001> oriented thin films of hexylammonium (HA) lead iodide, (C6H16N)2PbI4, and dodecylammonium (DA) lead iodide, (C12H28N)2PbI4 by combining first-principles simulations with time-resolved photoluminescence, steady-state absorption and X-ray diffraction measurements on cooling from 300 K to 4 K. Ultrafast transient absorption and photoluminescence measurements are used to track the formation and recombination of emissive states. In addition to the excitonic photoluminescence near the absorption edge, we find a red-shifted, broadband (full-width at half maximum of about 0.4 eV), emission band below 200 K, similar to emission from <110> oriented bromide 2D perovskites at room temperature. The lifetime of this sub-bandgap emission exceeds that of the excitonic transition by orders of magnitude. We use X-ray diffraction measurements to study the changes in crystal lattice with temperature. We report changes in the octahedral tilt and lattice spacing in both materials, together with a phase change around 200 K in DA2PbI4. DFT simulations of the HA2PbI4 crystal structure indicate that the low-energy emission is due to interstitial iodide and related Frenkel defects. Our results demonstrate that white-light emission is not limited to <110> oriented bromide 2D perovskites but a general property of this class of system and highlight the importance of defect control for the formation of low-energy emissive sites, which can provide a pathway to design tailored white-light emitters.
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Nov 2017
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I19-Small Molecule Single Crystal Diffraction
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Georgios
Charalambidis
,
Evangelos
Georgilis
,
Manas K.
Panda
,
Christopher E.
Anson
,
Annie K.
Powell
,
Stephen
Doyle
,
David
Moss
,
Tobias
Jochum
,
Peter N.
Horton
,
Simon J.
Coles
,
Mathieu
Linares
,
David
Beljonne
,
Jean-Valère
Naubron
,
Jonas
Conradt
,
Heinz
Kalt
,
Anna
Mitraki
,
Athanassios G.
Coutsolelos
,
Teodor Silviu
Balaban
Diamond Proposal Number(s):
[8521]
Open Access
Abstract: Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. Here we describe a simple and robust FLFL-dipeptide construct to which a meso-tetraphenylporphyrin has been appended and which self-assembles to fibrils, platelets or nanospheres depending on the solvent composition. The fibrils, functioning as quenched antennas, give intense excitonic couplets in the electronic circular dichroism spectra which are mirror imaged if the unnatural FDFD-analogue is used. By slightly increasing the solvent polarity, these light-harvesting fibres disassemble to spherical structures with silent electronic circular dichroism spectra but which fluoresce. Upon further dilution with the nonpolar solvent, the intense Cotton effects are recovered, thus proving a reversible switching. A single crystal X-ray structure shows a head-to-head arrangement of porphyrins that explains both their excitonic coupling and quenched fluorescence.
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Sep 2016
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I22-Small angle scattering & Diffraction
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Giuseppe
Sforazzini
,
Axel
Kahnt
,
Michael
Wykes
,
Johannes
Sprafke
,
Sergio
Brovelli
,
Damien
Montarnal
,
Francesco
Meinardi
,
Franco
Cacialli
,
David
Beljonne
,
Bo
Albinsson
,
Harry L.
Anderson
Abstract: Conjugated polyrotaxanes jacketed with hole-transport groups have been synthesized from water-soluble polyrotaxanes consisting of a polyfluorene-alt-biphenylene (PFBP) conjugated polymer threaded through beta-cyclodextrin macrocycles. The hydroxyl groups of the oligosaccharides were efficiently functionalized with triphenylamine (TPA) so that every polyrotaxane molecule carries a coat of about 200 TPA units, forming a supramolecular coaxial structure. This architecture was characterized using a range of techniques, including small-angle X-ray scattering. Absorption of light by the TPA units results in excitation energy transfer (EET) and photoinduced electron transfer (ET) to the inner conjugated polymer core. These energy- and charge-transfer processes were explored by steady-state and time-resolved fluorescence spectroscopy, femtosecond transient absorption spectroscopy, and molecular modeling. The time-resolved measurements yielded insights into the heterogeneity of the TPA coat: those TPA units which are close to the central polymer core tend to undergo ET, whereas those on the outer surface of the polyrotaxane, far from the core, undergo EET. Sections of the backbone that are excited indirectly via EET tend to be more remote from the TPA units and thus are less susceptible to electron-transfer quenching. The rate of EET from the TPA units to the PFBP core was effectively modeled by taking account of the heterogeneity in the TPA-PFBP distance, using a distributed monopole approach. This work represents a new strategy for building and studying well-defined arrays of >100 covalently linked chromophores.
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Feb 2014
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I22-Small angle scattering & Diffraction
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Kerr
Johnson
,
Ya-Shih
Huang
,
Sven
Huettner
,
Michael
Sommer
,
Martin
Brinkmann
,
Rhiannon Clare
Mulherin
,
Dorota
Niedzialek
,
David
Beljonne
,
Jenny
Clark
,
Wilhelm T. S.
Huck
,
Richard H.
Friend
Abstract: We report the electronic properties of the conjugated coupling between a donor polymer and an acceptor segment serving as a model for the coupling in conjugated donor–acceptor block copolymers. These structures allow the study of possible intrachain photoinduced charge separation, in contrast to the interchain separation achieved in conventional donor–acceptor blends. Depending on the nature of the conjugated linkage, we observe varying degrees of modification of the excited states, including the formation of intrachain charge transfer excitons. The polymers comprise a block (typically 18 repeat units) of P3HT, poly(3-hexyl thiophene), coupled to a single unit of F8-TBT (where F8 is dioctylfluorene, and TBT is thiophene-benzothiadiazole-thiophene). When the P3HT chain is linked to the TBT unit, we observe formation of a localized charge transfer state, with red-shifted absorption and emission. Independent of the excitation energy, this state is formed very rapidly (<40 fs) and efficiently. Because there is only a single TBT unit present, there is little scope for long-range charge separation and it is relatively short-lived, <1 ns. In contrast, when the P3HT chain and TBT unit are separated by the wider bandgap F8 unit, there is little indication for modification of either ground or excited electronic states, and longer-lived charge separated states are observed.
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Mar 2013
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I19-Small Molecule Single Crystal Diffraction
I22-Small angle scattering & Diffraction
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Johannes
Sprafke
,
Dmitry
Kondratiuk
,
Michael
Wykes
,
Amber
Thompson
,
Marcus
Hoffman
,
Rokas
Drevinskas
,
Wei-Hsin
Chen
,
Chaw
Keong Yong
,
Joakim
Kärnbratt
,
Joseph
Bullock
,
Marc
Malfois
,
Michael
Wasielewski
,
Bo
Albinsson
,
Laura
Herz
,
Donatas
Zigmantas
,
David
Beljonne
,
Harry
Anderson
Abstract: Linear π-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of π-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a π-conjugated butadiyne-linked cyclic porphyrin hexamer directly from the monomer. Small-angle X-ray scattering data show that this nanoring is shape-persistent in solution, even without its template, whereas the linear porphyrin hexamer is relatively flexible. The crystal structure of the nanoring–template complex shows that most of the strain is localized in the acetylenes; the porphyrin units are slightly curved, but the zinc coordination sphere is undistorted. The electrochemistry, absorption, and fluorescence spectra indicate that the HOMO–LUMO gap of the nanoring is less than that of the linear hexamer and less than that of the corresponding polymer. The nanoring exhibits six one-electron reductions and six one-electron oxidations, most of which are well resolved. Ultrafast fluorescence anisotropy measurements show that absorption of light generates an excited state that is delocalized over the whole π-system within a time of less than 0.5 ps. The fluorescence spectrum is amazingly structured and red-shifted. A similar, but less dramatic, red-shift has been reported in the fluorescence spectra of cycloparaphenylenes and was attributed to a high exciton binding energy; however the exciton binding energy of the porphyrin nanoring is similar to those of linear oligomers. Quantum-chemical excited state calculations show that the fluorescence spectrum of the nanoring can be fully explained in terms of vibronic Herzberg–Teller (HT) intensity borrowing.
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Sep 2011
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