Imperial College London

ProfessorAronWalsh

Faculty of EngineeringDepartment of Materials

Chair in Materials Design
 
 
 
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Contact

 

+44 (0)20 7594 1178a.walsh Website

 
 
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Location

 

2.10Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

404 results found

Yang H, Savory CN, Morgan BJ, Scanlon DO, Skelton JM, Walsh Aet al., 2020, Chemical Trends in the Lattice Thermal Conductivity of Li(Ni, Mn, Co)O2 (NMC) Battery Cathodes, Chemistry of Materials, Vol: 32, Pages: 7542-7550, ISSN: 0897-4756

Journal article

Moss B, Le H, Corby S, Morita K, Selim S, Sotelo-Vazquez C, Chen Y, Borthwick A, Wilson A, Blackman C, Durrant JR, Walsh A, Kafizas Aet al., 2020, Anisotropic electron transport limits performance of Bi2WO6 photoanodes, The Journal of Physical Chemistry C, Vol: 124, Pages: 18859-18867, ISSN: 1932-7447

Bi2WO6 is one of the simplest members of the versatile Aurivillius oxide family of materials. As an intriguing model system for Aurivillius oxides, BiVO4 exhibits low water oxidation onset potentials (∼0.5–0.6 VRHE) for driven solar water oxidation. Despite this, Bi2WO6 also produces low photocurrents in comparison to other metal oxides. Due to a lack of in situ studies, the reasons for such poor performance are not understood. In this study, Bi2WO6 photoanodes are synthesized by aerosol-assisted chemical vapor deposition. The charge carrier dynamics of Bi2WO6 are studied in situ under water oxidation conditions, and the rate of both bulk recombination and water oxidation is found to be comparable to other metal oxide photoanodes. However, the rate of electron extraction is at least 10 times slower than the slowest kinetics previously reported in an oxide photoanode. First-principles analysis indicates that the slow electron extraction kinetics are linked to a strong anisotropy in the conduction band. Preferred or epitaxial growth along the conductive axes is a strategy to overcome slow electron transport and low photocurrent densities in layered materials such as Bi2WO6.

Journal article

Walsh A, Park JS, 2020, The Holey Grail of Transparent Electronics, Matter, Vol: 3, Pages: 604-606, ISSN: 2590-2393

© 2020 Elsevier Inc. For decades, researchers have attempted to discover transparent conductors that transport holes. A robust p-type material would usher in a new era of technologies. Many reports have failed to live up to their hype; however, the screening by Williamson et al. has predicted [Cu2S2][Ba3Sc2O5] to support a conductivity exceeding 2,000 S cm−1.

Journal article

Gkini K, Balis N, Papadakis M, Verykios A, Skoulikidou M-C, Drivas C, Kennou S, Golomb M, Walsh A, Coutsolelos AG, Vasilopoulou M, Falaras Pet al., 2020, Manganese Porphyrin Interface Engineering in Perovskite Solar Cells, ACS APPLIED ENERGY MATERIALS, Vol: 3, Pages: 7353-7363, ISSN: 2574-0962

Journal article

Rahim W, Skelton JM, Savory CN, Evans IR, Evans JSO, Walsh A, Scanlon DOet al., 2020, Polymorph exploration of bismuth stannate using first-principles phonon mode mapping, CHEMICAL SCIENCE, Vol: 11, Pages: 7904-7909, ISSN: 2041-6520

Journal article

Park SY, Park J-S, Kim BJ, Lee H, Walsh A, Zhu K, Kim DH, Jung HSet al., 2020, Sustainable lead management in halide perovskite solar cells, NATURE SUSTAINABILITY, ISSN: 2398-9629

Journal article

Welch EW, Jung Y-K, Walsh A, Scolfaro L, Zakhidov Aet al., 2020, A density functional theory study on the interface stability between CsPbBr3 and CuI, AIP ADVANCES, Vol: 10

Journal article

Kim S, Hood SN, Park J-S, Whalley LD, Walsh Aet al., 2020, Quick-start guide for first-principles modelling of point defects in crystalline materials, Journal of Physics: Energy, Vol: 2, Pages: 036001-036001

Journal article

Davies DW, Morgan BJ, Scanlon DO, Walsh Aet al., 2020, Low-cost descriptors of electrostatic and electronic contributions to anion redox activity in batteries, IOP SciNotes, Vol: 1, Pages: 024805-024805

Journal article

Morita K, Davies DW, Butler KT, Walsh Aet al., 2020, Modeling the dielectric constants of crystals using machine learning, JOURNAL OF CHEMICAL PHYSICS, Vol: 153, ISSN: 0021-9606

Journal article

Golomb MJ, Calbo J, Bristow JK, Walsh Aet al., 2020, Ligand engineering in Cu(ii) paddle wheel metal-organic frameworks for enhanced semiconductivity, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 8, Pages: 13160-13165, ISSN: 2050-7488

Journal article

Park J-S, Li Z, Wilson JN, Yin W-J, Walsh Aet al., 2020, Hexagonal Stacking Faults Act as Hole-Blocking Layers in Lead Halide Perovskites, ACS ENERGY LETTERS, Vol: 5, Pages: 2231-2233, ISSN: 2380-8195

Journal article

Jones LAH, Linhart WM, Fleck N, Swallow JEN, Murgatroyd PAE, Shiel H, Featherstone TJ, Smiles MJ, Thakur PK, Lee T-L, Hardwick LJ, Alaria J, Jaeckel F, Kudrawiec R, Burton LA, Walsh A, Skelton JM, Veal TD, Dhanak VRet al., 2020, Sn 5s(2) lone pairs and the electronic structure of tin sulphides: A photoreflectance, high-energy photoemission, and theoretical investigation, PHYSICAL REVIEW MATERIALS, Vol: 4, ISSN: 2475-9953

Journal article

Rahim W, Skelton J, Savory C, Evans IR, Evans JSO, Walsh A, Scanlon Det al., 2020, Polymorph Exploration of Bismuth Stannate Using First-principles Phonon Mode Mapping

<jats:p>In this work, we present a new unbiased and efficient quantum chemical method for exploring the potential energy surface of complex crystal structures using theoretically rigorous phonon mode-mapping approach. The method successfully recovers the known experimental phases of the pyrochlore-based Bi&lt;sub&gt;2&lt;/sub&gt;Sn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;, one of the most difficult cases in structural chemistry, which highlights its utility for searching possible transition pathways and identifying global minima for many other challenging systems.&lt;p&gt;&lt;/p&gt;</jats:p>

Journal article

YANG H, Savory C, Morgan B, Scanlon D, Skelton J, Walsh Aet al., 2020, Chemical Trends in the Lattice Thermal Conductivity of Li(Ni,Mn,Co)O<sub>2</sub> (NMC) Battery Cathodes

<jats:p>&lt;div&gt;While the transport of ions and electrons in conventional Li-ion battery cathode&lt;/div&gt;&lt;div&gt;materials is well understood, our knowledge of the phonon (heat) transport is still in its&lt;/div&gt;&lt;div&gt;infancy. We present a first-principles theoretical investigation of the chemical trends&lt;/div&gt;&lt;div&gt;in the phonon frequency dispersion, mode lifetimes, and thermal conductivity in the&lt;/div&gt;&lt;div&gt;series of layered lithium transition-metal oxides Li(NixMnyCoz)O2 (x+y+z = 1). The&lt;/div&gt;&lt;div&gt;oxidation and spin states of the transition metal cations are found to strongly influence&lt;/div&gt;&lt;div&gt;the structural dynamics. Calculations of the thermal conductivity show that LiCoO2&lt;/div&gt;&lt;div&gt;has highest average conductivity of 45.9W m−1 K−1 at T = 300 K and the largest&lt;/div&gt;&lt;div&gt;anisotropy, followed by LiMnO2 with 8.9W m−1 K−1, and LiNiO2 with 6.0W m−1 K−1&lt;/div&gt;&lt;div&gt;The much lower thermal conductivity of LiMnO2 and LiNiO2 is found to be due to 1–2 orders of magnitude shorter phonon lifetimes. We further model the properties of binary and ternary transition metal combinations and show that the thermal conductivity of NMC is suppressed with decreasing Co content and increasing Ni/Mn&lt;/div&gt;&lt;div&gt;content. The thermal conductivity of commercial NMC622 (LiNi0.6Mn0.2Co0.2O2) and NMC111 (LiNi0.33Mn0.33Co0.33O2) compositions are substantially larger than NMC811LiNi0.8Mn0.1Co0.1O2). These results serve as a guide to ongoing work on the designof multi-component battery electrodes with more effective thermal management.&lt;/div&gt;&lt;div&gt;&lt;br&gt;&lt;/div&gt;</jats:p>

Journal article

Golomb M, Calbo J, Bristow JK, Walsh Aet al., 2020, Ligand Engineering in Cu(II) Paddle Wheel Metal-Organic Frameworks for Enhanced Electrical Conductivity

<jats:p>We report the electronic structure of two metal-organic frameworks (MOFs) with copper paddle wheel nodes connected by a N&lt;sub&gt;2&lt;/sub&gt;(C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt; (DABCO) ligand with accessible nitrogen lone pairs. The coordination is predicted, from first-principles density functional theory, to enable electronic pathways that could facilitate charge carrier mobility. Calculated frontier crystal orbitals indicate extended electronic communication in DMOF-1, but not in MOF-649. This feature is confirmed by bandstructure calculations and effective masses of the valence band egde. We explain the origin of the frontier orbitals of both MOFs based on the energy and symmetry alignment of the underlying building blocks. The effects of doping on the bandstructure of MOF-649 are considered. Our findings highlight DMOF-1 as a potential semiconductor with 1D charge carrier mobility along the framework</jats:p>

Journal article

Kim S, Marquez JA, Unold T, Walsh Aet al., 2020, Upper limit to the photovoltaic efficiency of imperfect crystals from first principles, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 13, Pages: 1481-1491, ISSN: 1754-5692

Journal article

Doherty TAS, Winchester AJ, Macpherson S, Johnstone DN, Pareek V, Tennyson EM, Kosar S, Kosasih FU, Anaya M, Abdi-Jalebi M, Andaji-Garmaroudi Z, Wong EL, Madeo J, Chiang Y-H, Park J-S, Jung Y-K, Petoukhoff CE, Divitini G, Man MKL, Ducati C, Walsh A, Midgley PA, Dani KM, Stranks SDet al., 2020, Performance-limiting nanoscale trap clusters at grain junctions in halide perovskites, NATURE, Vol: 580, Pages: 360-+, ISSN: 0028-0836

Journal article

Kim S, Hood SN, van Gerwen P, Whalley L, Walsh Aet al., 2020, CarrierCapture.jl: Anharmonic Carrier Capture

This release includes bug fixes and improvements as suggested as part of the JOSS review process

Software

Kim S, Hood S, van Gerwen P, Whalley L, Walsh Aet al., 2020, CarrierCapture.jl: Anharmonic Carrier Capture, Journal of Open Source Software, Vol: 5, Pages: 2102-2102

Journal article

Kim S, Walsh A, 2020, Comment on "Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole recombination", Publisher: arXiv

Halide perovskites exhibit slow rates of non-radiative electron-holerecombination upon illumination. Chu et al. [Sci. Adv. 6 7, eaaw7453 (2020)]use the results of first-principles simulations to argue that this arises fromthe nature of the crystal vibrations and leads to a breakdown ofShockley-Read-Hall theory. We highlight flaws in their methodology and analysisof carrier capture by point defects in crystalline semiconductors.

Working paper

Davies DW, Savory CN, Frost JM, Scanlon DO, Morgan BJ, Walsh Aet al., 2020, Descriptors for Electron and Hole Charge Carriers in Metal Oxides, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 11, Pages: 438-444, ISSN: 1948-7185

Journal article

Yang RX, Skelton JM, da Silva EL, Frost JM, Walsh Aet al., 2020, Assessment of dynamic structural instabilities across 24 cubic inorganic halide perovskites, JOURNAL OF CHEMICAL PHYSICS, Vol: 152, ISSN: 0021-9606

Journal article

Khenkin MV, Katz EA, Abate A, Bardizza G, Berry JJ, Brabec C, Brunetti F, Bulovic V, Burlingame Q, Di Carlo A, Cheacharoen R, Cheng Y-B, Colsmann A, Cros S, Domanski K, Dusza M, Fell CJ, Forrest SR, Galagan Y, Di Girolamo D, Graetzel M, Hagfeldt A, von Hauff E, Hoppe H, Kettle J, Koebler H, Leite MS, Liu SF, Loo Y-L, Luther JM, Ma C-Q, Madsen M, Manceau M, Matheron M, McGehee M, Meitzner R, Nazeeruddin MK, Nogueira AF, Odabasi C, Osherov A, Park N-G, Reese MO, De Rossi F, Saliba M, Schubert US, Snaith HJ, Stranks SD, Tress W, Troshin PA, Turkovic V, Veenstra S, Visoly-Fisher I, Walsh A, Watson T, Xie H, Yildirim R, Zakeeruddin SM, Zhu K, Lira-Cantu Met al., 2020, Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures, NATURE ENERGY, Vol: 5, Pages: 35-49, ISSN: 2058-7546

Journal article

Silva EL, Santos MC, Skelton JM, Yang T, Santos T, Parker SC, Walsh Aet al., 2020, Electronic and Phonon Instabilities in Bilayer Graphene under Applied External Bias, Pages: 373-382

© 2018 Elsevier Ltd. All rights reserved. We have performed electronic-structure and lattice-dynamics calculations on the AB and AA structures of bilayer graphene. We study the effect of external electric fields and compare results obtained with different levels of theory to existing theoretical and experimental results. Application of an external field to the AB bilayer alters the electronic spectrum, with the bands changing under bias from a parabolic to a "Mexican hat" structure. This results in a semi-metal-To-semiconductor phase transition, with the size of the induced electronic band-gap being tuneable through the field strength. A reduction of continuous symmetry from a hexagonal to a triangular lattice is also evidenced through in-plane electronic charge inhomogeneities between the sublattices. When spin-orbit coupling is turned on for the AB system, we find that the bulk gap decreases, gradually increasing for larger intensities of the bias. Under large bias the energy dispersion recovers the Mexican hat structure, since the energy interaction between the layers balances the coupling interaction. We find that external bias perturbs the harmonic phonon spectra and leads to anomalous behaviour of the out-of-plane flexural ZA and layer-breathing ZO' modes. For the AA system, the electronic and phonon dispersions both remain stable under bias, but the phonon spectrum exhibits zone-center imaginary modes due to layersliding dynamical instabilities.

Conference paper

Kim S, Márquez JA, Unold T, Walsh Aet al., 2020, Upper limit to the photovoltaic efficiency of imperfect crystals from first principles, Energy & Environmental Science, Vol: 13, Pages: 1481-1491, ISSN: 1754-5692

<p>An approach is proposed to predict the impact of point defects on solar cell performance.</p>

Journal article

Crovetto A, Kim S, Fischer M, Stenger N, Walsh A, Chorkendorff I, Vesborg PCKet al., 2020, Assessing the defect tolerance of kesterite-inspired solar absorbers, Energy & Environmental Science, ISSN: 1754-5692

<p>Band tails and defect tolerance in various I<sub>2</sub>–II–IV–V<sub>4</sub> photovoltaic materials can be predicted using computationally-accessible properties and chemical intuition.</p>

Journal article

Morita K, Park J-S, Kim S, Yasuoka K, Walsh Aet al., 2019, Crystal Engineering of Bi2WO6 to Polar Aurivillius-Phase Oxyhalides, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 29155-29161, ISSN: 1932-7447

Journal article

Davies D, Savory C, Frost JM, Scanlon D, Morgan B, Walsh Aet al., 2019, Descriptors for Electron and Hole Charge Carriers in Metal Oxides

<jats:p>&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;Metal oxides can act as insulators, semiconductors or metals depending on theirchemical composition and crystal structure. Metal oxide semiconductors, which support equilibrium populations of electron and hole charge carriers, have widespreadapplications including batteries, solar cells, and display technologies. It is often difficult to predict in advance whether these materials will exhibit localized or delocalizedcharge carriers upon oxidation or reduction. We combine data from first-principlescalculations of the electronic structure and dielectric response of 214 metal oxides topredict the energetic driving force for carrier localization and transport. We assess descriptors based on the carrier effective mass, static polaron binding energy, and Frohlichelectron–phonon coupling. Numerical analysis allows us to assign p and n type transport of a metal oxide to three classes: (i) band transport with high mobility; (ii) smallpolaron transport with low mobility; and (iii) intermediate behaviour. The results ofthis classification agree with observations regarding carrier dynamics and lifetimes andare used to predict 10 candidate p-type oxides.&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;</jats:p>

Journal article

Wang H, Jia J, Wang L, Butler K, Song R, Casillas G, He L, Kherani NP, Perovic DD, Jing L, Walsh A, Dittmeyer R, Ozin GAet al., 2019, Heterostructure Engineering of a Reverse Water Gas Shift Photocatalyst, ADVANCED SCIENCE, Vol: 6

Journal article

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