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

454 results found

Morgan L, Mercer M, Bhandari A, Peng C, Islam MM, Yang H, Holland JO, Coles SW, Sharpe R, Walsh A, Morgan BJ, Kramer D, Islam SM, Hoster H, Edge JS, Skylaris C-Ket al., 2021, Pushing the boundaries of lithium battery research with atomistic modelling on different scales, Progress in Energy

<jats:title>Abstract</jats:title> <jats:p>Computational modelling is a vital tool in the research of batteries and their component materials. Atomistic models are key to building truly physics-based models of batteries and form the foundation of the multiscale modelling chain, leading to more robust and predictive models. These models can be applied to fundamental research questions with high predictive accuracy. For example, they can be used to predict new behaviour not currently accessible by experiment, for reasons of cost, safety, or throughput. Atomistic models are useful for quantifying and evaluating trends in experimental data, explaining structure-property relationships, and informing materials design strategies and libraries. In this review, we showcase the most prominent atomistic modelling methods and their application to electrode materials, liquid and solid electrolyte materials, and their interfaces, highlighting the diverse range of battery properties that can be investigated. Furthermore, we link atomistic modelling to experimental data and higher scale models such as continuum and control models. We also provide a critical discussion on the outlook of these materials and the main challenges for future battery research.</jats:p>

Journal article

Krenzer G, Kim C-E, Tolborg K, Morgan BJ, Walsh Aet al., 2021, Anharmonic lattice dynamics of superionic lithium nitride, JOURNAL OF MATERIALS CHEMISTRY A, ISSN: 2050-7488

Journal article

Yang J-M, Jung Y-K, Lee J-H, Kim YC, Kim S-Y, Seo S, Park D-A, Kim J-H, Jeong S-Y, Han I-T, Park J-H, Walsh A, Park N-Get al., 2021, Asymmetric carrier transport in flexible interface-type memristor enables artificial synapses with sub-femtojoule energy consumption, NANOSCALE HORIZONS, Vol: 6, Pages: 987-997, ISSN: 2055-6756

Journal article

Krajewska CJ, Kavanagh SR, Zhang L, Kubicki DJ, Dey K, Galkowski K, Grey CP, Stranks SD, Walsh A, Scanlon DO, Palgrave RGet al., 2021, Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(ii)/Sn(iv) doping, CHEMICAL SCIENCE, Vol: 12, Pages: 14686-14699, ISSN: 2041-6520

Journal article

Huang Y-T, Kavanagh SR, Scanlon DO, Walsh A, Hoye RLZet al., 2021, Perovskite-inspired materials for photovoltaics and beyond-from design to devices (vol 32, 132004, 2021), NANOTECHNOLOGY, Vol: 32, ISSN: 0957-4484

Journal article

Jung Y-K, Kim S, Kim YC, Walsh Aet al., 2021, Low Barrier for Exciton Self-Trapping Enables High Photoluminescence Quantum Yield in Cs3Cu2I5, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 12, Pages: 8447-8452, ISSN: 1948-7185

Journal article

Simenas M, Balciunas S, Svirskas S, Kinka M, Ptak M, Kalendra V, Gagor A, Szewczyk D, Sieradzki A, Grigalaitis R, Walsh A, Maczka M, Banys Jet al., 2021, Phase Diagram and Cation Dynamics of Mixed MA(1-x)FA(x)PbBr(3) Hybrid Perovskites, CHEMISTRY OF MATERIALS, Vol: 33, Pages: 5926-5934, ISSN: 0897-4756

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Li Z, Park J-S, Walsh A, 2021, Evolutionary exploration of polytypism in lead halide perovskites, CHEMICAL SCIENCE, Vol: 12, Pages: 12165-12173, ISSN: 2041-6520

Journal article

Harnett-Caulfield L, Walsh A, 2021, Assessment of interstitial potentials for rapid prediction of absolute band energies in crystals, JOURNAL OF CHEMICAL PHYSICS, Vol: 155, ISSN: 0021-9606

Journal article

Kavanagh SR, Savory CN, Scanlon DO, Walsh Aet al., 2021, Hidden spontaneous polarisation in the chalcohalide photovoltaic absorber Sn2SbS2I3, MATERIALS HORIZONS, Vol: 8, ISSN: 2051-6347

Journal article

Gittins JW, Balhatchet CJ, Chen Y, Liu C, Madden DG, Britto S, Golomb MJ, Walsh A, Fairen-Jimenez D, Dutton SE, Forse ACet al., 2021, Insights into the electric double-layer capacitance of two-dimensional electrically conductive metal-organic frameworks, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 9, Pages: 16006-16015, ISSN: 2050-7488

Journal article

Whalley LD, van Gerwen P, Frost JM, Kim S, Hood SN, Walsh Aet al., 2021, Giant Huang-Rhys Factor for Electron Capture by the Iodine Intersitial in Perovskite Solar Cells, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 143, Pages: 9123-9128, ISSN: 0002-7863

Journal article

Artrith N, Butler KT, Coudert F-X, Han S, Isayev O, Jain A, Walsh Aet al., 2021, Best practices in machine learning for chemistry comment, NATURE CHEMISTRY, Vol: 13, Pages: 505-508, ISSN: 1755-4330

Journal article

Walsh A, 2021, Correcting the corrections for charged defects in crystals, NPJ COMPUTATIONAL MATERIALS, Vol: 7

Journal article

Protesescu L, Calbo J, Williams K, Tisdale W, Walsh A, Dinca Met al., 2021, Colloidal nano-MOFs nucleate and stabilize ultra-small quantum dots of lead bromide perovskites, Chemical Science, Vol: 12, Pages: 6129-6135, ISSN: 2041-6520

The development of synthetic routes to access stable, ultra-small (i.e. <5 nm) lead halide perovskite (LHP) quantum dots (QDs) is of fundamental and technological interest. The considerable challenges include the high solubility of the ionic LHPs in polar solvents and aggregation to form larger particles. Here, we demonstrate a simple and effective host–guest strategy for preparing ultra-small lead bromide perovskite QDs through the use of nano-sized MOFs that function as nucleating and host sites. Cr3O(OH)(H2O)2(terephthalate)3 (Cr-MIL-101), made of large mesopore-sized pseudo-spherical cages, allows fast and efficient diffusion of perovskite precursors within its pores, and promotes the formation of stable, ∼3 nm-wide lead bromide perovskite QDs. CsPbBr3, MAPbBr3 (MA+ = methylammonium), and (FA)PbBr3 (FA+ = formamidinium) QDs exhibit significantly blue-shifted emission maxima at 440 nm, 446 nm, and 450 nm, respectively, as expected for strongly confined perovskite QDs. Optical characterization and composite modelling confirm that the APbBr3 (A = Cs, MA, FA) QDs owe their stability within the MIL-101 nanocrystals to both short- and long-range interfacial interactions with the MOF pore walls.

Journal article

Zakutayev A, Major JD, Hao X, Walsh A, Tang J, Todorov TK, Wong LH, Saucedo Eet al., 2021, Emerging inorganic solar cell Efficiency Tables (version 2), Journal of Physics: Energy, Vol: 3, Pages: 1-18, ISSN: 2515-7655

This paper presents the second version of the efficiency tables of materials considered as emerging inorganic absorbers for photovoltaic solar cell technologies. The materials collected in these tables are selected based on their progress in recent years, and their demonstrated potential as future photovoltaic absorbers. The first part of the paper consists of the guidelines for the inclusion of the different technologies in this paper, the verification means used by the authors, and recommendation for measurement best practices. The second part details the highest world-class certified solar cell efficiencies, and the highest non-certified cases (some independently confirmed). The third part highlights the new entries including the record efficiencies, as well as new materials included in this version of the tables. The final part is dedicated to review a specific aspect of materials research that the authors consider of high relevance for the scientific community. In this version of the efficiency tables, we are including an overview of the latest progress in quasi one-dimensional absorbers, such as antimony chalcogenides, for photovoltaic applications.

Journal article

Jung Y-K, Han IT, Kim YC, Walsh Aet al., 2021, Prediction of high thermoelectric performance in the low-dimensional metal halide Cs3Cu2I5, npj Computational Materials, Vol: 7, Pages: 1-6, ISSN: 2057-3960

Metal halides have emerged as a new generation of semiconductors with applications ranging from solar cells to chemical sensors. We assess the thermoelectric potential of Cs3Cu2I5, which has a crystal structure formed of zero-dimensional [Cu2I5]3− anionic clusters that are separated by Cs+ counter cations. We find the compound exhibits the characteristics of a phonon-glass electron-crystal with a large imbalance in the conduction of heat and electrons predicted from first-principles transport theory. Strong anharmonic phonon–phonon scattering results in short-lived acoustic vibrations and an ultra-low lattice thermal conductivity (<0.1 W m−1 K−1). The dispersive conduction band leads to a high electron mobility (>10 cm2 V−1 s−1). For an n-type crystal at 600 K, a thermoelectric figure-of-merit ZT of 2.6 is found to be accessible, which for a cold source of 300 K corresponds to a thermodynamic heat-to-electricity conversion efficiency of 15%.

Journal article

Bainglass E, Walsh A, Huda MN, 2021, BiSbWO6: Properties of a mixed 5s/6s lone-pair-electron system, Chemical Physics, Vol: 544, Pages: 1-8, ISSN: 0301-0104

We investigate the behavior of lone-pair electrons in a mixed Sb(5s)/Bi(6s) crystal-environment. Density functional theory is used to calculate the electronic properties of Sb-alloyed-Bi2WO6 and to study the effects of introducing Sb 5s orbitals to the band structure. The band edge positions, partial charge analyses, and band decomposed charge densities of BiSbWO6 are used to explain the observed trends in relative stabilities and band edge shifts. To isolate the role of the mixed lone-pair, we considered WO3 as a control model. We find that local distortions caused by Sb 5s lone-pair electrons lead to upshifts in both valence and conduction band edges.

Journal article

Jedlicka E, Wang J, Mutch J, Jung Y-K, Went P, Mohammed J, Ziffer M, Giridharagopal R, Walsh A, Chu J-H, Ginger DSet al., 2021, Bismuth doping alters structural phase transitions in methylammonium lead tribromide single crystals., Journal of Physical Chemistry Letters, Vol: 12, Pages: 2749-2755, ISSN: 1948-7185

We study the effects of bismuth doping on the crystal structure and phase transitions in single crystals of the perovskite semiconductor methylammonium lead tribromide, MAPbBr3. By measuring the temperature-dependent specific heat capacity (C p ), we find that as the Bi doping increases, the phase transition assigned to the cubic to tetragonal phase boundary decreases in temperature. Furthermore, after doping we observe one phase transition between 135 and 155 K, in contrast to two transitions observed in the undoped single crystal. These results appear strikingly similar to previously reported effects of mechanical pressure on perovskite crystal structure. Using X-ray diffraction, we show that the lattice constant decreases as Bi is incorporated into the crystal, as predicted by density functional theory. We propose that bismuth substitutional doping on the lead site is dominant, resulting in BiPb+ centers that induce compressive chemical strain that alters the crystalline phase transitions.

Journal article

Kavanagh SR, Walsh A, Scanlon DO, 2021, Rapid recombination by cadmium vacancies in CdTe, ACS Energy Letters, Vol: 6, Pages: 1392-1398, ISSN: 2380-8195

CdTe is currently the largest thin-film photovoltaic technology. Non-radiative electron–hole recombination reduces the solar conversion efficiency from an ideal value of 32% to a current champion performance of 22%. The cadmium vacancy (VCd) is a prominent acceptor species in p-type CdTe; however, debate continues regarding its structural and electronic behavior. Using ab initio defect techniques, we calculate a negative-U double-acceptor level for VCd, while reproducing the VCd1– hole–polaron, reconciling theoretical predictions with experimental observations. We find the cadmium vacancy facilitates rapid charge-carrier recombination, reducing maximum power-conversion efficiency by over 5% for untreated CdTe—a consequence of tellurium dimerization, metastable structural arrangements, and anharmonic potential energy surfaces for carrier capture.

Journal article

Park J-S, Walsh A, 2021, Modeling grain boundaries in polycrystalline halide perovskite solar cells, Annual Review of Condensed Matter Physics, Vol: 12, Pages: 95-109, ISSN: 1947-5454

Solar cells are semiconductor devices that generate electricity through charge generation upon illumination. For optimal device efficiency, the photogenerated carriers must reach the electrical contact layers before they recombine. A deep understanding of the recombination process and transport behavior is essential to design better devices. Halide perovskite solar cells are commonly made of a polycrystalline absorber layer, but there is no consensus on the nature and role of grain boundaries. This review concerns theoretical approaches for the investigation of extended defects. We introduce recent computational studies on grain boundaries, and their influence on point-defect distributions, in halide perovskite solar cells. We conclude with a discussion of future research directions.

Journal article

Jaskaniec S, Kavanagh SR, Coelho J, Ryan S, Hobbs C, Walsh A, Scanlon DO, Nicolosi Vet al., 2021, Solvent engineered synthesis of layered SnO for high-performance anodes, npj 2D Materials and Applications, Vol: 5, Pages: 1-9, ISSN: 2397-7132

Batteries are the most abundant form of electrochemical energy storage. Lithium and sodium ion batteries account for a significant portion of the battery market, but high-performance electrochemically active materials still need to be discovered and optimized for these technologies. Recently, tin(II) oxide (SnO) has emerged as a highly promising battery electrode. In this work, we present a facile synthesis method to produce SnO microparticles whose size and shape can be tailored by changing the solvent nature. We study the complex relationship between wet-chemistry synthesis conditions and resulting layered nanoparticle morphology. Furthermore, high-level electronic structure theory, including dispersion corrections to account for van der Waals forces, is employed to enhance our understanding of the underlying chemical mechanisms. The electronic vacuum alignment and surface energies are determined, allowing the prediction of the thermodynamically favoured crystal shape (Wulff construction) and surface-weighted work function. Finally, the synthesized nanomaterials were tested as Li-ion battery anodes, demonstrating significantly enhanced electrochemical performance for morphologies obtained from specific synthesis conditions.

Journal article

Rigter SA, Quinn XL, Kumar RE, Fenning DP, Massonnet P, Ellis SR, Heeren RMA, Svane KL, Walsh A, Garnett ECet al., 2021, Passivation properties and formation mechanism of amorphous halide perovskite thin films, Advanced Functional Materials, Vol: 31, Pages: 1-10, ISSN: 1616-301X

Lead halide perovskites are among the most exciting classes of optoelectronic materials due to their unique ability to form high‐quality crystals with tunable bandgaps in the visible and near‐infrared using simple solution precipitation reactions. This facile crystallization is driven by their ionic nature; just as with other salts, it is challenging to form amorphous halide perovskites, particularly in thin‐film form where they can most easily be studied. Here, rapid desolvation promoted by the addition of acetate precursors is shown as a general method for making amorphous lead halide perovskite films with a wide variety of compositions, including those using common organic cations (methylammonium and formamidinium) and anions (bromide and iodide). By controlling the amount of acetate, it is possible to tune from fully crystalline to fully amorphous films, with an interesting intermediate state consisting of crystalline islands embedded in an amorphous matrix. The amorphous lead halide perovskite has a large and tunable optical bandgap. It improves the photoluminescence quantum yield and lifetime of incorporated crystalline perovskite, opening up the intriguing possibility of using amorphous perovskite as a passivating contact, as is currently done in record efficiency silicon solar cells.

Journal article

Okenyi MTO, Ratcliff LE, Walsh A, 2021, Multi-phonon proton transfer pathway in a molecular organic ferroelectric crystal, Physical Chemistry Chemical Physics, Vol: 23, Pages: 2885-2890, ISSN: 1463-9076

While the majority of ferroelectrics research has been focused on inorganic ceramics, molecular ferroelectrics can also combine large spontaneous polarization with high Curie temperatures. However, the microscopic mechanism of their ferroelectric switching is not fully understood. We explore proton tautomerism in the prototypical case of croconic acid, C5O5H2. In order to determine how efficiently ferroelectricity in croconic acid is described in terms of its Γ-point phonon modes, the minimum energy path between its structural ground states is approximated by projection onto reduced basis sets formed from subsets of these modes. The potential energy curve along the minimum energy path was found to be sensitive to the order of proton transfer, which requires a large subset (≳8) of the modes to be approximated accurately. Our findings suggest rules for the construction of effective Hamiltonians to describe proton transfer ferroelectrics.

Journal article

Huang Y-T, Kavanagh S, Scanlon D, Walsh A, Hoye Ret al., 2021, Perovskite-inspired materials for photovoltaics and beyond – from design to devices, Nanotechnology, Vol: 32, Pages: 1-60, ISSN: 0957-4484

NanotechnologyACCEPTED MANUSCRIPT • The following article is Open accessPerovskite-Inspired Materials for Photovoltaics and Beyond – From Design to DevicesYi-Teng Huang1, Seán R. Kavanagh2, David O Scanlon3, Aron Walsh4 and Robert Hoye5Accepted Manuscript online 1 December 2020 • © 2020 The Author(s). Published by IOP Publishing Ltd.What is an Accepted Manuscript?Download Accepted Manuscript PDFDownload PDFArticle has an altmetric score of 6Turn on MathJaxShare this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on MendeleyArticle informationAbstractLead-halide perovskites have demonstrated astonishing increases in power conversion efficiency in photovoltaics over the last decade. The most efficient perovskite devices now outperform industry-standard multi-crystalline silicon solar cells, despite the fact that perovskites are typically grown at low temperature using simple solution-based methods. However, the toxicity of lead and its ready solubility in water are concerns for widespread implementation. These challenges, alongside the many successes of the perovskites, have motivated significant efforts across multiple disciplines to find lead-free and stable alternatives which could mimic the ability of the perovskites to achieve high performance with low temperature, facile fabrication methods. This Review discusses the computational and experimental approaches that have been taken to discover lead-free perovskite-inspired materials, and the recent successes and challenges in synthesizing these compounds. The atomistic origins of the extraordinary performance exhibited by lead-halide perovskites in photovoltaic devices is discussed, alongside the key challenges in engineering such high-performance in alternative, next-generation materials. Beyond photovoltaics, this Review discusses the impact perovskite-inspired materials have had in spurring efforts to apply new materials i

Journal article

Bibi A, Lee I, Nah Y, Allam O, Kim H, Quan LN, Tang J, Walsh A, Jang SS, Sargent EH, Kim DHet al., 2021, Lead-free halide double perovskites: Toward stable and sustainable optoelectronic devices, Materials Today, ISSN: 1369-7021

In recent years, metal halide perovskites (MHPs) have attracted attention as semiconductors that achieve desirable properties for optoelectronic devices. However, two challenges—instability and the regulated nature of Pb —remain to be addressed with commercial applications. The development of Pb-free halide double perovskite (HDP) materials has gained interest and attention as a result. This family offers potential in the field of optoelectronic devices through flexible material designs and compositional adjustments. We highlight recent progress and development in halide double perovskites and encompass the synthesis, optoelectronic properties, and engineering of the electronic structures of these materials along with their applications in optoelectronic devices. Computational and data-driven statistical methods can also be used to explore mechanisms and discover promising candidate double perovskites.

Journal article

Reichert S, An Q, Woo Y-W, Walsh A, Vaynzof Y, Deibel Cet al., 2020, Probing the ionic defect landscape in halide perovskite solar cells, Nature Communications, Vol: 11, Pages: 1-10, ISSN: 2041-1723

Point defects in metal halide perovskites play a critical role in determining their properties and optoelectronic performance; however, many open questions remain unanswered. In this work, we apply impedance spectroscopy and deep-level transient spectroscopy to characterize the ionic defect landscape in methylammonium lead triiodide (MAPbI3) perovskites in which defects were purposely introduced by fractionally changing the precursor stoichiometry. Our results highlight the profound influence of defects on the electronic landscape, exemplified by their impact on the device built-in potential, and consequently, the open-circuit voltage. Even low ion densities can have an impact on the electronic landscape when both cations and anions are considered as mobile. Moreover, we find that all measured ionic defects fulfil the Meyer–Neldel rule with a characteristic energy connected to the underlying ion hopping process. These findings support a general categorization of defects in halide perovskite compounds.

Journal article

Kobayashi Y, Hirata K, Hood SN, Yang H, Walsh A, Matsushita Y, Ishioka Ket al., 2020, Crystal structure and metallization mechanism of the pi-radical metal TED (vol 11, pg 11699, 2020), Chemical Science, Vol: 11, Pages: 11945-11946, ISSN: 2041-6520

Correction for ‘Crystal structure and metallization mechanism of the π-radical metal TED’ by Yuka Kobayashi et al., Chem. Sci., 2020, DOI: 10.1039/d0sc03521a.

Journal article

Li Z, Kavanagh S, Napari M, Palgrave RG, Abdi-Jalebi M, Andaji-Garmaroudi Z, Davies DW, Laitinen M, Julin J, Isaacs MA, Friend RH, Scanlon DO, Walsh A, Hoye Ret al., 2020, Bandgap lowering in mixed alloys ofCs2Ag(SbxBi1-x)Br6 double perovskite thin films, Journal of Materials Chemistry A, Vol: 8, Pages: 21780-21788, ISSN: 2050-7488

Halide double perovskites have gained significant attention, owing to their composition of low-toxicity elements, stability in air and long charge-carrier lifetimes. However, most double perovskites, including Cs2AgBiBr6, have wide bandgaps, which limits photoconversion efficiencies. The bandgap can be reduced through alloying with Sb3+, but Sb-rich alloys are difficult to synthesize due to the high formation energy of Cs2AgSbBr6, which itself has a wide bandgap. We develop a solution-based route to synthesize phase-pure Cs2Ag(SbxBi1−x)Br6 thin films, with the mixing parameter x continuously varying over the entire composition range. We reveal that the mixed alloys (x between 0.5 and 0.9) demonstrate smaller bandgaps than the pure Sb- and Bi-based compounds. The reduction in the bandgap of Cs2AgBiBr6 achieved through alloying (170 meV) is larger than if the mixed alloys had obeyed Vegard's law (70 meV). Through in-depth computations, we propose that bandgap lowering arises from the type II band alignment between Cs2AgBiBr6 and Cs2AgSbBr6. The energy mismatch between the Bi and Sb s and p atomic orbitals, coupled with their non-linear mixing, results in the alloys adopting a smaller bandgap than the pure compounds. Our work demonstrates an approach to achieve bandgap reduction and highlights that bandgap bowing may be found in other double perovskite alloys by pairing together materials forming a type II band alignment.

Journal article

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