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Articles by Aron Walsh
Antimony sulfide photovoltaics with high open-circuit voltage not limited by self-trapped excitons
Abstract Sb2S3 is a promising material for low-toxicity, high-stability next-generation photovoltaics, but its device performance is constrained by large open-circuit voltage (VOC) deficits. From recent spectroscopic investigations, it was hypothesized that this arises from self-trapping, limiting VOCs to approximately 800 mV, which is indeed the level nearly all Sb2S3 solar cells have asymptotically approached.
Guiding generative models to uncover diverse and novel crystals via reinforcement learning
Abstract Discovering functional crystalline materials entails navigating an immense combinatorial design space. Although recent advances in generative artificial intelligence have enabled the sampling of chemically plausible compositions and structures, a fundamental challenge remains: the objective misalignment between the likelihood-based sampling in generative modelling and the targeted focus on underexplored regions where novel compounds reside.
Platonic representation of foundation machine learning interatomic potentials
Abstract Foundation machine learning interatomic potentials (MLIPs) have emerged as powerful tools for atomistic simulation, yet different models encode chemical environments in incompatible latent spaces, limiting direct comparison and interoperability. The platonic representation hypothesis suggests that sufficiently capable models converge towards a shared statistical representation of reality.
Key role of oxidizing species driving water oxidation revealed by time-resolved optical and X-ray spectroscopies - Nature Materials
Abstract Oxidation states underpin the understanding of active states, reaction mechanisms and catalytic performance of electrocatalysts. However, determining them at complex solid–liquid interfaces is challenging. Here we use multimodal spectroscopy to investigate polarized iridium oxide (IrOx) electrodes, a model water oxidation catalyst, to identify potential-dependent iridium and oxygen oxidation states.
Guidelines for robust and reproducible point defect simulations in crystals - Nature Reviews Materials
Abstract Many physical properties of functional materials are governed by their impurities rather than their bulk characteristics. Defects in crystals can activate electronic and ionic conductivity, create active centres for catalysis or store information through localized spin configurations. Accurate modelling of defect behaviour is therefore essential for predicting material performance and optimizing functionality across a vast application space.
Operando ultraviolet–visible optical spectroelectrochemistry of surfaces - Nature Reviews Methods Primers
Abstract Ultraviolet–visible spectroelectrochemistry (SEC) is a powerful and accessible operando technique for investigating redox-active interfaces such as electrodes. Its potential has not been fully realized owing to limitations in sensitivity, acquisition speed and analysis workflows. In this Primer, we describe how recent developments in optics, detection hardware and synchronization methods now allow for high-resolution, data-rich SEC measurements.
Learning Crystallographic Disorder: Bridging Prediction and Experiment in Materials Discovery
1 Introduction In recent years, the field of materials discovery has profited immensely from the development of large-scale databases and novel machine learning (ML) tools.[1-5] This advance has catalyzed the development of a variety of discovery workflows, ranging from the computational screening of large databases to structure generation using element substitution methods,[1, 6] random structure search,[4, 7] or (deep) generative models.
Thermodynamics of Sulfur Vacancy Formation in the Chalcogenide Perovskite BaZrS3
1. Introduction Click to copy section linkSection link copied! As an emerging chalcogenide-based photovoltaic material, the perovskite phase of BaZrS3 has promising photovoltaic properties, such as high photoabsorption coefficient, suitable band gap, and defect tolerance. (1−6) Like many sulfides, the synthesis of BaZrS3 can be tracked back to the 1950s; however, difficulties remained in synthesizing samples that have high crystallinity and uniform film formation.
Phase Stability and Transformations in Lead Mixed Halide Perovskites from Machine Learning Force Fields
Special Issue Published as part of Chemistry of Materials special issue “Machine Learning for Materials Chemistry”. I. Introduction Click to copy section linkSection link copied! Lead halide perovskites have the general formula APbX 3 (where A is a monovalent cation and X is a halide). They have emerged as some of the most transformative and versatile materials in modern optoelectronics since their first fabrication half a century ago.
Metal-centred states control carrier lifetimes in transition metal oxide photocatalysts - Nature Chemistry
Abstract Efficient sunlight-to-energy conversion requires materials that can generate long-lived charge carriers upon illumination. However, the targeted design of semiconductors possessing intrinsically long lifetimes remains a key challenge. Here using a series of transition metal oxides, we establish a link between carrier lifetime and electronic configuration in transition metal-based semiconductors.
Defect Tolerance via External Passivation in the Photocatalyst SrTiO3:Al
Introduction Click to copy section linkSection link copied! Strontium titanate (SrTiO3) has long been a prototype water splitting photocatalyst for clean H2 production. (1−3) Various attempts have been made to enhance catalytic activity, including doping, (4−6) morphology tuning, (7−9) and surface modification.
Defect Tolerance via External Passivation in the Photocatalyst SrTiO3:Al
Introduction Click to copy section linkSection link copied! Strontium titanate (SrTiO3) has long been a prototype water splitting photocatalyst for clean H2 production. (1−3) Various attempts have been made to enhance catalytic activity, including doping, (4−6) morphology tuning, (7−9) and surface modification.
Dynamic nanodomains dictate macroscopic properties in lead halide perovskites - Nature Nanotechnology
Abstract Lead halide perovskites have emerged as promising materials for solar energy conversion and X-ray detection owing to their remarkable optoelectronic properties. However, the microscopic origins of their superior performance remain unclear. Here we show that low-symmetry dynamic nanodomains present in the high-symmetry average cubic phases, whose characteristics are dictated by the A-site cation, govern the macroscopic behaviour.
Exploration of crystal chemical space using text-guided generative artificial intelligence - Nature Communications
Abstract The vastness of chemical space presents a long-standing challenge for the exploration of new compounds with pre-determined properties. In materials science, crystal structure prediction has become a mature tool for mapping from composition to structure based on global optimisation techniques. Generative artificial intelligence now offers the means to efficiently navigate larger regions of crystal chemical space informed by structure-property datasets of materials.
Point defect formation at finite temperatures with machine-learning force fields
Point defect formation at finite temperatures with machine-learning force fields Point defects dictate the properties of many functional materials. The standard approach to modelling the thermodynamics of defects relies on a static description, where the change in Gibbs free energy is approximated by the internal energy. This approach has a low computational cost, but ignores contributions from atomic vibrations and structural configurations that can be accessed at finite temperatures.
Multifaceted nature of defect tolerance in halide perovskites and emerging semiconductors - Nature Reviews Chemistry
Abstract Lead halide perovskites (LHPs) have shot to prominence as efficient energy-conversion materials that can be processed using cost-effective fabrication methods. A reason for their exceptional performance is their crystallographic defect tolerance, enabling long charge-carrier lifetimes despite high defect densities. Achieving defect tolerance in broader classes of materials would impact on the semiconductor industry substantially.
WMD-group/SMACT: v3.1.0
<!-- Release notes generated using configuration in .github/release.yml at master --> What's Changed SMACT Metallicity Handling Enhancements by @ryannduma in https://github.com/WMD-group/SMACT/pull/367 Changes to the smact_validity function to allow for early short-circuiting resolving issue #378 by @ryannduma in https://github.com/WMD-group/SMACT/pull/379 Merge develop into master branch by @AntObi in https://github.com/WMD-group/SMACT/pull/392 Updated oxidation.py and its tests by @KingaMas...
WMD-group/SMACT: v3.0.2
<!-- Release notes generated using configuration in .github/release.yml at master --> What's Changed Make the Materials Project tests optional by @AntObi in https://github.com/WMD-group/SMACT/pull/360 Correct the python version in the docs by @KingaMas in https://github.com/WMD-group/SMACT/pull/359 Include crystal space utils in package build by @AntObi in https://github.com/WMD-group/SMACT/pull/361 New Contributors @KingaMas made their first contribution in...
Anomalous in-plane electrical anisotropy in elemental metal nanosheets - Nature Synthesis
Abstract Two-dimensional (2D) elemental metals, often overlooked owing to their lack of switching or dielectric properties, have the potential to exhibit unique properties unachievable by their bulk counterparts if their microstructure can be controlled. Here we propose an electrodeposition method that utilizes a confined 2D template to prepare elemental metal nanosheets with an aligned grain orientation, resulting in an exceptionally high in-plane electrical anisotropy of >103.
Photo-ferroelectric perovskite interfaces for boosting VOC in efficient perovskite solar cells - Nature Communications
Abstract Interface engineering is the core of device optimization, and this is particularly true for perovskite photovoltaics (PVs). The steady improvement in their performance has been largely driven by careful manipulation of interface chemistry to reduce unwanted recombination. Despite that, PVs devices still suffer from unavoidable open circuit voltage (VOC) losses. Here, we propose a different approach by creating a photo-ferroelectric perovskite interface.
Interplay between strain and charge in Cu(In,Ga)Se2 flexible photovoltaics - npj Flexible Electronics
Abstract Flexible and lightweight Cu(In,Ga)Se2 (CIGS) thin-film solar cells are promising for versatile applications, but there is limited understanding of stress-induced changes. In this study, the charge carrier generation and trapping behavior under mechanical stress was investigated using flexible CIGS thin-film solar cells with various alkali treatments. Surface current at the CIGS surface decreased by convex bending, which occurs less with the incorporation of alkali metals.
Cation-eutaxy-enabled III–V-derived van der Waals crystals as memristive semiconductors - Nature Materials
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Abstract Novel two-dimensional semiconductor crystals can exhibit diverse physical properties beyond their inherent semiconducting attributes, making their pursuit paramount. Memristive properties, as exemplars of these attributes, are predominantly manifested in wide-bandgap materials. However, simultaneously harnessing semiconductor properties alongside memristive characteristics to produce memtransistors is challenging.
By Seung-hyun Oh, Giyeok Lee, Taehoon Kim, Narguess Nemati, Kyuho Lee, Jeongmin Kim Verified, Soohyung Park, Jungkil Kim, In Kyu Chung, Hyunyong Choi, Dohun Kim, Jae-Hyun Lee, Heejun Yang, Yunseok Kim, Hong-Gyu Park, Wooyoung Lee, Miso Kim, Dong Won Chun, Myung Joon Han, Aron Walsh, Aloysius Soon, Jinwoo Cheon, Cheolmin Park, Jong-Young Kim, Jee-Hwan Bae
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WMD-group/SMACT: v2.6
<!-- Release notes generated using configuration in .github/release.yml at master --> What's Changed smact_validity function now available to check if a composition would pass the SMACT chemical filters by @AntObi in https://github.com/WMD-group/SMACT/pull/252 [WIP] Add option to use pre-supplied embeddings within SMACT for the dopant_prediction module by @AntObi in https://github.com/WMD-group/SMACT/pull/260 Fix tests by @AntObi in https://github.com/WMD-group/SMACT/pull/233 If eneg None...
Mapping inorganic crystal chemical space
Mapping inorganic crystal chemical space The combination of elements from the Periodic Table defines a vast chemical space. Only a small fraction of these combinations yields materials that occur naturally or are accessible synthetically. Here, we enumerate binary, ternary, and quaternary element and species combinations to produce an extensive library of over 10^10 stoichiometric inorganic compositions.
Band Gap Narrowing by Suppressed Lone-Pair Activity of Bi3+
Download Hi-Res ImageDownload to MS-PowerPointCite This:J. Am. Chem. Soc. 2024, XXXX, XXX RETURN TO ARTICLES ASAPPREVCommunicationNEXT * , Ryu Abe Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan , and Cite this: J. Am. Chem. Soc. 2024, XXXX, XXX .
Band Gap Narrowing by Suppressed Lone-Pair Activity of Bi3+
Download Hi-Res ImageDownload to MS-PowerPointCite This:J. Am. Chem. Soc. 2024, XXXX, XXX RETURN TO ARTICLES ASAPPREVCommunicationNEXT * , Ryu Abe Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan , and Cite this: J. Am. Chem. Soc. 2024, XXXX, XXX .
Open computational materials science - Nature Materials
The materials modelling community is emerging as a champion for reproducible and reusable science. Aron Walsh discusses how FAIR databases, collaborative codes and transparent workflows are advancing this movement. Reproducibility should be a solved problem in computational materials science. In a typical research workflow, a set of input files is transformed into a set of output files using a well-defined algorithm or model.
Monopolizing AI Technology Limits Innovation
The intersection of chemistry and artificial intelligence (AI) is a fascinating area that attracts a lot of attention in both research and industry. We talked to people working in the field about the potential of AI to revolutionize chemical research, but also concerns, (current) limitations, and ethical implications for chemical applications. We also asked for ideas to try or experiment with, as well as useful articles and videos for beginners and advanced users.
Low-Cost Vibrational Free Energies in Solid Solutions with Machine Learning Force Fields
Download Hi-Res ImageDownload to MS-PowerPointCite This:J. Phys. Chem. Lett.
Metal Halide Thermoelectrics: Prediction of High-Performance ${\mathrm{Cs}\mathrm{Cu}}_{2}{\mathrm{I}}_{3}$
Popular Summary High-performance thermoelectric materials have been traditionally based on heavy and toxic elements with low crustal abundance. A new generation of materials is emerging that has the potential to push the limits of the figure of merit ZT. The family of metal halides has been rapidly expanding with applications in domains such as photovoltaics, information storage, and radiation sensors.
Metal-Organic Framework Supercapacitors: Challenges and Opportunities
1 Introduction Clean energy storage technologies are critical to transform the fossil fuel-based transportation sector and to store energy from intermittent renewable sources. Supercapacitors have gained much attention due to their fast charging and discharging times, and their long cycle lifetimes.[1] These electrochemical devices usually consist of two solid electrodes, an ion-permeable separator, and a liquid electrolyte.
Models of orientational disorder in hybrid organic-inorganic piezoelectric materials
Models of orientational disorder in hybrid organic-inorganic piezoelectric materials Abstract Hybrid organic-inorganic materials show potential as flexible and Pb-free piezoelectric materials, but ferroelectric-to-paraelectric phase transitions are responsible for a loss of properties at increased temperatures.
Unraveling chirality transfer mechanism by structural isomer-derived hydrogen bonding interaction in 2D chiral perovskite - Nature Communications
Abstract In principle, the induced chirality of hybrid perovskites results from symmetry-breaking within inorganic frameworks. However, the detailed mechanism behind the chirality transfer remains unknown due to the lack of systematic studies. Here, using the structural isomer with different functional group location, we deduce the effect of hydrogen-bonding interaction between two building blocks on the degree of chirality transfer in inorganic frameworks.
Orbital Engineering in Sillén-Aurivillius Phase Bismuth Oxyiodide Photocatalysts through Interlayer Interactions
Multicomponent inorganic compounds containing post-transition-metal cations such as Sn, Pb, and Bi are a promising class of photocatalysts, but their structure–property relationships remain difficult to decipher. Here, we report three novel bismuth-based layered oxyiodides, the Sillén–Aurivillius phase Bi4NbO8I, Bi5BaTi3O14I, and Bi6NbWO14I. We show that the interlayer Bi–Bi interaction is a key to controlling the electronic structure.
Identifying the ground state structures of point defects in solids - npj Computational Materials
Abstract Point defects are a universal feature of crystals. Their identification is addressed by combining experimental measurements with theoretical models. The standard modelling approach is, however, prone to missing the ground state atomic configurations associated with energy-lowering reconstructions from the idealised crystallographic environment. Missed ground states compromise the accuracy of calculated properties.
An embedded interfacial network stabilizes inorganic CsPbI3 perovskite thin films - Nature Communications
Materials preparation Perovskite thin films: Cesium iodide (CsI, 99.9%) was purchased from Fisher Scientific. Lead iodide (PbI2, 99.9%), lead bromide (PbBr2, 99.9%), anhydrous dimethyl sulfoxide (DMSO) and gamma-Butyrolactone (GBL) were purchased from Sigma-Aldrich. The perovskite precursor powders were weighed and treated at 80 °C under vacuum in a vacuum oven for 2 h to remove any trapped moisture before use.
Concluding remarks: Emerging Inorganic Materials in Thin-Film Photovoltaics
Concluding remarks: Emerging Inorganic Materials in Thin-Film Photovoltaics Abstract A personal perspective is given on the major results, themes and trends from the Faraday Discussion on emerging materials for solar energy technologies.
Impact of metastable defect structures on carrier recombination in solar cells
Impact of metastable defect structures on carrier recombination in solar cells† Seán R. Kavanagh, *ab David O. Scanlon, a Aron Walsh ac and Christoph Freysoldt d Abstract The efficiency of a solar cell is often limited by electron–hole recombination mediated by defect states within the band gap of the photovoltaic (PV) semiconductor. The Shockley–Read–Hall (SRH) model considers a static trap that can successively capture electrons and holes.
Low Barrier for Exciton Self-Trapping Enables High Photoluminescence Quantum Yield in Cs3Cu2I5
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Evolutionary exploration of polytypism in lead halide perovskites
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Prediction of high thermoelectric performance in the low-dimensional metal halide Cs3Cu2I5 - npj Computational Materials
Abstract 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.
Colloidal Nano-MOFs Nucleate and Stabilize Ultra-Small Quantum Dots of Lead Bromide Perovskites
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[2008.08959] Perovskite-Inspired Materials for Photovoltaics -- From Design to Devices
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Dielectric and ferroic properties of metal halide perovskites
Semiconducting halide perovskite materials have attracted intense research interest over the past five years due to the potential for inexpensive solution processing and desirable optoelectronic properties for photovoltaic (PV) and light emission applications.1–31. S. D. Stranks, P. K. Nayak, W. Zhang, T. Stergiopoulos, and H. J. Snaith, Angew. Chem., Int. Ed. 54, 3240 (2015). https://doi.org/10.1002/anie.2014102142. A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, J. Am. Chem. Soc. 131, 6050 (2009).
Prediction on the existence and chemical stability of cuprous fluoride
Prediction on the existence and chemical stability of cuprous fluoride Aron Walsh,*a C. Richard A. Catlow,b Raimondas Galvelis,b David O. Scanlon,b Florian Schiffmann,b Alexey A. Sokolb and Scott M.
Ligand engineering in Cu(II) paddle wheel metal-organic frameworks for enhanced semiconductivity
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Upper limit to the photovoltaic efficiency of imperfect crystals from first principles
Upper limit to the photovoltaic efficiency of imperfect crystals from first principles† The Shockley–Queisser (SQ) limit provides a convenient metric for predicting light-to-electricity conversion efficiency of a solar cell based on the band gap of the light-absorbing layer. In reality, few materials approach this radiative limit. We develop a formalism and computational method to predict the maximum photovoltaic efficiency of imperfect crystals from first principles.
Assessment of dynamic structural instabilities across 24 cubic inorganic halide perovskites
I. INTRODUCTION Since the discovery of photoconductivity in the cesium lead halides (CsPbX3 [X = Cl, Br, I]),11. C. K. Møller, Nature 182, 1436 (1958). https://doi.org/10.1038/1821436a0 the semiconducting properties of halide perovskites have attracted significant research attention, including analogous compounds based on Sn and Ge.2–42. J. D. Donaldson, S. Hadjiminolis, J. Silver, and S. D. Ross, J. Chem. Soc., Dalton Trans. 1975, 1500. https://doi.org/10.1039/dt97500015003. M. Kaupp, K. Syassen, H.-G.
[1912.07889] Upper limit to the photovoltaic efficiency of imperfect crystals
Authors:Sunghyun Kim, José A. Márquez, 2 Thomas Unold, Aron Walsh (Submitted on 17 Dec 2019) Abstract: The Shockley-Queisser (SQ) limit provides a convenient metric for predicting light-to-electricity conversion efficiency of a solar cell based on the band gap of the light-absorbing layer. In reality, few materials approach this radiative limit. We develop a formalism and a computational method to predict the maximum photovoltaic efficiency of imperfect crystals from first principles.
Highly Anisotropic Thermal Transport in LiCoO2
LiCoO2 is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li+ and CoO2- layers along the hexagonal <0001> axis. It is well established that ionic and electronic conduction is highly anisotropic; however, little is known regarding heat transport. We analyse the phonon dispersion and lifetimes of LiCoO2 using anharmonic lattice dynamics based on quantum chemical force constants.
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