Publications
559 results found
Tolborg K, Klarbring J, Ganose AM, et al., 2022, Free energy predictions for crystal stability and synthesisability
<jats:p>What is the likelihood that a hypothetical material - the combination of a composition and crystal structure - can be formed? Underpinning the reliability of predictions for local or global crystal stability is the choice of thermodynamic potential. Here, we discuss recent advances in free energy descriptions for crystals including both harmonic and anharmonic phonon contributions to the vibrational entropy. We critically discuss some of the techniques and descriptors, including data-driven machine learning approaches, being developed to assess the stability and synthesisability of solids. Avenues are highlighted that deserve further attention including thermodynamic and kinetic factors that govern the accessibility of metastable structures away from equilibrium.</jats:p>
Rakowski R, Fisher W, Calbo J, et al., 2022, High Power Irradiance Dependence of Charge Species Dynamics in Hybrid Perovskites and Kinetic Evidence for Transient Vibrational Stark Effect in Formamidinium, NANOMATERIALS, Vol: 12
Wang Y, Kavanagh SR, Burgues-Ceballos I, et al., 2022, Cation disorder engineering yields AgBiS<sub>2</sub> nanocrystals with enhanced optical absorption for efficient ultrathin solar cells (vol 16, pg 235, 2022), NATURE PHOTONICS, Vol: 16, Pages: 396-396, ISSN: 1749-4885
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- Citations: 2
Yang J-M, Lee J-H, Jung Y-K, et al., 2022, Mixed-Dimensional Formamidinium Bismuth Iodides Featuring In-Situ Formed Type-I Band Structure for Convolution Neural Networks, ADVANCED SCIENCE, Vol: 9
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- Citations: 4
Gu GH, Jang J, Noh J, et al., 2022, Perovskite synthesizability using graph neural networks, NPJ COMPUTATIONAL MATERIALS, Vol: 8
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- Citations: 9
Yun J, Tan J, Jung Y-K, et al., 2022, Interfacial Dipole Layer Enables High-Performance Heterojunctions for Photoelectrochemical Water Splitting, ACS ENERGY LETTERS, Vol: 7, Pages: 1392-1402, ISSN: 2380-8195
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- Citations: 9
Verma S, Rivera M, Scanlon DO, et al., 2022, Machine learned calibrations to high-throughput molecular excited state calculations., Journal of Chemical Physics, Vol: 156, Pages: 134116-134116, ISSN: 0021-9606
Understanding the excited state properties of molecules provides insight into how they interact with light. These interactions can be exploited to design compounds for photochemical applications, including enhanced spectral conversion of light to increase the efficiency of photovoltaic cells. While chemical discovery is time- and resource-intensive experimentally, computational chemistry can be used to screen large-scale databases for molecules of interest in a procedure known as high-throughput virtual screening. The first step usually involves a high-speed but low-accuracy method to screen large numbers of molecules (potentially millions), so only the best candidates are evaluated with expensive methods. However, use of a coarse first-pass screening method can potentially result in high false positive or false negative rates. Therefore, this study uses machine learning to calibrate a high-throughput technique [eXtended Tight Binding based simplified Tamm-Dancoff approximation (xTB-sTDA)] against a higher accuracy one (time-dependent density functional theory). Testing the calibration model shows an approximately sixfold decrease in the error in-domain and an approximately threefold decrease in the out-of-domain. The resulting mean absolute error of ∼0.14 eV is in line with previous work in machine learning calibrations and out-performs previous work in linear calibration of xTB-sTDA. We then apply the calibration model to screen a 250k molecule database and map inaccuracies of xTB-sTDA in chemical space. We also show generalizability of the workflow by calibrating against a higher-level technique (CC2), yielding a similarly low error. Overall, this work demonstrates that machine learning can be used to develop a cost-effective and accurate method for large-scale excited state screening, enabling accelerated molecular discovery across a variety of disciplines.
Twyman NM, Walsh A, Buonassisi T, 2022, Environmental stability of crystals: a greedy screening, Chemistry of Materials, Vol: 34, Pages: 2545-2552, ISSN: 0897-4756
Discovering materials that are environmentally stable and also exhibit the necessary collection of properties required for a particular application is a perennial challenge in materials science. Herein, we present an algorithm to rapidly screen materials for their thermodynamic stability in a given environment, using a greedy approach. The performance was tested against the standard energy above the hull stability metric for inert conditions. Using data of 126 320 crystals, the greedy algorithm was shown to estimate the driving force for decomposition with a mean absolute error of 39.5 meV/atom, giving it sufficient resolution to identify stable materials. To demonstrate the utility outside of a vacuum, the in-oxygen stability of 39 654 materials was tested. The enthalpy of oxidation was found to be largely exothermic. Further analysis showed that 1438 of these materials fall into the range required for self-passivation based on the Pilling–Bedworth ratio.
Michaels H, Golomb MJ, Kim BJ, et al., 2022, Copper coordination polymers with selective hole conductivity, Journal of Materials Chemistry A, Vol: 10, Pages: 9582-9591, ISSN: 2050-7488
Emerging technologies in solar energy will be critical in enabling worldwide society in overcoming the present energy challenges and reaching carbon net zero. Inefficient and unstable charge transport materials limit the current emerging energy conversion and storage technologies. Low-dimensional coordination polymers represent an alternative, unprecedented class of charge transport materials, comprised of molecular building blocks. Here, we provide a comprehensive study of mixed-valence coordination polymers from an analysis of the charge transport mechanism to their implementation as hole-conducting layers. CuII dithiocarbamate complexes afford morphology control of 1D polymer chains linked by (CuI2X2) copper halide rhombi. Concerted theoretical and experimental efforts identified the charge transport mechanism in the transition to band-like transport with a modeled effective hole mass of 6me. The iodide-bridged coordination polymer showed an excellent conductivity of 1 mS cm−1 and a hole mobility of 5.8 10−4 cm2 (V s)−1 at room temperature. Nanosecond selective hole injection into coordination polymer thin films was captured by nanosecond photoluminescence of halide perovskite films. Coordination polymers constitute a sustainable, tunable alternative to the current standard of heavily doped organic hole conductors.
Wang X, Li Z, Kavanagh S, et al., 2022, Lone pair driven anisotropy in antimony chalcogenide semiconductors, Physical Chemistry Chemical Physics, Vol: 2022, ISSN: 1463-9076
Antimony sulfide (Sb2S3) and selenide (Sb2Se3) have emerged as promising earth-abundant alternatives among thin-film photovoltaic compounds. A distinguishing feature of these materials is their anisotropic crystal structures, which are composed of quasi-one-dimensional (1D) [Sb4X6]n ribbons. The interaction between ribbons has been reported to be van der Waals (vdW) in nature and Sb2X3 are thus commonly classified in the literature as 1D semiconductors. However, based on first-principles calculations, here we show that inter-ribbon interactions are present in Sb2X3 beyond the vdW regime. The origin of the anisotropic structures is related to the stereochemical activity of the Sb 5s lone pair according to electronic structure analysis. The impacts of structural anisotropy on the electronic, dielectric and optical properties relevant to solar cells are further examined, including the presence of higher dimensional Fermi surfaces for charge carrier transport. Our study provides guidelines for optimising the performance of Sb2X3-based photovoltaics via device structuring based on the underlying crystal anisotropy.
Wang S, Huang M, Wu Y-N, et al., 2022, Effective Lifetime of Non-Equilibrium Carriers in Semiconductors from Non-Adiabatic Molecular Dynamics Simulations
<jats:title>Abstract</jats:title> <jats:p>The lifetime of non-equilibrium electrons and holes in semiconductors is crucial for solar cell and optoelectronic applications. Non-adiabatic molecular dynamics (NAMD) simulations based on time-dependent density functional theory (TDDFT) are widely used to study excited-state carrier dynamics. However, the calculated carrier lifetimes are often different from experimental results by orders of magnitude. In this work, by revisiting the definition of carrier lifetime and considering different recombination mechanisms, we report a systematic procedure for calculating the effective carrier lifetime in realistic semiconductor crystals that can be compared directly to experimental measurements. The procedure shows that considering all recombination mechanisms and using reasonable densities of carriers and defects are crucial in calculating the effective lifetime. When NAMD simulations consider only Shockey-Read-Hall (SRH) defect-assisted and band-to-band non-radiative recombination while neglect band-to-band radiative recombination, and the densities of non-equilibrium carriers and defects in supercell simulations are much higher than those in realistic semiconductors under solar illumination, the calculated lifetimes are ineffective and thus differ from experiments. Using our procedure, the calculated effective lifetime of the halide perovskite CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbI<jats:sub>3</jats:sub> agrees with experiments. It is mainly determined by band-to-band radiative and defect-assisted non-radiative recombination, while band-to-band non-radiative recombination is negligible. These results indicate that it is possible to calculate carrier lifetimes accurately based on NAMD simulations, but the directly calculated values should be converted to effective lifetimes for comparison to experiments. The revised procedure can be widely applied in future
Wang Y, Kavanagh SR, Burgues-Ceballos I, et al., 2022, Cation disorder engineering yields AgBiS<sub>2</sub> nanocrystals with enhanced optical absorption for efficient ultrathin solar cells, NATURE PHOTONICS, Vol: 16, Pages: 235-+, ISSN: 1749-4885
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- Citations: 68
Kim C-E, Lee J, Walsh A, et al., 2022, Role of ripples in altering the electronic and chemical properties of graphene, Journal of Chemical Physics, Vol: 156, Pages: 1-6, ISSN: 0021-9606
Ripples of graphene are known to manipulate electronic and hydrogenation properties of graphitic materials. More detailed work is needed to elucidate the structure–property relationship of these systems. In this work, the density functional theory is used to compute the energy and electronic structure of the graphene models with respect to variable curvatures and hydrogen adsorption sites. The magnitude of finite bandgap opening depends on the orientation of ripples, and the hydrogen adsorption energy depends on the local curvature of graphene. An adsorbed hydrogen alters the local curvature, resulting in relatively weakened adsorption on the neighboring three sites, which gives a rationale to experimentally observed dynamic equilibrium stoichiometry (H:C = 1:4) of hydrogenated graphene. The surface diffusion transition state energy of adsorbed hydrogen is computed, which suggests that the Eley–Rideal surface recombination mechanism may be important to establish the dynamic equilibrium, instead of the commonly assumed Langmuir–Hinshelwood mechanism.
Krenzer G, Kim C-E, Tolborg K, et al., 2022, Anharmonic lattice dynamics of superionic lithium nitride, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 10, Pages: 2295-2304, ISSN: 2050-7488
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- Citations: 8
Morgan LM, Islam MM, Yang H, et al., 2022, From Atoms to Cells: Multiscale Modeling of a LiNi<i><sub>x</sub></i>Mn<i><sub>y</sub></i>Co<i><sub>z</sub></i>O<sub>2</sub> Cathodes for Li-Ion Batteries, ACS ENERGY LETTERS, Vol: 7, Pages: 108-122, ISSN: 2380-8195
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- Citations: 10
Morita K, Davies D, Butler K, et al., 2022, Breaking the aristotype: featurisation of polyhedral distortions in perovskite crystals, Chemistry of Materials, Vol: 34, ISSN: 0897-4756
While traditional crystallographic representations of structure play an important role in materials science, they are unsuitable for efficient machine learning. A range of effective numerical descriptors have been developed for molecular and crystal structures. We are interested in a special case, where distortions emerge relative to an ideal high symmetry parent structure. We demonstrate that irreducible representations form anefficient basis for the featurisation of polyhedral deformations with respect to such an aristotype. Applied to a dataset of 552 octahedra in ABO3 perovskite-type materials, we use unsupervised machine learning with irreducible representation descriptors to identify four distinct classes of behaviour, associated with predominately corner, edge, face, and mixed connectivity between neighbouring octahedral units. Through this analysis, we identify SrCrO3 as a material with tuneable multiferroic behaviour. We further show, through supervised machine learning, that thermally activated structural distortions of CsPbI3 are well described by this approach.
Morgan LM, Mercer MP, Bhandari A, et al., 2022, Pushing the boundaries of lithium battery research with atomistic modelling on different scales, Progress in Energy, Vol: 4
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.
Doherty TAS, Nagane S, Kubicki DJ, et al., 2021, Stabilized tilted-octahedra halide perovskites inhibit local formation of performance-limiting phases, SCIENCE, Vol: 374, Pages: 1598-+, ISSN: 0036-8075
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- Citations: 78
Hou Q, Buckeridge J, Walsh A, et al., 2021, The Interplay of Interstitial and Substitutional Copper in Zinc Oxide, FRONTIERS IN CHEMISTRY, Vol: 9, ISSN: 2296-2646
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- Citations: 2
Walsh A, 2021, Atomistic models of metal halide perovskites, MATTER, Vol: 4, Pages: 3867-3873, ISSN: 2590-2393
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- Citations: 5
Rondiya SR, Jagt RA, MacManus-Driscoll JL, et al., 2021, Self-trapping in bismuth-based semiconductors: opportunities and challenges from optoelectronic devices to quantum technologies, Applied Physics Letters, Vol: 119, ISSN: 0003-6951
Semiconductors based on bismuth halides have gained attention for a wide range of electronic applications, including photovoltaics, light-emitting diodes, and radiation detectors. Their appeal is due to their low toxicity, high environmental stability under ambient conditions, and easy processability by a wide range of scalable methods. The performance of Bi-based semiconductors is dictated by electron–phonon interactions, which limit carrier mobilities and can also influence optoelectronic performance, for example, by giving rise to a large Stokes shift for photoluminescence, unavoidable energy loss channels, or shallow optical absorption onsets. In this Perspective, we discuss the recent understanding of how polarons and self-trapped excitons/carriers form in Bi-based semiconductors (particularly for the case of Cs2AgBiBr6), their impact on the optoelectronic properties of the materials, and the consequences on device performance. Finally, we discuss the opportunities that control of electron–phonon coupling enables, including stable solid-state white lighting, and the possibilities of exploiting the strong coupling found in bipolarons for quantum technologies.
Yang J-M, Jung Y-K, Lee J-H, et 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
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- Citations: 11
Krajewska CJ, Kavanagh SR, Zhang L, et 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
Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3Bi2Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3Bi2Br9 leads to substitution of up to 7% of the Bi(III) ions by equal quantities of Sn(II) and Sn(IV). The nature of the substitutional defects was studied by X-ray diffraction, 133Cs and 119Sn solid state NMR, X-ray photoelectron spectroscopy and density functional theory calculations. The resulting mixed-valence compounds show intense visible and near infrared absorption due to intervalence charge transfer, as well as electronic transitions to and from localised Sn-based states within the band gap. Sn(II) and Sn(IV) defects preferentially occupy neighbouring B-cation sites, forming a double-substitution complex. Unusually for a Sn(II) compound, the material shows minimal changes in optical and structural properties after 12 months storage in air. Our calculations suggest the stabilisation of Sn(II) within the double substitution complex contributes to this unusual stability. These results expand upon research on inorganic mixed-valent halides to a new, layered structure, and offer insights into the tuning, doping mechanisms, and structure–property relationships of lead-free vacancy-ordered perovskite structures.
Kavanagh SR, Savory CN, Scanlon DO, et al., 2021, Hidden spontaneous polarisation in the chalcohalide photovoltaic absorber Sn<sub>2</sub>SbS<sub>2</sub>I<sub>3</sub>, MATERIALS HORIZONS, Vol: 8, ISSN: 2051-6347
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- Citations: 19
Bibi A, Lee I, Nah Y, et al., 2021, Lead-free halide double perovskites: Toward stable and sustainable optoelectronic devices, MATERIALS TODAY, Vol: 49, Pages: 123-144, ISSN: 1369-7021
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- Citations: 36
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
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- Citations: 9
Huang Y-T, Kavanagh SR, Scanlon DO, et al., 2021, Perovskite-inspired materials for photovoltaics and beyond-from design to devices (vol 32, 132004, 2021), NANOTECHNOLOGY, Vol: 32, ISSN: 0957-4484
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- Citations: 2
Krenzer G, Kim C-E, Tolborg K, et al., 2021, Anharmonic lattice dynamics of superionic lithium nitride
<jats:p>Superionic crystals reach an ionic conductivity comparable to liquid electrolytes following a superionic transition at high temperature. The physical mechanisms that lead to this behaviour remain poorly understood. It has been proposed that superionic transitions are accompanied by the breakdown of specific phonon modes linked to characteristic diffusion processes. Any changes in vibrational properties across the superionic transition may therefore provide insights into the underlying physics of this phenomenon. Here, we apply a combination of lattice dynamics and ab initio molecular dynamics to probe the vibrational properties of the archetypal superionic conductor Li3N. We assess harmonic, quasi-harmonic, and anharmonic descriptions of the phonons. The harmonic and quasi-harmonic models show no change in features across the superionic transition. The fully anharmonic model, however, exhibits a phonon breakdown for all modes above the superionic transition temperature. The implications for developing lattice-dynamics based descriptors for superionic conductors are discussed.</jats:p>
Krenzer G, Kim C-E, Tolborg K, et al., 2021, Anharmonic lattice dynamics of superionic lithium nitride
<jats:p>Superionic crystals reach an ionic conductivity comparable to liquid electrolytes following a superionic transition at high temperature. The physical mechanisms that lead to this behaviour remain poorly understood. It has been proposed that superionic transitions are accompanied by the breakdown of specific phonon modes linked to characteristic diffusion processes. Any changes in vibrational properties across the superionic transition may therefore provide insights into the underlying physics of this phenomenon. Here, we apply a combination of lattice dynamics and ab initio molecular dynamics to probe the vibrational properties of the archetypal superionic conductor Li3N. We assess harmonic, quasi-harmonic, and anharmonic descriptions of the phonons. The harmonic and quasi-harmonic models show no change in features across the superionic transition. The fully anharmonic model, however, exhibits a phonon breakdown for all modes above the superionic transition temperature. The implications for developing lattice-dynamics based descriptors for superionic conductors are discussed.</jats:p>
Jung Y-K, Kim S, Kim YC, et al., 2021, Low Barrier for Exciton Self-Trapping Enables High Photoluminescence Quantum Yield in Cs<sub>3</sub>Cu<sub>2</sub>I<sub>5</sub>, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 12, Pages: 8447-8452, ISSN: 1948-7185
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- Citations: 13
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