The organic-inorganic hybrid perovskite CH3NH3PbI3 has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical ...The organic-inorganic hybrid perovskite CH3NH3PbI3 has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical stability is one major challenge in the development of CH3NH3PbI3 solar cells. It was commonly assumed that moisture or oxygen in the environment causes the poor stability of hybrid halide perovskites, however, here we show from the first-principles calculations that the room-temperature tetragonal phase of CH3NH3PbI3 is thermodynamically unstable with respect to the phase separation into CH3NH3I ＋ PbI2, i.e., the disproportionation is exothermic, independent of the humidity or oxygen in the atmosphere. When the structure is distorted to the low-temperature orthorhombie phase, the energetic cost of separation increases, but remains small. Contributions from vibrational and configurational entropy at room temperature have been considered, but the instability of CH3NH3PbI3 is unchanged. When I is replaced by Br or CI, Pb by Sn, or the organic cation CH3NH3 by inorganic Cs, the perovskites become more stable and do not phase-separate spontaneously. Our study highlights that the poor chemical stability is intrinsic to CH3NH3PbI3 and suggests that element-substitution may solve the chemical stability problem in hybrid halide perovskite solar cells.展开更多
Perovskite is an important material type in geophysics and for technologically important applications.However,the number of synthetic perovskites remains relatively small.To accelerate the high-throughput discovery of...Perovskite is an important material type in geophysics and for technologically important applications.However,the number of synthetic perovskites remains relatively small.To accelerate the high-throughput discovery of perovskites,we propose a graph neural network model to assess their synthesizability.Our trained model shows a promising 0.957 out-of-sample true positive rate,significantly improving over empirical rule-based methods.Further validation is established by demonstrating that a significant portion of the virtual crystals that are predicted to be synthesizable have already been indeed synthesized in literature,and those with the lowest synthesizability scores have not been reported.While previous empirical strategies are mainly applicable to metal oxides,our model is general and capable of predicting the synthesizability across all classes of perovskites,including chalcogenide,halide,and hydride perovskites,as well as anti-perovskites.We apply the method to identify synthesizable perovskite candidates for two potential applications,the Li-rich ion conductors and metal halide optical materials that can be tested experimentally.展开更多
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 Cs_(3)Cu_(2)I_(5),which has a crystal structure...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 Cs_(3)Cu_(2)I_(5),which has a crystal structure formed of zero-dimensional[Cu_(2)I_(5)]3−anionic clusters that are separated by Cs+counter cations.We find the compound exhibits the characteristics of a phonon-glass electroncrystal 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(<0.1Wm^(−1)K^(−1)).The dispersive conduction band leads to a high electron mobility(>10 cm^(2)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%.展开更多
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 tr...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 undermechanical 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.The formation energy of the carrier generating defects increased in convex bending environments clarifying the degradation of the surface current.Moreover,alkali-related defects had lower formation energy than the intrinsic acceptors,mitigating current degradation in mechanical stress condition.The altered defect energy levels were attributed to the deformation of the crystal structure under bending states.This study provides insights into the mitigating of strain-induced charge degradation for enhancing the performance and robustness of flexible CIGS photovoltaic devices.展开更多
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...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.To address this issue,we report an approach to navigate the defect configurational landscape using targeted bond distortions and rattling.Application of our workflow to eight materials(CdTe,GaAs,Sb_(2)S_(3),Sb_(2)Se_(3),CeO_(2),In_(2)O_(3),ZnO,anatase-TiO_(2))reveals symmetry breaking in each host crystal that is not found via conventional local minimisation techniques.The point defect distortions are classified by the associated physico-chemical factors.We demonstrate the impact of these defect distortions on derived properties,including formation energies,concentrations and charge transition levels.Our work presents a step forward for quantitative modelling of imperfect solids.展开更多
While the theory of imperfections in solids is firmly established,procedures for first-principles calculations of defect quantities continue to evolve.A plethora of ad hoc correction schemes is being replaced by sophi...While the theory of imperfections in solids is firmly established,procedures for first-principles calculations of defect quantities continue to evolve.A plethora of ad hoc correction schemes is being replaced by sophisticated self-consistent procedures that will enable more quantitative predictions of the formation energies of defect species and their spectroscopic signatures.展开更多
Defects dictate the properties of many functional materials.To understand the behaviour of defects and their impact on physical properties,it is necessary to identify themost stabledefect geometries.However,global str...Defects dictate the properties of many functional materials.To understand the behaviour of defects and their impact on physical properties,it is necessary to identify themost stabledefect geometries.However,global structure searching is computationally challenging for high-throughput defect studies ormaterials with complex defect landscapes,like alloys or disordered solids.Here,we tackle this limitation by harnessing a machine-learning surrogate model to qualitatively explore the structural landscape of neutral point defects.展开更多
基金supported by the Special Funds for Major State Basic ResearchNational Natural Science Foundation of China(NSFC)+6 种基金Project of Shanghai Municipality(16520721600)supported by NSFC under Grant No 91233121Shanghai Rising-Star Program(14QA1401500)CC of ECNUsupported by the Royal Society,the ERC and EPSRC under Grant Nos EP/M009580/1 and EP/K016288/1supported by the National Key Research and Development Program of China under Grant No 2016YFB0700700the National Natural Science Foundation of China under Grant Nos 51672023,11634003 and U1530401
文摘The organic-inorganic hybrid perovskite CH3NH3PbI3 has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical stability is one major challenge in the development of CH3NH3PbI3 solar cells. It was commonly assumed that moisture or oxygen in the environment causes the poor stability of hybrid halide perovskites, however, here we show from the first-principles calculations that the room-temperature tetragonal phase of CH3NH3PbI3 is thermodynamically unstable with respect to the phase separation into CH3NH3I ＋ PbI2, i.e., the disproportionation is exothermic, independent of the humidity or oxygen in the atmosphere. When the structure is distorted to the low-temperature orthorhombie phase, the energetic cost of separation increases, but remains small. Contributions from vibrational and configurational entropy at room temperature have been considered, but the instability of CH3NH3PbI3 is unchanged. When I is replaced by Br or CI, Pb by Sn, or the organic cation CH3NH3 by inorganic Cs, the perovskites become more stable and do not phase-separate spontaneously. Our study highlights that the poor chemical stability is intrinsic to CH3NH3PbI3 and suggests that element-substitution may solve the chemical stability problem in hybrid halide perovskite solar cells.
基金We acknowledge generous financial support from NRF Korea(NRF-2019M3D3A1A01069099).
文摘Perovskite is an important material type in geophysics and for technologically important applications.However,the number of synthetic perovskites remains relatively small.To accelerate the high-throughput discovery of perovskites,we propose a graph neural network model to assess their synthesizability.Our trained model shows a promising 0.957 out-of-sample true positive rate,significantly improving over empirical rule-based methods.Further validation is established by demonstrating that a significant portion of the virtual crystals that are predicted to be synthesizable have already been indeed synthesized in literature,and those with the lowest synthesizability scores have not been reported.While previous empirical strategies are mainly applicable to metal oxides,our model is general and capable of predicting the synthesizability across all classes of perovskites,including chalcogenide,halide,and hydride perovskites,as well as anti-perovskites.We apply the method to identify synthesizable perovskite candidates for two potential applications,the Li-rich ion conductors and metal halide optical materials that can be tested experimentally.
基金We thank J.M.Skelton and A.M.Ganose for useful discussions on phonon and electron transport.Via our membership of the UK’s HEC Materials Chemistry Consortium,which is funded by EPSRC(EP/L000202)this work used the ARCHER UK National Supercomputing Service(http://www.archer.ac.uk).This work was supported by a National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.2018R1C1B6008728)This research was partially supported by the Graduate School of YONSEI University Research Scholarship Grants in 2019.
文摘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 Cs_(3)Cu_(2)I_(5),which has a crystal structure formed of zero-dimensional[Cu_(2)I_(5)]3−anionic clusters that are separated by Cs+counter cations.We find the compound exhibits the characteristics of a phonon-glass electroncrystal 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(<0.1Wm^(−1)K^(−1)).The dispersive conduction band leads to a high electron mobility(>10 cm^(2)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%.
基金supported by national R&D programs through the National Research Foundation of Korea(grant number:RS-2024-00355905,NRF-2018R1A6A1A03025340,NRF-2022M3J1A1064229)funded by the Ministry of Education and the Ministry of Science and ICT,and the framework of the Research and Development Program of the Korea Institute of Energy Research(grant number:C4-2412).
文摘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 undermechanical 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.The formation energy of the carrier generating defects increased in convex bending environments clarifying the degradation of the surface current.Moreover,alkali-related defects had lower formation energy than the intrinsic acceptors,mitigating current degradation in mechanical stress condition.The altered defect energy levels were attributed to the deformation of the crystal structure under bending states.This study provides insights into the mitigating of strain-induced charge degradation for enhancing the performance and robustness of flexible CIGS photovoltaic devices.
基金I.M.L.thanks La Caixa Foundation for funding a postgraduate scholarship(ID 100010434,fellowship code LCF/BQ/EU20/11810070)S.R.K.acknowledges the EPSRC Centre for Doctoral Training in the Advanced Characterisation of Materials(CDT-ACM)(EP/S023259/1)for funding a PhD studentship+2 种基金DOS acknowledges support from the EPSRC(EP/N01572X/1)and from the European Research Council,ERC(Grant No.758345)Via membership of the UK’s HEC Materials Chemistry Consortium,which is funded by the EPSRC(EP/L000202,EP/R029431,EP/T022213)this work used the UK Materials and Molecular Modelling(MMM)Hub(Thomas EP/P020194 and Young EP/T022213).
文摘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.To address this issue,we report an approach to navigate the defect configurational landscape using targeted bond distortions and rattling.Application of our workflow to eight materials(CdTe,GaAs,Sb_(2)S_(3),Sb_(2)Se_(3),CeO_(2),In_(2)O_(3),ZnO,anatase-TiO_(2))reveals symmetry breaking in each host crystal that is not found via conventional local minimisation techniques.The point defect distortions are classified by the associated physico-chemical factors.We demonstrate the impact of these defect distortions on derived properties,including formation energies,concentrations and charge transition levels.Our work presents a step forward for quantitative modelling of imperfect solids.
基金Support was received from the Faraday Institution(faraday.ac.uk,EP/S003053/1),grant No.FIRG025.
文摘While the theory of imperfections in solids is firmly established,procedures for first-principles calculations of defect quantities continue to evolve.A plethora of ad hoc correction schemes is being replaced by sophisticated self-consistent procedures that will enable more quantitative predictions of the formation energies of defect species and their spectroscopic signatures.
基金S.R.K.acknowledges the EPSRC Centre for Doctoral Training in the Advanced Characterisation of Materials(CDT-ACM)(EP/S023259/1)for funding a PhD studentshipA.M.G.is supported by EPSRC Fellowship EP/T033231/1+2 种基金A.W.is supported by EPSRC project EP/X037754/1We are grateful to the UK Materials and Molecular Modelling Hub for computational resources,which are partially funded by EPSRC(EP/P020194/1 and EP/T022213/1)This work used the ARCHER2 UK National Supercomputing Service(https://www.archer2.ac.uk)via our membership of the UK’s HEC Materials Chemistry Consortium,which is funded by EPSRC(EP/L000202).
文摘Defects dictate the properties of many functional materials.To understand the behaviour of defects and their impact on physical properties,it is necessary to identify themost stabledefect geometries.However,global structure searching is computationally challenging for high-throughput defect studies ormaterials with complex defect landscapes,like alloys or disordered solids.Here,we tackle this limitation by harnessing a machine-learning surrogate model to qualitatively explore the structural landscape of neutral point defects.
