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Recent advances in controlling the crystallization of two-dimensional perovskites for optoelectronic device

Frontiers of physics 2019年第5期14卷 1-17页

作者： Shi-Qiang Luo Ji-Fei Wang Bin Yang Yong-Bo Yuan Hunan Key Laboratory of Super Micro structure and Ultrafast Process School of Physics and ElectronicsCentral South UniversityChangsha 410083China College of Physic and Electric Information Hunan Institute of Science and TechenologyYueyang 414006China College of Materials Science and Engineering Hunan UniversityChangsha 410082China Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology Hunan UniversityChangsha 410082China

Though three-dimensional (3D) organic inorganic halide perovskites (OIHP) is very promising for low cost and distributed PV generation,the stability issue of 3D OIHP is still a problem for its ***-dimensional (2D) perovskites,protected by periodic organic ligands,is promising due to its excellent optoelectronic property and superior ***,2D perovskitc is anisotropic in its crystal structure and optoelectronic properties,and the resulted film is often a mixture of different ***,methods to manipulate 2D perovskitc crystal orientation and its phase separation are *** this review,the major advances on the composition engineering,crystal orientation,phase separa-tion,and inlerfaeial capping are ***,efforts on understanding the formation process of 2D perovskitc crystal arc also discussed,which is important for making full use of 2D perovskitc in functional optoelectronic devices.

关键词： optoelectronic devices perovskite solar cells nanoscale materials chemical vapor deposition

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Intrinsically ultralow lattice thermal conductivity and giant thermoelectric effect in Ag-based intercalated layered crystalline solids

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Physical Review B 2024年第23期109卷 235202-235202页

作者： Junpeng Yuan Min Li Hui Wang School of Physics Hunan Key Laboratory of Super Microstructure and Ultrafast Process Hunan Key Laboratory of Nanophotonics and Devices State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China

Understanding the nature of low thermal conductivity and phonon transport properties is critical for the design of potential thermoelectric materials. Based on density-functional theory combined with the phonon Peierls-Boltzmann transport equation, we reveal that Ag-based intercalated layered materials AgBiX2 (X = S, Se, and Te) have inherently low lattice thermal conductivity, which is mainly attributed to the anticrossing behavior of low-frequency optical phonons and longitudinal acoustic phonons induced by the rattling mode of the cations. It is found that the optical phonons in AgBiS2 contribute dominantly (up to 65%) to the total thermal conductivity, originating from the weak bonding nature of intercalated Ag atoms that leads to strong anharmonicity and softening of transverse acoustic phonons. Electronic relaxation times under acoustic deformation potential scattering, polar optical phonon scattering, and ionized impurity scattering are considered to obtain reasonable electron transport properties. The ZT value of p-type AgBiS2 reaches 1.77 for optimal doping at room temperature, which can further be enhanced to ∼2.6 through strain engineering. The present work demonstrates that chemically controlled weak bonding in Ag-based intercalated layered structure produces intrinsically low thermal conductivity and provides important theoretical insight for thermal insulator and thermoelectric applications.

关键词： Anharmonic lattice dynamics Electrical conductivity Electron-phonon coupling Electronic structure Phonons Scattering theory Seebeck effect Thermal conductivity Thermoelectric effects Thermoelectrics 3-dimensional systems Layered crystals Ab initio molecular dynamics Boltzmann theory Density functional calculations Density functional theory First-principles calculations

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Quenching Induced Fracturing and Self-rolling of Monolayer CVDgrown MoS2

Quenching Induced Fracturing and Self-rolling of Monolayer C...

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2017第六届国际新材料大会

作者： Han Huang Hunan Key Laboratory for Super-microstructure and Ultrafast Process Central South University China

Fracture is a widely presented phenomenon in nature from macro-to micro-scopic scale,even to atomical *** contrast to the case for three dimensional materials,research on the fracture properties of two dimension（2 D） materials is *** this lecture,I will give a talk about the novel thermal tensile strain-induced transgranular fracturing of monolayer MoS single-crystalline microflakes due to the fast cooling during CVD *** Raman and Photoluminescence results reveal the lattice-shrink-induced compressive rather than tensile strain in the fractured M0 S2 microflakes,which enlarges the corresponding band gap by65 *** compressive strain induces the fractured MoS to self-roll from the edges into *** findings deepen the understanding of fracture behaviors of monolayer single-crystalline MoS and demonstrate a promising method to engineer the strain in MoS-like atomically thin materials to further tune their physical properties.

关键词： Quenching Induced Fracturing and Self-rolling of Monolayer CVDgrown MoS2

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Enhanced thermodynamic stability and carrier lifetime in BF4-doped wide-band-gap perovskite solar cells

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Physical Review B 2024年第4期110卷 045142-045142页

作者： Zhong-Yuan Wang Kai-Feng Wang Jun-Jie Jin Fangping Ouyang Biao Meng Zhaofeng Wu Li-Min Liu Chuan-Jia Tong Institute of Quantum Physics Hunan Key Laboratory of Nanophotonics and Devices Hunan Key Laboratory of Super-Microstructure and Ultrafast Process School of Physics School of Material Science and Engineering School of Physics

Recent experiments show that doping a small amount of fluorinated pseudohalides (BF4) into CH3NH3PbI3 (MAPbI3) can enhance the performance of wide-band-gap (WBG) perovskite solar cells. Using time-domain density functional theory and ab initio nonadiabatic molecular dynamics we demonstrate that BF4-doped WBG perovskites not only maintain the high defect tolerance but also exhibit greatly improved thermodynamic stability due to enhanced dissociation energy and reduced thermal atomic fluctuation. The strengthened hydrogen bond network introduces increased lattice rigidity, confined inner space, and the reorientated dipole direction of methylammonium molecules, which synergistically suppress the ion migration in BF4-doped MAPbI3 perovskite. Notably, the charge carrier lifetime experiences an order-of-magnitude improvement after BF4 doping, which is mainly attributed to the weakened nonadiabatic coupling. This work provides valuable insights into the effect of fluorinated pseudohalides doped in perovskite materials and suggests a promising approach to enhancing the stability and efficiency of WBG perovskite solar cells.

关键词： Carrier dynamics Electron-phonon coupling Organic-inorganic hybrid perovskites Photovoltaic absorbers Density functional calculations Molecular dynamics

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Giant reversible electrocaloric effect in monolayer group-IV monochalcogenides

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Physical Review B 2024年第6期110卷 064103页

作者： Xiong Xu Min Li X. Lin Hui Wang School of Physics Hunan Key Laboratory of Super Microstructure and Ultrafast Process Hunan Key Laboratory of Nanophotonics and Devices State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China

Monolayer electrocaloric (EC) materials have emerged as promising candidates to achieve economic and green solid-state refrigeration, especially in micro- or nanoscale chip cooling in the post-Moore law period. In this paper, we trained a machine-learning-based deep potential (DP) model of monolayer group-IV monochalcogenides MXs (M = Ge, Sn; X = S, Se) with a database from first-principles calculations, which incorporates the accuracy of ab initio molecular dynamics and efficiency of classical method. The DP model was further applied to study the EC effect (ECE) in monolayer MXs by simulating the temperature-driven phase transitions and electric polarization dynamics under different external electric fields. The results indicate MXs featuring giant reversible isothermal entropy change (ΔS) and adiabatic temperature change (ΔT) near their order-disorder phase transition. Particularly, for E = 100 MV/m, |ΔS| = 68 J/(kg K) and |ΔT| = 75 K are obtained for GeS, which individually rival the state-of-the-art ECE figures of merit, surpassing most other ferroelectric materials, particularly the two-dimensional (2D) CuInPS and strained SrTiO3 films. Furthermore, electric field shifts of the order of 10 MV/m yield huge reversible EC strengths of ΔS/ΔE = 5.4 Jmkg−1K−1MV−1 and ΔT/ΔE = 6 KmMV−1. The origin of the giant ECE in MXs was explained through macroscopic thermodynamic ratios, phenomenological Landau theory, and microscopic phonon vibration analysis. Interestingly, the entropy change can be approximated to be proportional to the square of the polarization change (ΔP2), and the application of electric field shifts the low-frequency phonons to the higher-frequency range, with the M atom contributing more to the entropy change than the X atom. In this paper, we provide important insights for exploration and design of 2D EC materials in future practical applications.

关键词： Electrocaloric effect Entropy Solid-state refrigeration 2-dimensional systems Ferroelectrics Ab initio molecular dynamics Machine learning

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Vacuum deposited film growth,morphology and interfacial electronic structures of 2,7-dioctylbenzothieno[3,2-b]benzothiophene(C8-BTBT)

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Journal of Central South University 2022年第4期29卷 1041-1061页

作者： WEI Jun-hua NIU Dong-mei GAO Yong-li Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and ElectronicsCentral South UniversityChangsha 410083China Department of Physics and Astronomy University of RochesterRochesterNY 14627USA

Interfaces play critical roles in electronic devices and provide great diversity of film morphology and device *** retrospect the substrate mediated vacuum film growth of benchmark high mobility material 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene(C8-BTBT)and the interface electronic *** film growth of C8-BTBT molecules is diversified depending on the substrate-molecule and molecule-molecule *** atomic smooth substrates C8-BTBT film grows in layer-by-layer mode while on coarse substrate it grows in islands *** initial molecular layer at dielectric,semiconductor and conductive substrates displays slight different lattice *** initial molecule orientation depends on the substrate and will gradually change to standing up configuration as in bulk phase.C8-BTBT behaves as electron donor when contacting with dielectric and stable conductive *** usually induces a dipole layer pointing to C8-BTBT and an upward bend bending in C8-BTBT side toward the *** it is air stable,C8-BTBT is chemically reactive with some transition metals and *** orientation change from lying down to standing up in the film usually leads to decrease of ionization *** article provides insights to the interface physical and chemical processes and suggestions for optimal design and fabrication of C8-BTBT based devices.

关键词： interface film morphology packing configuration growth mode electronic structure chemical reaction interface dipole

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High thermoelectric performance induced by strong anharmonicity in ternary Li-based chalcogenides

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Physical Review B 2024年第15期110卷 155202页

作者： Linyuan Cheng Min Li Long Zhang Hui Wang School of Physics Hunan Key Laboratory of Super Microstructure and Ultrafast Process Hunan Key Laboratory of Nanophotonics and Devices State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China

Thermoelectric materials enable heat-to-electricity conversion, while its efficiency has so far been restricted by the dimensionless figure of merit (ZT). In this study, we employ first-principles calculations combined with Boltzmann transport equation along with the thermal transport unified theory to investigate the electrical and thermal transport properties of a family of Li-based chalcogenides (Li3BX4, B=V, Nb, Ta and X=S, Se, Te). It is found that Li3BTe4 exhibit ultralow lattice thermal conductivity (κL) at room temperature, as lows as ∼0.1 W/mK. This is mainly attributed to the relatively weak interaction between the B and Te atom as confirmed by the small number of bonding states below the Fermi level, which introduces strong anharmonicity and significantly enhances the phonon scattering rate. Moreover, the observed power factors of Li3BTe4 are more than 10 µWcm−1K−2 at 300 K, giving rise to giant ZT at intermediate and high temperatures in both p-type and n-type, for instance, ZT reaches 2.25 ∼ 2.46 in Li3NbTe4 even after considering both particlelike propagation and wavelike phonon tunneling transport mechanism. In addition, we find that ZT of Li3BX4 can further be enhanced through moderate strain engineering and these Li-based chalcogenides exhibit high ductility which is favorable for the post machining process. The present work unravels the importance of strong anharmonicity induced by weak-bonded heavy element on the thermoelectric performance in Li3BX4 family which provides important insights for the rational design of flexible thermoelectric devices.

关键词： Anharmonic lattice dynamics Electron-phonon coupling Electronic structure Phonons Scattering theory Seebeck effect Thermal conductivity Thermoelectric effects Thermoelectrics 3-dimensional systems Chalcogenides Ab initio molecular dynamics Boltzmann theory Density functional calculations Density functional theory First-principles calculations

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Room-temperature ferromagnetism and half-metallicity in monolayer orthorhombic CrS_(2)

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Frontiers of physics 2024年第4期19卷 137-146页

作者：雷博程李奥林周文哲王云鹏熊威陈羽欧阳方平 School of Physics Science and Technology and Xinjiang Key Laboratory of Solid-State Physics and DevicesXinjiang UniversityUrumqi 830046China School of Physics and Hunan Key Laboratory for Super-Microstructure and Ultrafast Processand Hunan Key Laboratory of Nanophotonics and DevicesCentral South UniversityChangsha 410083China School of Physics Science and Technology and Xinjiang Laboratory of Phase Transitions and Microstructures in Condensed Matter PhysicsYili Normal UniversityYining 835000China Powder Metallurgy Research Institute and State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China

Two-dimensional materials with high-temperature ferromagnetism and half-metallicity have the latest applications in spintronic *** on first-principles calculations,we have investigated a novel two-dimensional CrS_(2) phase with an orthorhombic *** results suggest that it is stable in dynamics,thermodynamics,and *** ground state of monolayer orthorhombic CrS_(2) is both ferromagnetic and half-metallic,with a high Curie temperature of 895 K and a large spin-flipping gap on values of 0.804 *** room-temperature ferromagnetism and halfmetallicity can maintain stability against a strong biaxial strain ranging from–5%to 5%.Meanwhile,increasing strain can significantly maintain the out-of-plane magnetic anisotropy.A density of states analysis,together with the orbital-resolved magnetic anisotropy energy,has revealed that the strain-enhanced MAE is highly related to the 3d-orbital splitting of Cr *** results suggest the monolayer orthorhombic CrS_(2) is an ideal candidate for future spintronics.

关键词： orthorhombic CrS_(2) Curie temperature magnetic anisotropy energy biaxial strain first-principles calculations

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Ablation enhancement by defocused irradiation assisted femtosecond laser fabrication of stainless alloy

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Chinese Optics Letters 2018年第1期16卷 53-56页

作者：褚东凯银恺董欣然罗志宋雨欣段吉安 Hunan Key Laboratory of Super Microstructure and Ultrafast Process School of Physics and ElectronicsCentral South University The State Key Laboratory of High Performance Complex Manufacturing College of Mechanical and Electrical Engineering Central South University

We evaluate the effects of the holes geometry drilled by a femtosecond laser on a stainless alloy with various defocused irradiation time, which ranges from 0 min to 1 h. The laser ablation efficiency is increased by a factor of3 when the irradiation time is elevated from 0 to 30 min. Also, the morphology of the hole is observed by a scanning electron microscope, where the result indicates that the defocused irradiation time has a significant influence on the morphology changes. The reason for such changes is discussed based on the pretreatment effect and the confined plasma plume. As an application example, the microchannel is fabricated by a femtosecond laser combined with the defocused irradiation to demonstrate the advantage of the proposed method in fabricating functional structures.

关键词： Ablation enhancement by defocused irradiation assisted femtosecond laser fabrication of stainless alloy

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A first-principles study on zigzag phosphorene nanoribbons terminated by transition metal atoms

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Chinese Physics B 2021年第2期30卷 476-480页

作者： Shuai Yang Zhiyong Wang Xueqiong Dai Jianrong Xiao Mengqiu Long College of Science Guilin University of TechnologyGuilin 541008China Modern Education Technology Center Guilin University of TechnologyGuilin 541008China Hunan Key Laboratory of Super Micro-structure and Ultrafast Process Central South UniversityChangsha 410083China

We have investigated the electronic and magnetic properties of zigzag phosphorene nanoribbons(ZPNRs)with transition metal(TM)passivated atoms,it can be found that the ZPNRs with TM passivated atoms exhibit different magnetisms except for the Ni-passivated ***,the results show that the magnetic moments of ZPNRs with TM passivated atoms are larger than that of ZPNRs with other passivated non-metals/***,it can be found that Fe-passivated ZPNR exhibits magnetic semiconducting character,which provides the possbility for the application of phosphorene in information *** Mn-passivated ZPNRs,it exhibits the *** results may be useful for potential applications of phosphorene in electronic and high-performance spintronic devices.

关键词： phosphorene first-principles calculations half-metallicity passivated

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