有机铵盐表面稳定化CsPbI_2Br全无机钙钛矿

有机-无机杂化钙钛矿中的有机阳离子组分具有在光照和加热条件下本征的化学不稳定性,而全无机钙钛矿有望从根本上解决组分稳定性问题.但是,全无机钙钛矿在湿度条件下,极易相变为非光学活性的d相.本文以CsPbI_2Br全无机钙钛矿为对象,研究不同碳链长度的有机铵盐表面处理对于钙钛矿湿稳定性和器件光电性能的影响.实验结果表明,有机铵盐碳链的增长显著改善钙钛矿相稳定性.其中,当用碘化丁铵处理时, CsPbI_2Br全无机钙钛矿表现出最佳的湿稳定性.随着碘化丁铵的处理浓度的增加,钙钛矿的湿稳定性进一步改善.当用适宜浓度的碘化丁铵处理CsPbI_2Br薄膜时,钙钛矿层表层的丁铵阳离子对电荷传输不会有明显阻碍,可以获得优良的器件效率.总之,适宜的有机阳离子层既能提高全无机钙钛矿的湿稳定性,又能改善其光伏性能.     

有机-无机杂化卤化物钙钛矿材料稳定性及其在光电探测器方面的研究进展(特邀)

有机-无机杂化钙钛矿材料(CH_3NH_3PbX_3)因其具有载流子迁移率高、直接带隙结构、光电转换效率高等优异的光电性能,在太阳能电池、光电探测器、发光二极管及激光器等光电子领域具有重要应用前景。然而,有机-无机杂化钙钛矿材料的稳定性问题是现阶段限制其进一步应用的瓶颈。本文首先系统论述子外界环境因素(水氧、温度、光照等)对有机-无机杂化钙钛矿材料稳定性的影响因素与物理机制。其次,总结了目前改善及提高钙钛矿材料稳定性的主要方法和技术途径,如改进合成方法、离子掺杂、器件封装等手段。同时分析了其对基于有机-无机杂化钙钛矿材料光电探测器性能的影响。最后提出了该领域在实际应用中面临的挑战和发展策略。     

高压下有机-无机杂化钙钛矿CH_3NH_3PbI_3的结构及光学性质研究

近年来,随着有机-无机杂化钙钛矿太阳能电池的飞速发展,对此类材料基本物性的探索引起了科学家们的广泛关注.本文利用金刚石对顶砧装置对甲胺基碘化铅(CH_3NH_3PbI_3)进行高压实验,研究了室温下压力诱导CH_3NH_3PbI_3的结构变化以及压力对其光学性质的调控,实验最高压力为7 GPa.原位高压同步辐射X射线衍射实验结果显示,CH_3NH_3PbI_3样品在0.3 GPa由四方相转变为正交相,在4 GPa左右开始非晶化.结合原位高压吸收和荧光光谱,分析了压力对CH_3NH_3PbI_3带隙大小的调控作用.进一步利用原位高压拉曼光谱和红外光谱实验研究了CH_3NH_3PbI_3晶体中有机阳离子(CH_3NH_3~+)在高压下的行为.完全卸压后,样品恢复到加压前的初始状态.研究结果可为深入了解有机-无机杂化钙钛矿的光学性质和结构稳定性提供一些信息.     

有机-无机杂化钙钛矿自组装量子阱结构的能带调控和光电性能的研究

有机-无机杂化钙钛矿材料具有分子尺度上调节能带结构的特点,在光、电、磁等领域均表现出了优异的性能.通过简单的旋涂方法,成功的制备了具有不同无机层层数的杂化钙钛矿材料(C₆H₁₃NH₃)₂(CH₃NH₃)_n-1Pb_nI_3n+1 (简写为C₆Pb关键词： 杂化钙钛矿 量子阱 带隙 光电性能     

有机-无机杂化钙钛矿材料的本征稳定性

有机-无机杂化钙钛矿太阳能电池的光电转换效率已逾24%,效率的飞速提升加之可低成本溶液法制备的市场优势,使人们越来越期待钙钛矿太阳能电池的商业化.目前钙钛矿太阳能电池商业化所面临最大的障碍是材料乃至器件的长期不稳定性,这使其无法在使用寿命上与已商品化的硅基等太阳能电池匹敌.本文从化学不稳定性和相不稳定性两个层面剖析了有机-无机杂化钙钛矿材料本征不稳定性的问题,并从组分设计及制备工艺等角度给出了提高钙钛矿太阳能电池器件稳定性的相关建议.     

全无机钙钛矿太阳能电池湿度稳定性和光热稳定性研究进展

近年来,钙钛矿太阳能电池因高效率、低成本等特点获得了持续的关注,但是有机成分在稳定性方面始终存在一些问题。相比于有机-无机杂化钙钛矿太阳能电池,全无机钙钛矿材料可以很大程度上避免外界环境的影响,对氧环境要求低,对于湿度环境的容许度也比较大;由于自身结构,在光热稳定性方面,也要优于有机-无机杂化钙钛矿。因此,发展全无机钙钛矿太阳能电池是有效提高钙钛矿太阳能电池稳定性的方向之一。本文从稳定性方面入手,系统地介绍了全无机钙钛矿太阳能电池的最新研究进展。结合全无机钙钛矿太阳能电池稳定性的影响因素,总结了当前全无机钙钛矿电池稳定性问题的主要解决方案,最后对解决全无机钙钛矿材料的稳定性进行了展望。     

基于二维有机无机杂化钙钛矿的薄膜晶体管

三维有机无机杂化钙钛矿因其优异的光电性能被视为光电领域极具前景的材料,但其在湿度环境下的不稳定性成为制约产业化进程的关键因素之一.本文采用一步溶液法成功制备了碘化铅基二维钙钛矿(PEA)_2(MA)_(n–1)Pb_nI_(3n+1) (n=1, 3,6, 20, 30),对钙钛矿的维度及微观结构进行调控,并将其应用作为薄膜晶体管(TFTs)器件的半导体沟道层.实验结果表明,独特的二维层状结构和量子约束效应有效地抑制了器件的环境不稳定性和离子迁移现象, TFTs器件性能得到提高.基于准二维Quasi-2D (n=6)钙钛矿的薄膜晶体管器件空穴迁移率(μ_(hole))达到3.9 cm~2/(V·s)、阈值电压为1.85 V、开关比高于10~4.首次提出将准二维有机无机杂化钙钛矿材料应用到薄膜晶体管中,为制备高性能、高稳定性的薄膜晶体管器件提供了新的思路.     

高压下低维有机-无机杂化钙钛矿MAPbI3纳米立方块带隙调控及光学性能的研究

低维有机-无机杂化钙钛矿材料由于其独特的光电性能而受到广泛关注。本文利用金刚石对顶砧装置对不同尺寸的CH_3NH_3PbI_3(MAPbI_3)纳米立方块进行了高压研究。并探索了尺寸效应对MAPbI_3纳米立方块在高压下的光学性能的影响规律。高压原位紫外-可见吸收和荧光光谱结果显示,两种不同尺寸的MAPbI_3纳米立方块的带隙和光学性能出现了不同的变化规律。其中,小尺寸MAPbI_3纳米立方块,在0.25 GPa以下,带隙随着压力的增加一直减小,而对于大尺寸纳米立方块的带隙,在0.67 GPa以下,随着压力的增加持续增加。原位高压拉曼的测量和分析表明,尺寸效应与八面体[PbI_6]~(4-)和有机阳离子CH_3NH_3~+间的相互作用有关。我们的研究结果为深入了解低维有机-无机杂化钙钛矿纳米晶的带隙调控和光学特性以及结构稳定性提供了研究依据,为提高有机-无机杂化钙钛矿电池的转化效率开辟了一种研究思路。     

有机-无机杂化钙钛矿中的自旋输运和磁场效应

有机-无机杂化钙钛矿(OIHPs)是现阶段较为新颖的光电子材料之一,已被广泛地应用于太阳能电池和发光领域。然而,该类材料已被证实具有较强的自旋轨道耦合和Rashba效应,并且具备较高的载流子迁移率和消光系数。因此,这为实现自旋注入和自旋调控提供了重要依据。本文从三个方面对有机-无机杂化钙钛矿的自旋光电子学展开论述,首先是自旋极化电子在钙钛矿自旋器件中的输运研究以及铁磁-钙钛矿自旋界面研究;其次,是该材料在激发态下的磁场效应研究;最后,就钙钛矿自旋光电子学未来发展进行了探讨和评论。     

与腔场耦合的两个量子点中激子的纠缠动力学

利用共生纠缠度研究了单模腔场内两个耦合量子点中激子的纠缠动力学行为.结果表明:无论腔场初始制备于奇相干态还是偶相干态,两个量子点间直接耦合作用均能减弱激子的纠缠度.在腔场初始为奇相干态时,激子的纠缠度随场模强度的增加而减小;偶相干态时,激子的纠缠度呈现一个转折变化.此外,也研究了单模腔场内平均光子数与激子准最大相干纠缠态的关联.     

Optical properties of two-dimensional perovskites

The optical properties of two-dimensional (2D) perovskites recently receive numerous research focus thanks to the strong quantum and dielectric confinement effects. In addition to the strong excitonic effect at room temperature, 2D perovskites also have appealing features that their optical properties can be flexibly tuned by alternating organic or inorganic layers. Particularly, 2D chiral perovskites and 2D perovskites based heterostructures are emerging as new platforms to extend their functionalities. To optimize performance of 2D perovskites-based optoelectronic devices, it is critical to understand the fundamentals and explore the strategies to engineer their optical properties. This review begins with an introduction to the excitons and self-trapped excitons of 2D perovskites. Subsequently, inorganic/organic layer effects on optical properties and 2D perovskites based heterostructures are discussed. We also discussed the nonlinear optical properties of 2D perovskite. We are looking forward to that this review can stimulate more efforts to understand and optimize the optical properties of 2D perovskites.     

The influence of localized states on the optical absorption and carrier transport properties of acylamino hybrid perovskites with tunable electronic structures

Organic-inorganic hybrid perovskite solar cells have excellent optoelectronic properties, but their low thermal and chemical stabilities limit their commercial applications. In this paper, a new type of organic-inorganic hybrid perovskite is proposed. Malondiamide (MA,CH₂(CONH₂)₂) and propionamide (PA, CH₃CH₂CONH₂) were used as organic layers, with Pb-I octahedral inorganic layers to form quasi three-dimensional (3D) perovskites. The crystal structure, stability, electronic structure, and optical properties of MAPbI₄ and PAPbI₄ perovskites were investigated, and the results showed that there were localized states that corresponded to the number of acyl groups in the two perovskites. Energy band calculations showed that the localized states of the two perovskites rose above the bottom of the conduction band. This can be used to regulate the band gap of the two perovskites, which affects the electronic properties and optical absorption characteristics of the two perovskites. Compared with PAPbI₄, MAPbI₄ has a lower formation energy, lower band gap, lower effective mass of electrons and holes, wider energy range, and larger absorption coefficient, which indicates that MAPbI₄ is more suitable for use in solar cells. This study provides guidance for obtaining efficient and stable photovoltaic materials.     

Electronic structure of warm dense copper studied by ultrafast x-ray absorption spectroscopy

We use time-resolved x-ray absorption spectroscopy to investigate the unoccupied electronic density of states of warm dense copper that is produced isochorically through the absorption of an ultrafast optical pulse. The temperature of the superheated electron-hole plasma, which ranges from 4000 to 10?000 K, was determined by comparing the measured x-ray absorption spectrum with a simulation. The electronic structure of warm dense copper is adequately described with the high temperature electronic density of state calculated by the density functional theory. The dynamics of the electron temperature is consistent with a two-temperature model, while a temperature-dependent electron-phonon coupling parameter is necessary.     

Organometal Halide Perovskites: Bulk Low‐Dimension Materials and Nanoparticles

Organometal halide perovskites (hybrid perovskites) contain an anionic metal–halogen‐semiconducting framework and charge‐compensating organic cations. As hybrid materials, they combine useful properties of both organic and inorganic materials, such as plastic mechanical properties and good electronic mobility related to organic and inorganic material, respectively. They are prepared from abundant and low cost starting compounds. The perovskite stoichiometry is associated with the dimensionality of its inorganic framework, which can vary from three to zero, 3D consisting of corner‐sharing MX₆ octahedra, and 0D consisting of isolated octahedra. Small‐sized organic cations can fit into the MX₆ octahedra of the 3D framework and in all dimensions organic cations surround the inorganic framework. Regarding the low dimensionality in the material, this refers to at least one of its dimensions being shorter than approximately 100 nanometers. These materials should be considered as genuine nanomaterials or as bulk materials depending on whether they have three or less than three dimensions on the nanoscale, respectively. In principle, hybrid perovskite nanoparticles can be prepared with different shapes and with inorganic framework dimensionalities varying from 0D to 3D, and this also applies to the bulk material. This report is mainly focused on the unique properties of organometal halide perovskite nanoparticles.     

CdSe/ZnS纳晶中相干电声耦合效应的二维电子光谱研究

Coherent exciton-phonon coupling in CdSe/ZnS nanocrystals have been investigated by temperature-dependent two-dimensional electronic spectroscopy (2DES) measurements. Benefiting from the ability of 2DES to dissect assembles in nanocrystal films, we have clearly identified experimental evidences of coherent coupling between exciton and phonon in CdSe/ZnS nanocrystals. In time domain, 2DES signals of excitonic transitions beat at a frequency resonant to a longitudinal optical phonon mode; in energy domain, phonon side bands are distinct at both Stokes and anti-Stokes sides. When temperature increases, phonon-induced exciton dephasing is observed with dramatic broadening of homogeneous linewidth. The results suggest exciton-phonon coupling is essential in elucidating the quantum dynamics of excitonic transitions in semiconductor nanocrystals.     

Stability and optoelectronic property of low-dimensional organic tin bromide perovskites

The toxicity and degradation of hybrid lead-halide perovskites hinder their extensive applications.It is thus of great importance to explore non-toxic alternative materials with excellent stability and optoelectronic property.We investigate the atomic structures and optoelectronic properties of non-toxic organic tin bromide perovskites(OTBP)with one/zerodimensional(1D/0D)structures by first-principles calculations.The calculated atomic structures show that the 1D/0D OTBPs are stable and the structure of inorganic octahedra in 0D is higher order than that in 1D.Moreover,the origination of exceptional purity emitting light in experiments is explained based on the calculated electronic structure.     

Review of ultrafast spectroscopy studies of valley carrier dynamics in two-dimensional semiconducting transition metal dichalcogenides

The two-dimensional layered transition metal dichalcogenides provide new opportunities in future valley-based information processing and also provide an ideal platform to study excitonic effects. At the center of various device physics toward their possible electronic and optoelectronic applications is understanding the dynamical evolution of various manyparticle electronic states, especially exciton which dominates the optoelectronic response of TMDs, under the novel context of valley degree of freedom. Here, we provide a brief review of experimental advances in using helicity-resolved ultrafast spectroscopy, especially ultrafast pump–probe spectroscopy, to study the dynamical evolution of valley-related many-particle electronic states in semiconducting monolayer transitional metal dichalcogenides.     

Coherent dynamics of magnetoexcitons in semiconductor nanorings

The coherent dynamics of magnetoexcitons in semiconductor nanorings following pulsed optical excitation is studied. The calculated temporal evolution of the excitonic dipole moment may be understood as a superposition of the relative motion of electrons and holes and a global circular motion associated with the magnetic-field splitting of these states. This dynamics of the electron-hole pairs can be generated either by local optical excitation of an ordered ring or, alternatively, by homogeneous excitation of rings with broken rotational symmetry due to disorder or band tilting. Received 27 September 2000     

Fine structure of excitons in InAs/GaAs coupled auantum dots: a sensitive test of electronic coupling

Exciton fine structure in InAs/GaAs coupled quantum dots has been studied by photoluminescence spectroscopy in magnetic fields up to 8 T. Pronounced anticrossings and mixings of optically bright and dark states as functions of magnetic field are seen. A theoretical treatment of the mixing of the excitonic states has been developed, and it traces observed features to structural asymmetries. These results provide direct evidence for coherent coupling of excitons in quantum dot molecules.     

Picosecond timescale carrier dynamics of InAs quantum dots: The role of a continuum background

We have investigated the ultrafast carrier dynamics in Molecular Beam Epitaxy (MBE)-grown InAs/InGaAs/GaAs quantum dots emitting at 1.3 μm by means of time resolved photoluminescence upconversion measurements with a time resolution of about 200 fs. The detection energies scan the spectral region from the energy of the quantum dot excitonic transition up to the barrier layer absorption edge. We found, under high excitation intensity, that the intrinsic electronic states are populated mainly by carriers directly captured from the barrier.