Sn类钙钛矿太阳电池薄膜的掺杂改性研究

采用一步法分别制备了Sn类CH3NH3Sn I3和Pb类CH3NH3Pb I3钙钛矿太阳电池薄膜材料,并对其表面形貌、微观结构、吸收光谱和电池器件性能进行了表征和测试。研究结果表明:Sn类钙钛矿材料的吸收光谱相对于Pb类钙钛矿材料发生了明显的红移,吸收截止波长从800 nm上升到950 nm左右,光学带隙由1.45 e V降低至1.21 e V左右;Sn类钙钛矿材料的光谱吸收范围明显扩大,但吸收强度有所降低,相应太阳电池器件的光电转换效率也明显低于Pb类钙钛矿太阳电池,分别为2.05%和6.71%。而Br的掺杂可使Sn类钙钛矿材料带隙变宽,吸收光子能量增大,电池器件的开路电压也相应提高。当Br含量由0增加至完全替代I时,Sn类钙钛矿材料逐渐由黑褐色转变为黄色,光学带隙增大至1.95 e V,但吸收截止波长由950 nm降低至650nm。值得提及的是当Br含量为0.5时,电池器件的光电转换效率可由最初的2.05%提升至2.94%。     

功能性CdSe纳米晶的合成及自组装膜光致发光

以巯基丙酸(RSH)为稳定剂,采用湿化学法合成了功能性CdSe纳米晶,用XRD、TEM表征其粒度和形貌,用UV-Vis监测成核及成膜过程。结果表明：制得的CdSe近似呈球形,平均粒径为48 nm。利用静电自组装法层层组装成CdSe-PDDA复合膜,荧光测试表明：所得CdSe纳米晶自组装复合膜(CdSe-PDDA)的荧光强度随着组装层数的增加而呈线性增强,该复合膜在582 nm附近有黄绿色荧光发射。     

L-脯氨酸协助合成β-氢氧化镍和氧化镍花球及纳米三角片(英文)

以NH3·H2O和NaOH作为沉淀剂,通过水热方法在180℃,L-脯氨酸作用下,分别合成出了β-Ni(OH)2花球和纳米三角片。XRD结果表明合成出的β-Ni(OH)2产物是六方相,透射电镜(TEM)和场发射电镜(FESEM)表明花球直径为1~2μm,它是由厚15nm,边长110nm的三角片自组装形成的。对相应的β-Ni(OH)2前驱物在350℃空气下退火2h,分别得到NiO花球和纳米三角片。     

反相微乳液水热法自组装LaF3纳米晶制备新型一维LaF3纳米链

采用反相微乳液水热法自组装LaF<,3>纳米晶成功制备了新型的一维LaF<,3>纳米链(1),其结构和性能经XRD,TEM,HR-TEM和XPS表征.结果表明:1由粒径为30 nm～40 nm的纳米晶背靠背连接而成,单个纳米晶结晶良好,连接处既有晶态也有非晶态.提出了纳米晶自组装成纳米链的可能机理.     

Gd2O3∶Eu3+纳米棒的制备与发光性能

在表面活性剂辅助的水热条件下合成出尺寸均一的Gd2O3∶Eu3+纳米棒, 对其结构和荧光性质进行了表征, 并对其生长机理进行了初步讨论. XRD结果表明, 水热前驱体样品为六方晶相的Gd(OH)3, 经过灼烧之后样品为立方相的Gd2O3. TEM照片表明, 所得样品为直径60 nm、长度约600 nm的纳米棒. 荧光光谱表明, 在波长为254 nm 的紫外光激发下, Gd2O3∶Eu3+纳米棒产生了不同于前驱体的特征红光发射, 对应于Eu3+ 的5D0-7F2跃迁, 表明Gd2O3是红色发光材料的良好基质.     

离子液体{[C16mim]Br}辅助CdS纳米球的制备

以CdCl2·2.5H2O和Na2S2O3为原料,在[C16mim]Br离子液体中合成了CdS纳米球(1),其结构和性能经XRD和TEM表征。考察了c{[C16mim]Br}对1形貌的影响,结果表明,通过控制c{[C16mim]Br},可制得分散性较好,粒径在50 nm～80 nm的1。     

水热法制备多层核壳结构Gd2O3∶Eu3+空心微球

以稀土硝酸盐-葡萄糖的混合溶液作为前驱体,采用一步水热法和随后的热处理得到了多层核壳结构Gd₂O₃∶Eu³⁺空心微球,并用X-射线衍射(XRD)、场发射扫描电镜(FESEM)、透射电镜(TEM)、X-射线能量色散光谱(EDS)和荧光光谱等测试手段对所得样品进行了表征。结果表明：所得空心球样品为纯的立方相的Gd₂O₃。具有规则的多层核壳空心结构,空心球的直径在2~3 μm左右,壁厚约为100 nm,并且Gd₂O₃∶Eu³⁺空心球是由尺寸约为30 nm的球形纳米颗粒自组装而成。样品中含有Gd、Eu、O元素。该空心球样品具有强的Eu³⁺的特征红光发射以及长的荧光寿命,可以用来作为时间分辨荧光标记物。     

Fe3O4纳米晶的简单调控合成、表征及磁性能

采用醋酸铵作保护剂在200℃下制备了单分散的400 nm粒径的Fe3O4空心纳米球.通过改变实验条件,对产品的形貌、内部结构和粒径进行了调控合成,得到了粒径范围在100～200 nm的实心纳米球和片形结构的Fe3O4纳米材料.采用SEM、TEM和XRD等对样品进行了表征.结果表明,所得尖晶石型Fe3O4纳米晶粒径均匀,分散度好.利用振动样品磁场计检测了不同形貌样品的磁性能.结果显示,Fe3O4纳米空心球的饱和磁化强度和矫顽力均大于Fe3O4纳米片的对应值.     

Ag@YF3:Eu3+核壳结构纳米材料的制备与性能研究

采用乙二醇法制备了单质Ag纳米粒子,并通过直接沉淀法合成了均匀球形的Ag@YF3∶Eu3+核壳结构复合纳米发光粒子,对产物的结构和性能进行了表征。XRD分析表明:Ag表面包覆上了结晶良好的正交晶系的YF3∶Eu3+。TEM照片表明:所得的纳米复合粒子具有明显的核壳结构和均匀的球形,中间Ag粒子的尺寸在80~100 nm之间,Ag@YF3∶Eu3+的粒径尺寸约为150~180 nm,表面粗糙且包覆完全。电子衍射表明复合样品为多晶。荧光光谱表明:该纳米复合粒子具有良好的发光性,以593 nm附近的5D0→7F1磁偶极跃迁为最强发射峰,但是比纯的YF3∶Eu3+的发光强度要弱,其荧光寿命有所增强,这表明Ag纳米粒子对外层的YF3∶Eu3+的发光有猝灭作用。     

多层多孔Co3O4纳米粒子组装体的合成、表征和电化学性能研究

利用十二烷基磺酸钠(SDS)作为表面活性剂,合成了形貌化的CoC₂O₄配合物前驱物,然后在500 ℃下热分解形貌化的前驱物,得到了多层多孔Co₃O₄纳米粒子组装体。采用FESEM、TEM、HRTEM、XRD、N₂吸附脱附和Raman散射等手段对产物进行了分析和表征。低角XRD,TEM和N₂吸附脱附测试表明所得组装体具有多孔结构。常规XRD、HRTEM和Raman结果证明组装体中Co₃O₄纳米粒子建筑块结晶较好。与体相Co₃O₄晶体相比,Co₃O₄纳米粒子组装体的5个拉曼活性峰发生了明显的红移。将Co₃O₄纳米粒子组装体作为锂离子电池的正极材料进行了电化学性能测试,结果表明该组装体电极的首次放电容量为1 115 mAh·g^-1,远高于目前文献报道的Co₃O₄纳米管、纳米粒子和纳米棒电极。但是,该组装体电极的循环性能不好,有待进一步提高。     

Colloidal Synthesis of CH3NH3PbBr3 Nanoplatelets with Polarized Emission through Self‐Organization

We report a combined experimental and theoretical study of the synthesis of CH₃NH₃PbBr₃ nanoplatelets through self‐organization. Shape transformation from spherical nanodots to square or rectangular nanoplatelets can be achieved by keeping the preformed colloidal nanocrystals at a high concentration (3.5 mg mL⁻¹) for 3 days, or combining the synthesis of nanodots with self‐organization. The average thickness of the resulting CH₃NH₃PbBr₃ nanoplatelets is similar to the size of the original nanoparticles, and we also noticed several nanoplatelets with circular or square holes, suggesting that the shape transformation experienced a self‐organization process through dipole–dipole interactions along with a realignment of dipolar vectors. Additionally, the CH₃NH₃PbBr₃ nanoplatelets exhibit excellent polarized emissions for stretched CH₃NH₃PbBr₃ nanoplatelets embedded in a polymer composite film, showing advantageous photoluminescence properties for display backlights.     

1,2-Eliminations from (CH3)2NH+CH2CH3 and (CH3)2NH 2+ : Guided dissociations

1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations, elimination of CH₂=CH₂ and CH₃CH₃ from (CH₃)₂NH⁺CH₂CH₃ (1) and of CH₄ from (CH₃)₂NH₂⁺ are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from methyl to the bridging position in ethyl and then to N to reach (CH₃)₂NH₂⁺ + CH₂=CH₂ from 1. CH₃CH₃ elimination by H-transfer to C₂H₅⁺ to form CH₃NH⁺=CH₂ + CH₃CH₃ also takes place. (CH₃)₂NH₂⁺ eliminates methane by CN bond extension followed by β-H-transfer to give CH₂=NH⁺ + CH₄. Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type of reaction. As in many complex-mediated reactions, these reactions transfer H between incipient fragments. They are distinguished from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described lower energy reactions, have 1,1-like transition states, or utilize highly asynchronous 1,2 transition states. All of these avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry.     

Understanding the Impact of Bismuth Heterovalent Doping on the Structural and Photophysical Properties of CH3NH3PbBr3 Halide Perovskite Crystals with Near-IR Photoluminescence

A comprehensive study unveiling the impact of heterovalent doping with Bi³⁺ on the structural, semiconductive, and photoluminescent properties of a single crystal of lead halide perovskites (CH₃NH₃PbBr₃) is presented. As indicated by single-crystal XRD, a perfect cubic structure in Bi³⁺-doped CH₃NH₃PbBr₃ crystals is maintained in association with a slight lattice contraction. Time-resolved and power-dependent photoluminescence (PL) spectroscopy illustrates a progressively quenched PL of visible emission, alongside the appearance of a new PL signal in the near-infrared (NIR) regime, which is likely to be due to energy transfer to the Bi sites. These optical characteristics indicate the role of Bi³⁺ dopants as nonradiative recombination centers, which explains the observed transition from bimolecular recombination in pristine CH₃NH₃PbBr₃ to a dominant trap-assisted monomolecular recombination with Bi³⁺ doping. Electrically, it is found that the mobility in pristine perovskite crystals can be boosted with a low Bi³⁺ concentration, which may be related to a trap-filling mechanism. Aided by temperature (T)-dependent measurements, two temperature regimes are observed in association with different activation energies (E_a) for electrical conductivity. The reduction of E_a at lower T may be ascribed to suppression of ionic conduction induced by doping. The modified electrical properties and NIR emission with the control of Bi³⁺ concentration shed light on the opportunity to apply heterovalent doping of perovskite single crystals for NIR optoelectronic applications.     

Halogen in materials design: Revealing the nature of hydrogen bonding and other non-covalent interactions in the polymorphic transformations of methylammonium lead tribromide perovskite

Methylammonium lead tribromide (CH₃NH₃PbBr₃) perovskite as a photovoltaic material has attracted a great deal of recent interest. Factors that are important in their application in optoelectronic devices include their fractional contribution of the composition of the materials as well as their microscopic arrangement that is responsible for the formation of well-defined macroscopic structures. CH₃NH₃PbBr₃ assumes different polymorphs (orthorhombic, tetragonal and cubic) depending on the evolution temperature of the bulk material. An understanding of the structure of these compounds will assist in rationalizing how halogen-centered non-covalent interactions play an important role in the rational design of these materials. Density functional theory (DFT) calculations have been performed on polymorphs of CH₃NH₃PbBr₃ to demonstrate that the H atoms on C of the methyl group in CH₃NH₃⁺ entrapped within a PbBr₆^4? perovskite cage are not electronically innocent, as is often contended. We show here that these H atoms are involved in attractive interactions with the surrounding bromides of corner-sharing PbBr₆^4? octahedra of the CH₃NH₃PbBr₃ cage to form Br?H(C) hydrogen bonding interactions. This is analogous to the way the H atoms on N of the NH₃⁺ group in CH₃NH₃⁺ form Br?H(N) hydrogen bonding interactions to stabilize the structure of CH₃NH₃PbBr₃. Both these hydrogen bonding interactions are shown to persist regardless of the nature of the three polymorphic forms of CH₃NH₃PbBr₃. These, together with the Br?C(N) carbon bonding, the Br?N(C) pnictogen bonding, and the Br?Br lump-hole type intermolecular non-covalent interactions identified for the first time in this study, are shown to be collectively responsible for the eventual emergence of the orthorhombic geometry of the CH₃NH₃PbBr₃ system. These conclusions are arrived at from a systematic analysis of the results obtained from combined DFT, Quantum Theory of Atoms in Molecules (QTAIM), and Reduced Density Gradient Non-Covalent Interaction (RDG-NCI) calculations carried out on the three temperature-dependent polymorphic geometries of CH₃NH₃PbBr₃.     

溶胶凝胶法合成Li3V6O16及其电化学性能研究

本文以双氧水为配位剂,以CH3COOLi·2H2O和V2O5为原料,采用溶胶凝胶法合成了一种新型的晶体Li3V6O16。随后分别采用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和电子衍射(SAED)、X光电子能谱(XPS)和充放电测试等手段对材料进行了表征。SEM观察表明,产物主要是表面比较光滑的纳米片状晶体,TEM和SAED研究都证实了XRD和SEM的研究结果。充放电测试结果表明,该物质具有较高的比容量、良好的可逆性和循环稳定性。     

Synergistic Surface Passivation of CH3NH3PbBr3 Perovskite Quantum Dots with Phosphonic Acid and (3-Aminopropyl)triethoxysilane

CH₃NH₃PbBr₃ perovskite quantum dots (PQDs) are synthesized by using four different linear alkyl phosphonic acids (PAs) in conjunction with (3-aminopropyl)triethoxysilane (APTES) as capping ligands. The resultant PQDs are characterized by means of XRD, TEM, Raman spectroscopy, FTIR spectroscopy, UV/Vis, photoluminescence (PL), time-resolved PL, and X-ray photoelectron spectroscopy (XPS). PA chain length is shown to control the PQD size (ca. 2.9–4.2 nm) and excitonic absorption band positions (λ=488–525 nm), with shorter chain lengths corresponding to smaller sizes and bluer absorptions. All samples show a high PL quantum yield (ca. 46–83 %) and high PL stability; this is indicative of a low density of band gap trap states and effective surface passivation. Stability is higher for smaller PQDs; this is attributed to better passivation due to better solubility and less steric hindrance of the shorter PA ligands. Based on the FTIR, Raman, and XPS results, it is proposed that Pb²⁺ and CH₃NH₃⁺ surface defects are passivated by R−PO₃²⁻ or R−PO₂(OH)⁻, whereas Br⁻ surface defects are passivated by R−NH₃⁺ moieties. This study establishes the combination of PA and APTES ligands as a highly effective dual passivation system for the synergistic passivation of multiple surface defects of PQDs through primarily ionic bonding.     

Self‐Template‐Directed Synthesis of Porous Perovskite Nanowires at Room Temperature for High‐Performance Visible‐Light Photodetectors

The unique optoelectronic properties and promising photovoltaic applications of organolead halide perovskites have driven the exploration of facile strategies to synthesize organometal halide perovskites and corresponding hybrid materials and devices. Currently, the preparation of CH₃NH₃PbBr₃ perovskite nanowires, especially those with porous features, is still a great challenge. An efficient self‐template‐directed synthesis of high‐quality porous CH₃NH₃PbBr₃ perovskite nanowires in solution at room temperature using the Pb‐containing precursor nanowires as both the sacrificial template and the Pb²⁺ source in the presence of CH₃NH₃Br and HBr is now presented. The initial formation of CH₃NH₃PbBr₃ perovskite layers on the surface of the precursor nanowires and the following dissolution of the organic component of the latter led to the formation of mesopores and the preservation of the 1D morphology. Furthermore, the perovskite nanowires are potential materials for visible‐light photodetectors with high sensitivity and stability.     

The infrared spectrum and force field of the methyl-ammonium ion in (CH3NH3)2PtCl6

Infrared spectra of the CH₃NH₃⁺, CH₃ND₃⁺, CD₃NH₃⁺ and CD₃ND₃⁺ ions in bis(methylammonium)hexachloroplatinate(IV) have been recorded. The spectra are entirely consistent with the C_3v symmetry reported for the methylammonium ion, at temperatures between room temperature and 90 K. No spectral manifestations of the phase transition, which in (CH₃NH₃)₂PtCl₆ has been reported to take place at 125 K, were observed. Assignments of the infrared-active fundamentals have been made for each ion and a normal-coordinate analysis has been performed using the observed fundamental frequencies. Comparison with the infrared spectra of other methylammonium salts shows that hydrogen bonding in (CH₃NH₃)₂PtCl₆, if present, is weak.     

Top‐Down Fabrication of Stable Methylammonium Lead Halide Perovskite Nanocrystals by Employing a Mixture of Ligands as Coordinating Solvents

A top‐down method is demonstrated for the fabrication of CH₃NH₃PbBr₃ and CH₃NH₃PbI₃ perovskite nanocrystals, employing a mixture of ligands oleic acid and oleylamine as coordinating solvents. This approach avoids the use of any polar solvents, skips multiple reaction steps by employing a simple ultrasonic treatment of the perovskite precursors, and yields rather monodisperse blue‐, green‐, and red‐emitting methylammonium lead halide nanocrystals with a high photoluminescence quantum yield (up to 72 % for the green‐emitting nanocrystals) and remarkably improved stability. After discussing all relevant reaction parameters, the green‐emitting CH₃NH₃PbBr₃ nanocrystals are employed as a component of down‐conversion white‐light‐emitting devices_.     

Theoretical study on halide and mixed halide Perovskite solar cells: Effects of halide atoms on the stability and electronic properties

Increasing the stability of perovskite solar cells is one of the most important tasks in the photovoltaic industry. Thus, the structural, energetic, and electronic properties of pure CH₃NH₃PbI₃ and fully doped compounds (CH₃NH₃PbBr₃ and CH₃NH₃PbCl₃) in cubic and tetragonal phases were investigated using density functional theory calculations. We also considered the effects of mixed halide perovskites CH₃NH₃PbI₂X (where X = Br and Cl) and compared their properties with CH₃NH₃PbI₃. The DFT results indicate that the phase transformation from tetragonal to cubic phase decreases the band gap. The calculated results show that the X‐site ion plays a vital role in the geometrical stability and electronic levels. An increase in the band gap and a reduction in the lattice constants are more apparent in CH₃NH₃PbI₂X compounds (I > Br > Cl).