Nanocomposite thin film structures based on polyarylenephthalide with SWCNT and graphene oxide fillers

Investigations of nanocomposite thin films based on polyarylene- phthalide, single-walled carbon nanotubes and graphene oxide have been carried out. Using these films as a transport layer, field-effect transistors were assembled and their output and transfer characteristics were measured. The mobility of charge carriers was estimated and the obtained values are as follows: μ_PAP/GO = 0.020 cm² V^?1 s^?1 and μ_PAP/SWCNT = 0.071 cm² V^?1 s^?1.     

Evaluation of Charged Defect Energy in Two-Dimensional Semiconductors for Nanoelectronics: The WLZ Extrapolation Method

Defects play a central role in controlling the electronic properties of two-dimensional (2D) materials and realizing the industrialization of 2D electronics. However, the evaluation of charged defects in 2D materials within first-principles calculation is very challenging and has triggered a recent development of the WLZ (Wang, Li, Zhang) extrapolation method. This method lays the foundation of the theoretical evaluation of energies of charged defects in 2D materials within the first-principles framework. Herein, the vital role of defects for advancing 2D electronics is discussed, followed by an introduction of the fundamentals of the WLZ extrapolation method. The ionization energies (IEs) obtained by this method for defects in various 2D semiconductors are then reviewed and summarized. Finally, the unique defect physics in 2D dimensions including the dielectric environment effects, defect ionization process, and carrier transport mechanism captured with the WLZ extrapolation method are presented. As an efficient and reasonable evaluation of charged defects in 2D materials for nanoelectronics and other emerging applications, this work can be of benefit to the community.     

Everything you wanted to know about phase and reference frequency in one- and two-dimensional NMR spectroscopy

The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse and the receiver can be used to change the reference frequency along direct and indirect dimensions of NMR experiments. Unusual of phase incrementation with non-90° angles will be illustrated on one- and two-dimensional NMR spectra.     

Computational Study on the Charge Transport and Optical Spectra of Anthracene Derivatives in Aggregates

A recent experiment [Angew. Chem. Int. Ed. 2017 , 56, 722–727] found that a (1 : 9) blend film of two anthracene derivatives, 2-fluorenyl-2-anthracene ( FlAnt ) and 2-anthryl-2-anthracence ( 2 A ), exhibit both efficient white light emission and high hole mobility, thus promising for organic light-emitting transistors (OLETs). Employing quantum chemistry at the polarizable continuum model (PCM) and the quantum mechanics/molecular mechanics (QM/MM) levels, we investigated the excited-state structures, optical spectra, band structure and the carrier mobility for FlAnt and 2 A from solution to aggregate phases. We suggest using the ratio of intermolecular excitonic coupling J and intramolecular excited state relaxation energy E to judge the bathochromic shift in optical emission in aggregates. For FlAnt , ρ=J/E is calculated to be less than 0.17, a critical value we identified earlier, and the spectra in solution and aggregate phases present quite similar features (blue emission). However, ρ is ∼0.5 for 2 A systems, and the calculated emission in the aggregate phase exhibits a remarkable bathochromic shift. In addition, the 0–0 emission is strongly suppressed in the herringbone stacking. These observations justify the experimental findings that (i) 2 A is blue emissive in solution but yellow-green in the aggregate phase, whereas FlAnt is always blue, and (ii) the blend of them show white emission. By using the “quantum nuclear tunneling” model we proposed earlier, we found the hole mobility for FlAnt and 2 A are 0.5 and 4.2 cm² V⁻¹ s⁻¹, respectively, indicating both are good hole transport materials.     

基于混合空穴注入层的湿法制备高效蓝光热激活延迟有机发光二极管

在溶液法制备有机电致发光器件(OLEDs)的研究中, PEDOT∶PSS由于具有较好的成膜性与高透光性而常被用作器件的空穴注入层。但相关研究表明, PEDOT∶PSS本身稳定性较差以及功函数较低,这使得溶液法制备OLEDs的性能差且不稳定。蓝色作为全彩色的三基色之一,制备高效的蓝光器件对于实现高质量显示器件和固态照明装置必不可少。而目前溶液法制备蓝光OLEDs的器件效率普遍较差,针对此问题,本文利用传统的蓝光热激活延迟荧光发光(TADF)材料DMAC-DPS作为发光层,用溶液法制备了蓝光TADF OLEDs,通过在PEDOT∶PSS中掺杂PSS-Na制备混合空穴注入层(mix-HIL)来提高空穴注入层的功函数,研究其对于蓝光TADF OLEDs器件性能的影响。首先在PEDOT∶PSS水溶液中掺入不同体积的PSS-Na溶液,在相同条件下旋涂制膜,进行器件制备。通过观测各个实验组器件的电致发光(EL)光谱,发现掺入PSS-Na后器件EL谱存在光谱蓝移的现象,这是由于掺入PSS-Na水溶液后, mix-HIL层的厚度有所降低,使得在微腔效应作用下, EL光谱发生蓝移。通过对比各组器件的电流密度-电压-亮度(J-V-L)曲线及其计算所得器件的电流效率,结果显示随着PSS-Na的掺入,器件的亮度和电流都有所增大,器件的电流效率也得到了提升,当掺杂比例为0.5∶0.5(PEDOT∶PSS/PSS-Na)时提升幅度最大(亮度提升86.7%,电流效率提升34.3%)。通过在瞬态电致发光测试过程中施加或撤去驱动电压观测了器件EL强度的变化,分析了在混合空穴注入层/发光层(mix-HIL/EML)界面处的电荷积累情况。实验证明,通过在PEDOT∶PSS中掺杂PSS-Na制备mix-HIL获得了蓝光TADF OLEDs器件性能的提升,这是一个获得高效率溶液法制备OLEDs的可行方法。     

基于石墨烯独特生物界面效应的功能化载体研究进展

二维石墨烯及其衍生物与生物界面的相互作用, 展现出相比于传统维度粒子截然不同的特性, 为功能化医药载体的设计开发提供了潜力策略. 除了优异的电学、热学、光学等性能外, 石墨烯的独特的二维性质, 可以引起细胞更强的应激反应, 包括与细胞膜发生水平摩擦/竖直嵌入/三明治超级结构、选择性被细胞内吞、胞内限域折叠、引发细胞自噬以及隐形活化效应. 基于上述独特界面效应以及理论模拟机制, 对石墨烯进行合理设计, 可在保障安全性的前提下, 满足药物递送、疫苗佐剂、成像传感、光热治疗等需求. 本综述结合课题组近10年在(氧化)石墨烯与生物界面效应、微观作用机理及应用开发方面的系统研究工作, 同时涵盖了国际最新进展, 以期为石墨烯高效、安全体系的设计、构建和应用, 提供理论依据和前瞻性预测.     

SAPO-34提升铁钒基催化剂抗碱性能研究

采用浸渍法制备Fe-VO_x/SAPO-34和Fe-VO_x/TiO₂脱硝催化剂,探究SAPO-34分子筛与TiO₂两种载体负载铁钒基氧化物催化活性及抗碱性能的差异。借助X射线衍射(XRD)、X射线光电子能谱(XPS)、氨气程序升温脱附(NH₃-TPD)、氢气程序升温还原(H₂-TPR)、原位红外漫反射(in-situ DRIFTs)等表征手段对催化剂的骨架结构、表面物化性质、氧化还原能力以及对反应气体的吸脱附情况进行分析。结果表明:SAPO-34分子筛内部特定的孔道结构和稳定的骨架,有利于活性组分在载体上均匀分散,降低碱金属对表面活性中心的物理覆盖作用;同时其表面丰富的酸位点能够作为碱金属捕获位,保护催化剂表面的活性中心,保证催化剂的吸附-反应过程能够正常进行,从而使Fe-VO_x/SAPO-34表现出良好的抗碱金属能力。     

染料敏化太阳能电池载流子传输的数值模拟

由于在染料敏化太阳能电池(dye-sensitized solar cell, DSSC)中存在染料弛豫、半导体薄膜中电子与氧化态染料分子发生反应和电子在电解质中与氧化态离子复合等不利反应,利用一个更完善的DSSC载流子传输模型对电池的光电性能进行模拟就显得非常重要。为此,本文基于由多重俘获理论建立的DSSC中的包括电子、染料阳离子、碘化物和三碘化物在内的载流子传输模型,数值模拟得到了不同TiO₂薄膜厚度、不同入射光强度与不同染料分子吸收系数下DSSC的J-V曲线。结果表明,随着TiO₂薄膜厚度的增加,太阳能电池的短路电流密度增大,开路电压减小,光电转换效率先增大后减小。当DSSC的TiO₂薄膜厚度为20 μm时,光电转换效率达到最大值7.41%,同时光电转换效率随入射光强度与染料分子吸收系数的增大均有一定程度提高,其中在吸收系数为4 500 cm^-1时,光电转换效率为6.73%。以上结果可以为改进DSSC的光电性能提供理论指导。     

Photophysics of a Ruthenium 4H‐Imidazole Panchromatic Dye in Interaction with Titanium Dioxide

The photophysics of bis(4,4′‐di‐tert‐butyl‐2,2′‐bipyridine‐κ²N,N′)[2‐(4‐carboxyphenyl)‐4,5‐bis(p‐tolylimino‐κN)imidazolato]ruthenium(II) hexafluorophosphate is investigated, both in solution and attached to a nanocrystalline TiO₂ film. The studied substitution pattern of the 4H‐imidazole ligand is observed to block a photoinduced structural reorganization pathway within the 4H‐imidazole ligand that has been previously investigated. Protonation at the 4H‐imidazole ring decreases the excited‐state lifetime in solution. When the unprotonated dye is anchored to TiO₂, photoinduced electron injection occurs from thermally nonrelaxed triplet metal‐to‐ligand charge transfer (³MLCT) states with a characteristic time constant of 0.5 ps and an injection efficiency of roughly 25 %. Electron injection from the subsequently populated thermalized ³MLCT state of the dye does not take place. The energy of this state seems to be lower than the conduction band edge of TiO₂.     

Two‐Dimensional Haeckelite NbS2: A Diamagnetic High‐Mobility Semiconductor with Nb4+ Ions

In all known Group 5 transition‐metal dichalcogenide monolayers (MLs), the metal centers carry a spin, and their ground‐state phases are either metallic or semiconducting with indirect band gaps. Here, on grounds of first‐principles calculations, we report that the Haeckelite polytypes 1 S ‐NbX₂ (X=S, Se, Te) are diamagnetic direct‐band‐gap semiconductors even though the Nb atoms are in the 4+ oxidation state. In contrast, 1 S ‐VX₂ MLs are antiferromagnetically coupled indirect‐band‐gap semiconductors. The 1 S phases are thermodynamically and dynamically stable but of slightly higher energy than their 1 H and 1 T ML counterparts. 1 S ‐NbX₂ MLs are excellent candidates for optoelectronic applications owing to their small band gaps (between 0.5 and 1 eV). Moreover, 1 S ‐NbS₂ shows a particularly high hole mobility of 2.68×10³ cm² V⁻¹ s⁻¹, which is significantly higher than that of MoS₂ and comparable to that of WSe₂.