高分子光电功能材料及其应用:平板显示,白光照明,太阳电池

近年来共轭高分子材料作为光电信息及能源相关的功能材料与器件研究发展十分迅速,引起学界与产业界极大的关注与参与。90年代开始的有机/高分子电致发光材料与器件的研究目前已经发展成新的一代平板显示产业,小尺寸OLED显示屏的产值达到8.26亿美元。由于O/PLED具有驱动电压低,宽发光,响应速度快;超薄,重量轻,全固化主动发光;可制作在柔性衬底上等一系列优点,被认为是下一代大屏幕平板显示的首选。近年来由于能源危机,白光照明计划成为各国长远节能计划的重点。与我国该计划只重视无机发光二极管(GaN)不同,美欧都将成本较低的平面O/PLED白光照明板的研究放到很重要的地位。太阳能是最重要的可再生能源之一。近年来大面积聚合物异质结太阳电池成为目前有机/高分子光电材料器件研究的最热点。本文将针对高分子光电材料在这三种应用领域的研究近况,主要拟解决的科学问题,及产业化前景及本实验室最近的主要进展做简要报告。     

Electrically tunable dielectric materials and strategies to improve their performances

Electrically tunable dielectric materials have potential applications as various microwave devices, such as tunable oscillators, phase shifters and varactors. High dielectric tunability, low dielectric loss tangent and appropriate level of dielectric constant, are basic requirements for such applications. Ferroelectric materials are the most promising candidates. In general, strontium titanate (SrTiO₃ or ST) is used for devices operating at low temperatures, while the devices based on barium strontium titanate (Ba_1?xSr_xTiO₃ or BST) are operated at room temperatures. The modifications of parent ferroelectrics, such as Sr_1?xPb_xTiO₃, BaZr_xTi_1?xO₃ and BaTi_1?xSn_xO₃ etc., have also been widely investigated. In addition, there have been reports on electrically tunable dielectric materials, based on non-ferroelectric compounds, such as microwave dielectrics and carbon nanotube (CNT) composites. Specifically for ferroelectric materials, a critical issue is the reduction of the dielectric losses, because their dielectric loss tangents are relatively high for practical device applications. Recently, many efforts have been made in order to reduce the dielectric losses of BST based ferroelectrics. An efficient way is to dope oxides that have low dielectric losses, such as MgO, ZrO₂ and Al₂O₃, TiO₂, LaAlO₃, and Bi_1.5ZnNb_1.5O₇ etc., into the ferroelectric materials. In addition to the reduction in dielectric loss tangents, the introduction of oxides would also be able to modify the dielectric constant to be suitable for practical design of various devices. Meanwhile, dielectric and electrical properties of thin films can be improved by chemical doping, substrate adaptation, orientation and anisotropy optimization. This review provides an overall summary on the recent progress in developing electrically tunable dielectric materials, based on ferroelectrics and non-ferroelectrics, with a specific attention to the strategies employed to improve the performances of ferroelectric materials for microwave device applications.     

Recent progress in bismuth-based high Curie temperature piezo-/ferroelectric perovskites for electromechanical transduction applications

Piezo-/ferroelectric materials with high Curie temperature (T_C) are widely needed in sensors, actuators and transducers which can be used for high-temperature (HT) electromechanical transduction applications. In recent years, remarkable progress has been made in bismuth-based piezo-/ferroelectric perovskite materials (BPPs). In this article, recent progress in high T_C BPPs is reviewed. This review starts with an introduction to HT piezoelectrics and their applications. A detailed survey is then carried out on bismuth-based perovskites (BPs) with high T_C. Material synthesis, doping effects and chemical modifications of the related solid solutions are examined. Based on this analysis, the structure–property relationship of these materials is established. In addition, recent developments of BPPs for HT electromechanical transduction applications are presented and evaluated. Lastly, some main existing issues are analyzed and their possible solutions are proposed. This article provides a comprehensive overview of the research and development of BPPs and offers some prospects towards making these materials a viable resource for the design and fabrication of electromechanical transducers with unique specifications, especially, high temperature, high frequency and high power, for a wide range of technological applications.     

Infrared Quantum Dots

Colloidal nanocrystals are quantum‐size‐effect tunable; offer an abundance of available surface area for electronic and chemical interactions; and are processible from organic or aqueous solution onto substrates rigid or flexible, smooth or rough, flat or curved, inorganic or organic (including biological), crystalline or amorphous, conducting, semiconducting, or insulating. With the benefit of over a decade's progress in visible‐light‐emitting colloidal‐quantum‐dot synthesis, physical chemistry, and devices, significant progress has recently been made in infrared‐active colloidal quantum dots and devices. This progress report summarizes the state‐of‐the‐art in infrared colloidal quantum dots, with an emphasis on applications and devices. The applications of interest surveyed include monolithic integration of fiber‐optic and free‐space‐communications photonic components with electronic substrates such as silicon and glass; in‐vivo biological tagging in infrared spectral bands in which living tissue is optically penetrable to a depth of 5–10 cm; solar and thermal photovoltaics for energy conversion; and infrared sensing and imaging based on non‐visible, including thermal, signatures. The synthesis and properties of quantum dots are first reviewed: photoluminescence quantum efficiencies greater than 50 % are achievable in solution, and stable luminescent dots are available in organic and aqueous solvents. Electroluminescent devices based on solution processing have been reported with external quantum efficiencies approaching 1 %. Photoconductive devices have been realized with 3 % internal quantum efficiencies, and a photovoltaic effect was recently observed. Electro‐optic modulation achieved by either field‐ or charge‐induced modification of the rate of optical absorption has been demonstrated based both on interband and intersubband (intraband) transitions. Optical gain from these processible materials with a threshold of 1 mJ cm^–2 and an optical net modal gain coefficient of 260 ± 20 cm^–1 have been reported.     

Structure,properties, and MEMS and microelectronic applications of vanadium oxides

Vanadium oxides have for many decades attracted much attention for their rich and unique physical properties which pose intriguing questions as to their fundamental origins as well as offering numerous potential applications for microelectronics, sensors, and microelectromechanical systems (MEMS). This paper reviews the unique structure and properties of the two most common vanadium oxides which have entered into microfabricated devices, VO₂ and V₂O₅, and some of the past and future device applications which can be realized using these materials. Two emerging new materials, sodium vanadium bronzes and vanadium oxide nanotubes are also discussed for their potential use in new microelectronic devices.     

New research opportunities in superconductivity IV

This report surveys the considerable progress made over the last five years—such as the marketing of superconducting quantum interference devices (SQUIDs), cellular wireless filter systems, and high current leads—and assesses needs and opportunities in the areas of fundamental science, materials development, thin film and device applications, and wire and bulk applications. It examines the challenges facing high-temperature superconductivity: from the need to understand the mechanism of high-temperature superconductivity and the unusual “normal” state to the need for new instrumentation for material characterization. Advances in thin film and bulk materials are reviewed, and obstacles impeding the commercialization of HTS materials are examined. A report on the workshop on research needs and opportunities in superconductivity, held in Monterey, California, February 10–12, 1997.     

Recent progress in transparent oxide semiconductors: Materials and device application

This paper reviews our recent research progress on new transparent conductive oxide (TCO) materials and electronic and optoelectronic devices based on these materials. First, described are the materials including p-type materials, deep-UV transparent TCO(β-Ga₂O₃), epitaxially grown ITO with atomically flat surface, transparent electrochromic oxide (NbO₂F), amorphous TCOs, and nanoporous semiconductor 12CaO · 7Al₂O₃. Second, presented are TCO-based electronic/optoelectronic devices realized to date, UV/blue LED and UV-sensors based on transparent pn junction and high performance transparent TFT using n-type TCO as an n-channel. Finally, unique optoelectronic properties (p-type degenerate conduction, transfer doping of carriers, RT-stable exciton, and large optical nonlinearity) originating from 2D-electronic nature in p-type layered oxychalcogenides are summarized along with the fabrication method of epitaxial thin films of these materials.     

A Strategy to Design High‐Density Nanoscale Devices utilizing Vapor Deposition of Metal Halide Perovskite Materials

The demand for high memory density has increased due to increasing needs of information storage, such as big data processing and the Internet of Things. Organic–inorganic perovskite materials that show nonvolatile resistive switching memory properties have potential applications as the resistive switching layer for next‐generation memory devices, but, for practical applications, these materials should be utilized in high‐density data‐storage devices. Here, nanoscale memory devices are fabricated by sequential vapor deposition of organolead halide perovskite (OHP) CH₃NH₃PbI₃ layers on wafers perforated with 250 nm via‐holes. These devices have bipolar resistive switching properties, and show low‐voltage operation, fast switching speed (200 ns), good endurance, and data‐retention time >10⁵ s. Moreover, the use of sequential vapor deposition is extended to deposit CH₃NH₃PbI₃ as the memory element in a cross‐point array structure. This method to fabricate high‐density memory devices could be used for memory cells that occupy large areas, and to overcome the scaling limit of existing methods; it also presents a way to use OHPs to increase memory storage capacity.     

Ferroelectricity and Antiferroelectricity of Doped Thin HfO2‐Based Films

The recent progress in ferroelectricity and antiferroelectricity in HfO₂‐based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O₃, BaTiO₃, and SrBi₂Ta₂O₉, which are considered to be feasible candidate materials for non‐volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si‐compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si‐doped HfO₂ thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro­electricity or antiferroelectricity in thin HfO₂ films. They have large remanent polarization of up to 45 μC cm^?2, and their coercive field (≈1–2 MV cm^?1) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin (<10 nm) and have a large bandgap (>5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field‐effect‐transistors and three‐dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid‐state‐cooling, and infrared sensors.     

Thermally Activated Delayed Fluorescence Materials Towards the Breakthrough of Organoelectronics

The design and characterization of thermally activated delayed fluorescence (TADF) materials for optoelectronic applications represents an active area of recent research in organoelectronics. Noble metal‐free TADF molecules offer unique optical and electronic properties arising from the efficient transition and interconversion between the lowest singlet (S₁) and triplet (T₁) excited states. Their ability to harvest triplet excitons for fluorescence through facilitated reverse intersystem crossing (T₁→S₁) could directly impact their properties and performances, which is attractive for a wide variety of low‐cost optoelectronic devices. TADF‐based organic light‐emitting diodes, oxygen, and temperature sensors show significantly upgraded device performances that are comparable to the ones of traditional rare‐metal complexes. Here we present an overview of the quick development in TADF mechanisms, materials, and applications. Fundamental principles on design strategies of TADF materials and the common relationship between the molecular structures and optoelectronic properties for diverse research topics and a survey of recent progress in the development of TADF materials, with a particular emphasis on their different types of metal‐organic complexes, D‐A molecules, and fullerenes, are highlighted. The success in the breakthrough of the theoretical and technical challenges that arise in developing high‐performance TADF materials may pave the way to shape the future of organoelectronics.     

II3V2 (II: Zn,Cd; V: P,As) Semiconductors: From Bulk Solids to Colloidal Nanocrystals

II₃V₂ semiconductors have become increasingly popular for a variety of applications including solar light harvesting, near‐IR imaging, and low energy light detection. The bulk physical and electronic structure of these materials is highlighted, followed by an in‐depth survey on progress in synthesizing these semiconductors as colloidal nanocrystals. Interestingly, no universal synthetic approach has yet been developed to access all compounds within this family. A discussion on how the complex crystal structure of these materials translates to small domain sizes will highlight current challenges in the characterization of II₃V₂ nanocrystals. Finally, potential avenues for further research will be proposed as a way to advance this field towards greater utilization in light harvesting applications.     

Magnetic Proximity Effect in Graphene/CrBr3 van der Waals Heterostructures

2D van der Waals heterostructures serve as a promising platform to exploit various physical phenomena in a diverse range of novel spintronic device applications. Efficient spin injection is the prerequisite for these devices. The recent discovery of magnetic 2D materials leads to the possibility of fully 2D van der Waals spintronics devices by implementing spin injection through the magnetic proximity effect (MPE). Here, the investigation of MPE in 2D graphene/CrBr₃ van der Waals heterostructures is reported, which is probed by the Zeeman spin Hall effect through non-local measurements. Quantitative estimation of the Zeeman splitting field demonstrates a significant MPE field even in a low magnetic field. Furthermore, the observed anomalous longitudinal resistance changes at the Dirac point R_XX,D with increasing magnetic field near ν = 0 may be attributed to the MPE-induced new ground state phases. This MPE revealed in the graphene/CrBr₃ van der Waals heterostructures therefore provides a solid physics basis and key functionality for next-generation 2D spin logic and memory devices.     

Patterning technology for solution-processed organic crystal field-effect transistors

Organic field-effect transistors (OFETs) are fundamental building blocks for various state-of-the-art electronic devices. Solution-processed organic crystals are appreciable materials for these applications because they facilitate large-scale, low-cost fabrication of devices with high performance. Patterning organic crystal transistors into well-defined geometric features is necessary to develop these crystals into practical semiconductors. This review provides an update on recentdevelopment in patterning technology for solution-processed organic crystals and their applications in field-effect transistors. Typical demonstrations are discussed and examined. In particular, our latest research progress on the spin-coating technique from mixture solutions is presented as a promising method to efficiently produce large organic semiconducting crystals on various substrates for high-performance OFETs. This solution-based process also has other excellent advantages, such as phase separation for self-assembled interfaces via one-step spin-coating, self-flattening of rough interfaces, and in situ purification that eliminates the impurity influences. Furthermore, recommendations for future perspectives are presented, and key issues for further development are discussed.     

Materials and Fabrication Needs for Low‐Cost Organic Transistor Circuits

There has been tremendous progress in the area of organic electronic materials and devices recently. However, many challenges and problems remain to be addressed for practical applications of such materials and devices. This article seeks to summarize some of the important recent materials‐related research on organic transistors and point out future needs in this area. Special emphasis is directed towards the stability and processability of the active materials.     

Mechanically Flexible Conductors for Stretchable and Wearable E‐Skin and E‐Textile Devices

Considerable progress in materials development and device integration for mechanically bendable and stretchable optoelectronics will broaden the application of “Internet‐of‐Things” concepts to a myriad of new applications. When addressing the needs associated with the human body, such as the detection of mechanical functions, monitoring of health parameters, and integration with human tissues, optoelectronic devices, interconnects/circuits enabling their functions, and the core passive components from which the whole system is built must sustain different degrees of mechanical stresses. Herein, the basic characteristics and performance of several of these devices are reported, particularly focusing on the conducting element constituting them. Among these devices, strain sensors of different types, energy storage elements, and power/energy storage and generators are included. Specifically, the advances during the past 3 years are reported, wherein mechanically flexible conducting elements are fabricated from (0D, 1D, and 2D) conducting nanomaterials from metals (e.g., Au nanoparticles, Ag flakes, Cu nanowires), carbon nanotubes/nanofibers, 2D conductors (e.g., graphene, MoS₂), metal oxides (e.g., Zn nanorods), and conducting polymers (e.g., poly(3,4‐ethylenedioxythiophene):poly(4‐styrene sulfonate), polyaniline) in combination with passive fibrotic and elastomeric materials enabling, after integration, the so‐called electronic skins and electronic textiles.     

Review of Applications of High-Temperature Superconductors

Since the discovery of high-T _c superconductor oxides in 1986, much research and development have been carried out, and much progress has been made. In the last ten years our efforts have been devoted to the development of materials technologies for these difficult materials, and remarkable progress has been made. This is a great contribution not only for application but also for fundamental research on high-T _c superconductors. In this paper, we will present a review of applications of high-T _c superconductors discovered in the last ten years. At present, it can be said that we are in the transition period from the period of growth to the period of specialization, looking for future applications of high-T _c superconductivity.     

Electron-Doping Mottronics in Strongly Correlated Perovskite

The discovery of hydrogen-induced electron localization and highly insulating states in d-band electron correlated perovskites has opened a new paradigm for exploring novel electronic phases of condensed matters and applications in emerging field-controlled electronic devices (e.g., Mottronics). Although a significant understanding of doping-tuned transport properties of single crystalline correlated materials exists, it has remained unclear how doping-controlled transport properties behave in the presence of planar defects. The discovery of an unexpected high-concentration doping effect in defective regions is reported for correlated nickelates. It enables electronic conductance by tuning the Fermi-level in Mott–Hubbard band and shaping the lower Hubbard band state into a partially filled configuration. Interface engineering and grain boundary designs are performed for H_xSmNiO₃/SrRuO₃ heterostructures, and a Mottronic device is achieved. The interfacial aggregation of hydrogen is controlled and quantified to establish its correlation with the electrical transport properties. The chemical bonding between the incorporated hydrogen with defective SmNiO₃ is further analyzed by the positron annihilation spectroscopy. The present work unveils new materials physics in correlated materials and suggests novel doping strategies for developing Mottronic and iontronic devices via hydrogen-doping-controlled orbital occupancy in perovskite heterostructures.     

Transparente Elektroden auf Kunststofffolien

Transparent electrodes have gained a considerable importance in various fields, like e.g. touchscreen devices. Future applications will require higher performance with regard to both electrical and optical properties and they will require lower cost. Today most electrodes are made of transparent conducting oxides like indium tin oxide (ITO). These materials can be sputtered from ceramic targets by dc sputtering processes with simple process control setups. Polymer films can be coated with these materials in vacuum roll coaters. These systems allow the sputtering processes to be run during an unwind‐rewind‐cycle of the roll. Sheet resistance values as low as 20 Ω_squ can be achieved by this technology. Lower resistance values require different approaches. A new and very effective solution is the superposition of the transparent oxide with a metal network. However, also approaches which completely base on organic materials are under investigation. These solutions benefit from the progress in organic conductors. They can be made without any vacuum coating technology. Besides the low sheet resistance also the mechanical robustness against bending is an important advantage of full‐organic approaches.     

Inorganic lead-based halide perovskites: From fundamental properties to photovoltaic applications

Compared with organic–inorganic hybrid halide perovskites (OIHPs), inorganic cesium lead halide perovskites (CsPbX₃) possess superior intrinsic stability for high temperatures and are considered one of the most attractive research hotspots in the perovskite photovoltaic (PV) field in the past several years. The PCE of CsPbX₃ inorganic perovskite solar cells (IPSCs) has increased from 2.9% in 2015 to more than 20% with excellent stability. There are still many on-going studies on the properties of perovskite materials and their applications in PV technology, thereby needing a thorough understanding. Here, the progress of inorganic perovskites is systematically introduced, including the fundamental properties of CsPbX₃ materials and CsPbX₃-based PV devices. The origins of stability and instability of CsPbX₃ and defects in CsPbX₃ are discussed. CsPbI₃-, CsPbI₂Br-, CsPbIBr₂- and CsPbBr₃-based PV devices and performance are comprehensively reviewed. The stabilization methods and mechanism for the photoactive phases of inorganic perovskites with low bandgap are emphasized. Reported strategies to boost the performance of CsPbX₃-based IPSCs are summarized. In the end, the potential of inorganic perovskites is evaluated, which opens up new prospects for the commercialization of IPSCs.     

ZnO薄膜的缺陷研究进展

ZnO是一种新型的Ⅱ-Ⅵ族半导体材料，具有许多优异的性能，可望成为新一代光电材料。但由于ZnO存在许多缺陷从而对它的各种性能产生了不良影响。比如点缺陷会影响ZnO的p型制备，Vo可能导致ZnO薄膜产生绿光；线缺陷可能成为载流子陷阱中心和复合中心，影响薄膜器件性能；层错会影响薄膜的能带结构从而影响其光电性能。为制备良好可靠的ZnO薄膜从而实现ZnO光电器件，必须研究ZnO薄膜的缺陷特性，文章对此进行了详细阐述．