A donor-acceptor structured conjugated copolymer for flexible memory device

A Donor-Acceptor structured conjugated copolymer PCNCzF was designed and synthesized for flexible polymer memory. The fabricated Al/PCNCzF/ITO-coated PET device exhibited non-volatile WORM memory effect, with the switch-on threshold voltage of −1.4 V, and an ON/OFF current ratio of more than 10⁴. The reliability and mechanical stability of the flexible memory device was deduced from the endurance and bending tests. Theoretical simulation, in-situ fluorescence spectra, as well as C-AFM measurements were employed to evaluate the switching mechanism of the memory device. The present flexible memory device was expected to meet the demand for flexible electronics applications.     

Multiple Functionalization of Mesoporous Silica in One‐Pot: Direct Synthesis of Aluminum‐Containing Plugged SBA‐15 from Aqueous Nitrate Solutions

Aluminum‐containing plugged mesoporous silica has been successfully prepared in an aqueous solution that contains triblock copolymer templates, nitrates, and silica sources but without using mineral acid. The acidity of the solution can be finely tuned from pH 1.4 to 2.8 according to the amount of the introduced aluminum species which ranged from an Al/Si molar ratio of 0.25/1 to 4.0/1. The aluminum nitrate additive in the starting mixture, along with the weak acidity produced by the nitrates, contributes to the formation of plugged hexagonal structures and the introduction of different amounts of aluminum species into the mesostructure. Characterization by X‐ray diffraction, transmission electron microscopy, and N₂ sorption measurements show that the Al‐containing plugged silicas possess well‐ordered hexagonal mesostructures with high surface areas (700–860 m² g^–1), large pore volume (0.77–1.05 cm³ g^–1) and, more importantly, combined micropores and/or small mesopores in the cylindrical channels. Inductively coupled plasma–atomic emission spectrometry results show that 0.7–3.0 wt % aluminum can be introduced into the final samples. ²⁷Al MAS NMR results display that about 43–60% aluminum species are incorporated into the skeleton of the Al‐containing silicas and the amount of the framework aluminum increases as the initial added nitrates rises. Scanning electron microscopy images reveal that the directly synthesized Al‐containing plugged silica has a similar morphology to that of traditional SBA‐15. Furthermore, the Al‐containing plugged samples have excellent performances in the adsorption and the catalytic decomposition of isopropyl alcohol and nitrosamine. Finally, the direct synthesis method is used to produce plugged mesoporous silicas that contain other metals such as chromium and copper, and the resultant samples also show good catalytic activities.     

MgO-Y_2O_3对热压烧结Al_2O_3性能的影响

以高纯的硫酸铝氨分解的无定形Al2O3为原料,MgO-Y2O3为烧结助剂,在N2气氛下热压烧结制备Al2O3陶瓷。研究了烧结助剂掺量对Al2O3材料的相组成、显微结构、烧结性能、力学性能、热导率和介电性能的影响。结果表明:所制Al2O3陶瓷具有细晶的显微结构特征和超高的抗弯强度。随着MgO-Y2O3掺量的增加,晶粒尺寸、抗弯强度和热导率先增大后减小,而介电损耗则呈现先减小后增大的变化规律。当MgO和Y2O3掺量均为质量分数2%时,Al2O3陶瓷呈现为较佳的综合性能:抗弯强度达最大值为603 MPa,热导率为36.47 W.m–1.K–1,介电损耗低至6.32×10–4。     

Interfacial microstructures and glass strengthening in anodic-bonded Al sheet/glass and sputtered Al film/glass

Two anodic bond interfaces were fabricated at 300 °C, between glass and either an Al sheet or a sputter-deposited Al film, and their microstructures and bending strengths were comparatively studied. In the Al sheet/glass interface, numerous local intrusions of crystalline Al₂O₃ with a long (100–350 nm) dendritic structure were formed in the glass adjacent to the aluminum. However, in the sputter-deposited Al film/glass interface, a continuous, thin (∼30 nm) amorphous layer with Al-oxide nanocrystals along the interface was present without the formation of dendrites after anodic bonding. The dendritic structures in the Al sheet/glass are attributed to an electrostatic instability imposed by the roughness and local oxidation of the Al sheet surface or, presumably, by microheating via gas discharge at the interface. The bending fracture strength for both types of bonded glasses increased by approximately 1.7 times compared with that of the bare glass due to the interfacial reaction.     

Polymer-Protected Cu-Ag Mixed NPs for Low-Temperature Bonding Application

A simple method has been proposed to prepare polymer-protected Cu-Ag mixed nanoparticles (NPs), which are suitable for use as low-temperature bonding materials. The polymer coated on the Cu-Ag mixed NPs can protect them from oxidation effectively when heated in air at temperature lower than 280°C. The low-temperature bonding process utilizing Cu-Ag mixed NPs as the bonding material is investigated. The bonding experiments show that robust joints are formed using Cu-Ag mixed NPs at 160°C in air. The shear test shows that addition of copper to silver is helpful for improving joint strength. This novel sintering-bonding technology using Cu-Ag mixed NPs as an interconnection material has potential for application in the electronics packaging industry.     

Polyelectrolyte Dielectrics for Flexible Low‐Voltage Organic Thin‐Film Transistors in Highly Sensitive Pressure Sensing

Organic thin‐film transistors (OTFTs) can provide an effective platform to develop flexible pressure sensors in wearable electronics due to their good signal amplification function. However, it is particularly difficult to realize OTFT‐based pressure sensors with both low‐voltage operation and high sensitivity. Here, controllable polyelectrolyte composites based on poly(ethylene glycol) (PEG) and polyacrylic acid (PAA) are developed as a type of high‐capacitance dielectrics for flexible OTFTs and ultrasensitive pressure sensors with sub‐1 V operation. Flexible OTFTs using the PAA:PEG dielectrics show good universality and greatly enhanced electrical performance under a much smaller operating voltage of ?0.7 V than those with a pristine PAA dielectric. The low‐voltage OTFTs also exhibit excellent flexibility and bending stability under various bending radii and long cycles. Flexible OTFT‐based pressure sensors with low‐voltage operation and superhigh sensitivity are demonstrated by using a suspended semiconductor/dielectric/gate structure in combination with the PAA:PEG dielectric. The sensors deliver a record high sensitivity of 452.7 kPa^?1 under a low‐voltage of ?0.7 V, and excellent operating stability over 5000 cycles. The OTFT sensors can be built into a wearable sensor array for spatial pressure mapping, which shows a bright potential in flexible electronics such as wearable devices and smart skins.     

Influence of electrical field dependent depletion at metal–polymer junctions on resistive switching of poly(N-vinylcarbazole) (PVK)-based memory devices

Polymer memory devices using Au nanoparticles (Au NPs) incorporated poly(N-vinylcarbazole) (PVK) as the active layer and Al films as the electrodes are investigated. The Al/PVK:Au NPs/Al devices exhibit electrical bistability in the I–V characteristics and show a conductance difference ratio between the high-resistance state (HRS) and low-resistance state (LRS) by a factor of 10⁵. Furthermore, the Au nanoparticle/PVK hybrid memory device can be programmed and exhibits excellent thermal stability up to 154 °C in ambient atmosphere. The current conduction is dominated by Schottky emission at HRS and exhibits Ohmic behavior at LRS. The dependence of the current conduction on temperature reveals the connection between the conduction character and the energy-band offsets at the metal (Al or Au)–PVK junctions. In addition, the resistive switching is correlated with the width of depletion region in PVK, which varies with the change of hole carrier concentration upon applying electrical field.     

Polymer Electronics Systems - Polytronics

Current trends in the development of electronics systems show that the provision of thin flexible components and semiconductors plays a decisive role in the steadily progressing development of highly integrated systems. A new generation of thin flexible electronic systems arises. At Fraunhofer IZM, inline manufacturing processes for polymer electronic systems are developed on production type equipment. A low-cost process for the fabrication of polymer electronics has been developed performed completely on continuous flexible foil substrates with typical thickness of 50 /spl mu/m, enabling low-functional electronic circuit fabrication with IC complexity up to 30 devices at present (2005). This process opens further possibilities to integrate thin silicon circuits and plastic microelectromechanical systems (MEMS) structures in the same fabrication and process environment. Microsystems incorporating fluidic, mechanical, optical, and electrical components are under research and development at present. Key applications scenarios for the polymer electronics predict fully applicable displays, embedded MEMS, labels for broad-band wireless communication, polymer batteries, and photovoltaic cells.     

Highly Flexible Organic Nanofiber Phototransistors Fabricated on a Textile Composite for Wearable Photosensors

Highly flexible organic nanofiber phototransistors are fabricated on a highly flexible poly(ethylene terephthalate) (PET) textile/poly(dimethylsiloxane) (PDMS) composite substrate. Organic nanofibers are obtained by electrospinning, using a mixture of poly(3,3^″′‐didodecylquarterthiophene) (PQT‐12) and poly(ethylene oxide) (PEO) as the semiconducting polymer and processing aid, respectively. PDMS is used as both a buffer layer for flattening the PET textile and a dielectric layer in the bottom‐gate bottom‐contact device configuration. PQT‐12:PEO nanofibers can be well‐aligned on the textile composite substrate by electrospinning onto a rotating drum collector. The nanofiber phototransistors fabricated on the PET/PDMS textile composite substrate show highly stable device performance (on‐current retention up to 82.3 (±6.7)%) under extreme bending conditions, with a bending radius down to 0.75 mm and repeated tests over 1000 cycles, while those prepared on film‐type PET and PDMS‐only substrates exhibit much poorer performances. The photoresponsive behaviors of PQT‐12:PEO nanofiber phototransistors have been investigated under light irradiation with different wavelengths. The maximum photoresponsivity, photocurrent/dark‐current ratio, and external quantum efficiency under blue light illumination were 930 mA W^?1, 2.76, and 246%, respectively. Furthermore, highly flexible 10 × 10 photosensor arrays have been fabricated which are able to detect incident photonic signals with high resolution. The flexible photosensors described herein have high potential for applications as wearable photosensors.     

Conjugated Polyelectrolyte Hybridized ZnO Nanoparticles as a Cathode Interfacial Layer for Efficient Polymer Light‐Emitting Diodes

Alkoxy side‐chain tethered polyfluorene conjugated polyelectrolyte (CPE), poly[(9,9‐bis((8‐(3‐methyl‐1‐imidazolium)octyl)‐2,7‐fluorene)‐alt‐(9,9‐bis(2‐(2‐methoxyethoxy)ethyl)‐fluorene)] dibromide (F8imFO₄), is utilized to obtain CPE‐hybridized ZnO nanoparticles (NPs) (CPE:ZnO hybrid NPs). The surface defects of ZnO NPs are passivated through coordination interactions with the oxygen atoms of alkoxy side‐chains and the bromide anions of ionic pendent groups from F8imFO₄ to the oxygen vacancies of ZnO NPs, and thereby the fluorescence quenching at the interface of yellow‐emitting poly(p‐phenylene vinylene)/CPE:ZnO hybrid NPs is significantly reduced at the CPE concentration of 4.5 wt%. Yellow‐emitting polymer light‐emitting diodes (PLEDs) with CPE(4.5 wt%):ZnO hybrid NPs as a cathode interfacial layer show the highest device efficiencies of 11.7 cd A^?1 at 5.2 V and 8.6 lm W^?1 at 3.8 V compared to the ZnO NP only (4.8 cd A^?1 at 7 V and 2.2 lm W^?1 at 6.6 V) or CPE only (7.3 cd A^?1 at 5.2 V and 4.9 lm W^?1 at 4.2 V) devices. The results suggest here that the CPE:ZnO hybrid NPs has a great potential to improve the device performance of organic electronics.     

柔性衬底黄光有机小分子电致发光器件

彩溅射技术在透明的塑性材料聚对苯二甲酸乙二酯（ＰＥＴ）薄膜之上形成一层ＩＴＯ导电膜,并对此替代常用的玻璃衬底制备了黄光柔性衬底有机小分子电致发光器件的结构为ＰＥＴ／ＩＴＯ／Ａ１ｑ３：Ｒｕｂ／Ａ１ｑ３／Ａ１。器件在１４Ｖ时亮度为１２０ｃｄ／ｍ＾２,并且器件在弯曲较大角度时仍然能正常使用,达到了使用柔性衬底的目的。     

Mechanical modeling of flexible OLED devices

General expressions are deduced for the stresses developed in the individual thin layers of a multi-layer structure as a result of bending to a specified radius. These are appropriate for analysing flexible organic light emitting diode (FOLED) devices on flexible substrates. Residual stress (caused internally by temperature change and differential thermal expansion) after material deposition and return to ambient temperatures is not considered. The reduced elastic modulus of the typical small molecule OLED materials: N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPD) and tris-(8-hydroxyquinoline)aluminum (Alq₃) are measured as thin-films using nano-indentation techniques. A conventional device: polyethylene terephthalate (PET)/Buffer layer (BL)/ITO/OLED/Al is considered from a modeling standpoint, as a preliminary to actual fabrication and subsequent comparative testing of OLED performance on rigid and flexible supports.     

Photoabsorption analysis of metal nanoparticles by hybrid quantum/classical scheme

The hybrid quantum/classical scheme (HQCS) is used for the photoabsorption analysis of metal nanoparticles. The HQCS divides the structure of interest into quantum and classical subsystems. First, we calculate and report Lorentz parameters for gold (Au), silver (Ag), aluminum (Al), chromium (Cr), and nickel (Ni) permittivities used in the classical subsystem. Then, photoabsorption spectra were obtained from HQCS for the single nanoparticle structures with and without two sodium (Na) atoms. The Au, Ag, Al, Cr, and Ni show strong sensitivity to the presence of the atomic subsystem. This work could pave the way for how coupled plasmon modes between metal nanoparticles and atomic structures can be utilized for sensing devices.     

Electrical switching and conduction mechanisms of nonvolatile write-once-read-many-times memory devices with ZnO nanoparticles embedded in polyvinylpyrrolidone

We reported on the influence of zinc oxide nanoparticles (ZnO NPs) on the electrical bistable behavior of nonvolatile write-once-read-many-times (WORM) memory devices based on an indium-tin oxide/polyvinylpyrrolidone (PVP):ZnO NPs/aluminum (ITO/PVP:ZnO/Al) structure. The maximum ON/OFF current ratio of the nonvolatile WORM memory devices was approximately 3 × 10³ and the devices remained in the ON state even after the applied voltage was turned off. In addition, reliability studies for response time and once write/continuous read operations of the optimal ZnO NPs concentration are presented. The response times of both rise-time and fall-time were about 3 and 6 μs respectively. The conduction mechanisms of all voltage regions of the device were analyzed by theoretical models and electron trapping in the ZnO NPs of the electron tunneling among a PVP matrix was discussed.     

All‐Plastic‐Materials Based Self‐Charging Power System Composed of Triboelectric Nanogenerators and Supercapacitors

Triboelectric nanogenerators (TENG) are a possible power source for wearable electronics, but the conventional electrode materials for TENG are metals such as Cu and Al that are easy to be oxidized or corroded in some harsh environments. In this paper, metal electrode material is replaced by an electrical conducting polymer, polypyrrole (PPy), for the first time. Moreover, by utilizing PPy with micro/nanostructured surface as the triboelectric layer, the charge density generated is significantly improved, more superior to that of TENG with metals as the triboelectric layer. As this polymer‐based TENG is further integrated with PPy‐based supercapacitors, an all‐plastic‐materials based self‐charging power system is built to provide sustainable power with excellent long cycling life. Since the environmental friendly materials are adopted and the facile electrochemical deposition technique is applied, the new self‐charging power system can be a practical and low cost power solution for many applications.     

In-situ synthesis of metal nanoparticle-polymer composites and their application as efficient interfacial materials for both polymer and planar heterojunction perovskite solar cells

A new approach for the synthesis of gold nanoparticles (Au NPs) via a simple and fast in-situ generation method using an amine-containing polymer (PN4N) as both stabilizer and reducing agent is reported. The application of the Au NPs-PN4N hybrid material as efficient interfacial layer in different types of solar cells was also explored. The synthesized Au NPs show good uniformity in size and shape and the Au NPs doped PN4N hybrid composites exhibit high stability. Amine-containing polymers are good cathode interfacial materials (CIMs) in polymer solar cells (PSCs) and planar heterojunction perovskite solar cells (PVKSCs). The performance of the PSCs with Au NPs doped PN4N CIMs is largely improved when compares to devices with pristine PN4N CIM due to the enhanced electronic properties of the doped PN4N. Furthermore, by incorporating larger Au NPs into PEDOT:PSS to enhance absorption of the light harvesting layer, power conversion efficiencies (PCEs) of 6.82% and 13.7% are achieved for PSC with PCDTBT/PC₇₁BM as the light harvesting materials and PVKSC with a ∼280 nm-thick CH₃NH₃PbI_3−xCl_x perovskite layer, respectively. These results indicate that Au NPs doped into both PEDOT:PSS and PN4N interlayers exhibited a synergistic effect in performance improvement of PSCs and PVKSCs.     

Biocompatible D–A Semiconducting Polymer Nanoparticle with Light‐Harvesting Unit for Highly Effective Photoacoustic Imaging Guided Photothermal Therapy

The development of nanotheranostic agents that integrate diagnosis and therapy for effective personalized precision medicine has obtained tremendous attention in the past few decades. In this report, biocompatible electron donor–acceptor conjugated semiconducting polymer nanoparticles (PPor‐PEG NPs) with light‐harvesting unit is prepared and developed for highly effective photoacoustic imaging guided photothermal therapy. To the best of our knowledge, it is the first time that the concept of light‐harvesting unit is exploited for enhancing the photoacoustic signal and photothermal energy conversion in polymer‐based theranostic agent. Combined with additional merits including donor–acceptor pair to favor electron transfer and fluorescence quenching effect after NP formation, the photothermal conversion efficiency of the PPor‐PEG NPs is determined to be 62.3%, which is the highest value among reported polymer NPs. Moreover, the as‐prepared PPor‐PEG NP not only exhibits a remarkable cell‐killing ability but also achieves 100% tumor elimination, demonstrating its excellent photothermal therapeutic efficacy. Finally, the as‐prepared water‐dispersible PPor‐PEG NPs show good biocompatibility and biosafety, making them a promising candidate for future clinical applications in cancer theranostics.     

High‐Performance All‐Polymer White‐Light‐Emitting Diodes Using Polyfluorene Containing Phosphonate Groups as an Efficient Electron‐Injection Layer

We report an efficient non‐doped all‐polymer polymer white‐light‐emitting diode (PWLED) with a fluorescent three‐color, white single polymer as an emissive layer, an ethanol‐soluble phosphonate‐functionalized polyfluorene (PF‐EP) as an electron‐injection/electron‐transport layer, and LiF/Al as a cathode, respectively. The all‐polymer PWLED achieves a peak external quantum efficiency of 6.7%, a forward viewing luminous efficiency of 15.4 cd A^?1 and a power efficiency of 11.4 lm W^?1, respectively, at a brightness of 347 cd m^?2 with Commission Internationale d’Eclairage coordinates of (0.37, 0.42) and color rendering index of 85, which is the best results among the non‐doped PWLEDs. Moreover, this kind of PWLED not only shows excellent color stability, but also achieves high brightness at low voltages. The brightness reaches 1000, 10000, and 46830 cd m^?2 at voltages of 4.5, 5.4, and 7.5 V, respectively. The significant enhancement of white‐single‐polymer‐based PWLEDs with PF‐EP/LiF/Al to replace for the commonly used Ca/Al cathode is attributed to the more efficient electron injection at PF‐EP/LiF/Al interfaces, and the coordinated protecting effect of PF‐EP from diffusion of Al atoms into the emissive layer and exciton‐quenching near cathode interfaces. The developed highly efficient non‐doped all‐polymer PWLEDs are well suitable for solution‐processing technology and provide a huge potential of low‐cost large‐area manufacturing for PWLEDs.     

A Ligand Exchange Route to Highly Luminescent Surface‐Functionalized ZnS Nanoparticles and Their Transparent Polymer Nanocomposites

A facile ligand exchange approach for surface‐functionalized ZnS nanoparticles (NPs) with 5‐(2‐methacryloylethyloxymethyl)‐8‐quinolinol (MQ) is described. The MQ–ZnS NPs, with a cubic crystal structure, have the same diameter as ZnS NPs without MQ about 3.0 nm. The MQ–ZnS NPs exhibit strong fluorescence emission at about 500 nm and a high photoluminescence (PL) quantum yield (QY), up to 40%, with a decreasing ratio of MQ to ZnS NPs. The PL decay study reveals that the lifetimes of the different MQ–ZnS NPs with a single exponential decay are in the nanosecond time domain for emission at about 500 nm, which is obviously different from that of ZnS NPs with a biexponential decay for defect‐state emission at 420 nm. The functionalized MQ–ZnS NPs are successfully incorporated into the polymer matrix by in situ bulk polymerization to fabricate transparent bulk nanocomposites with good thermal stability and processability. Transmission electron microscopy results show that the NPs are uniformly dispersed in the polymer matrix without aggregation. The good PL properties of MQ–ZnS NPs are preserved in the bulk nanocomposites. It is observed that the nanocomposites have red‐shifted excitation and emission wavelengths compared with those of both the polymer matrix and MQ–ZnS NPs, possibly because of the cooperative interaction between MQ–ZnS NPs and the polymer matrix with blue emission.