有机双层薄膜器件界面限制传导温度特性研究

通过对器件的温度特性的研究,能够使器件在合适的温度下保持稳定的工作状态.本文以Miller-Abrahams跳跃传导理论为基础,建立了有机-有机界面限制电流传导的电荷传输的解析模型.依据此模型分析了结构为“注入电极/有机层Ⅰ/有机层Ⅱ/收集电极”的双层薄膜器件在有机界面限制电流传导状态下的电流、电场和载流子分布与工作温度的变化关系.结果表明,在给定的工作电压下,温度升高时降落在层Ⅰ的电压升高,电场增强,而降落在层Ⅱ的电压降低,电场减弱,同时器件的电流增大.     

有机双层薄膜器件界面限制传导温度特性研究

通过对器件的温度特性的研究,能够使器件在合适的温度下保持稳定的工作状态.本文以Miller-Abrahams跳跃传导理论为基础,建立了有机-有机界面限制电流传导的电荷传输的解析模型.依据此模型分析了结构为"注入电极/有机层Ⅰ/有机层Ⅱ/收集电极"的双层薄膜器件在有机界面限制电流传导状态下的电流、电场和载流子分布与工作温度的变化关系.结果表明,在给定的工作电压下,温度升高时降落在层Ⅰ的电压升高,电场增强,而降落在层Ⅱ的电压降低,电场减弱,同时器件的电流增大.     

壳层厚度对于量子点/聚合物复合电子存储器件性能的影响

研究了一种含有不同壳层结构量子点的聚乙烯咔唑(PVK)/Cd Se量子点复合体系电双稳器件,结果发现基于无壳层量子点的器件电荷存储能力较差,随着壳层厚度的增加,器件的电学特性由双稳态向三稳态转变。通过电容-电压(C-V)的测试结果表明,壳层的厚度对于量子点的电荷捕获能力有重要的影响,从而导致器件表现出不同的存储特性。     

利用PbS量子点波长转换膜实现近红外电致发光

采用聚合物poly(N-vinylcarbazole) (PVK)掺 杂小分子蓝色荧光材料 N,N′-bis(naphthalen-1-y)-N,N′-bis(phenyl) benzidine (NPB)作为蓝色发光层, 将PbS量子点与环氧树脂的混合 物涂覆在ITO导电玻璃背面作为波长转换膜,制备了结构为PbS QDs/Glass/ITO/PVK:NPB /Al的近红外波 长转换有机电致发光器件(OLED)。蓝色发光层中,NPB发出峰值位于445nm的蓝光。通过控制前驱体S/Pb比例调节PbS量 子点的粒径,正向电场下获得900～1600nm范 围可调节峰值的近红外光发射。经过优化波长转换膜中PbS量 子点比例,增强了波长转换膜对蓝光的吸收,当PbS量子点比例为10%左右时器件发射强 度最高。     

PMMA:C60存储器件制备及其电双稳特性

采用氯苯/三氯甲烷混合溶剂配制聚甲基丙烯酸甲酯(PMMA):富勒烯(C60)溶液,运用旋涂法以氧化铟锡为基底制备薄膜,运用原子力显微镜对薄膜表面形貌进行表征。制备了ITO/PMMA:C60/Al结构的有机双稳态器件,采用伏安法对器件的电双稳态性能进行测试。最后,分析了有机层中的电荷陷阱对器件电双稳特性的影响。实验表明,当溶剂体积比为1:1时,薄膜粗糙度较低,以此薄膜为功能层制备的器件阈值电压为5.4 V,高/低电阻态的电阻比值达到32.1。器件的阈值电压随着薄膜表面粗糙的增加而加大。     

基于电荷传输层优化的量子点发光二极管

采用溶液法旋涂薄膜、真空蒸镀铝电极,制备了ITO/PEDOT∶PSS/空穴传输材料/量子点/纳米氧化锌(ZnO Nanoparticles)/Al结构的量子点发光二极管(QLED)器件。对比了不同纳米氧化锌分散剂对器件性能的影响。当用乙醇和乙醇胺分散氧化锌时,对量子点层破坏较小,器件的亮度最高达22 940cd/m2,电流效率达28.9cd/A。研究了在聚乙烯咔唑(PVK)中掺杂不同比例4,4′-环己基二[N,N-二(4-甲基苯基)苯胺](TAPC)器件的发光特性。在PVK中掺杂TAPC材料能够促进器件空穴传输以及电子空穴注入平衡,当PVK∶TAPC=3∶1时,器件的空穴传输层形貌较为平整,亮度较高;当PVK∶TAPC=1∶1时,器件的开启电压最低。通过对器件膜层表面形貌以及电学、光学性能的对比,分析了电荷传输层优化对器件特性改善的原因。     

MoS_2纳米片的制备及其电双稳性能

利用简易的"一锅法"制备了正丁硫醇修饰的MoS_2纳米片(MoS_2-C_4),并对其结构、组分、形貌及电双稳性能进行了研究。正丁硫醇在反应过程中既作为硫源,又作为表面活性剂。X射线衍射(XRD)测试表明制备的样品为六方晶系的MoS_2。从透射电镜(TEM)和原子力显微镜(AFM)可以看出样品的形貌为片状,较大的纳米片是由较小的纳米片自组装而成。测试了样品的吸收光谱,由吸收峰的位置证明了合成的样品为2H-MoS_2纳米片。利用旋涂法将所制备的纳米片与聚乙烯基咔唑(PVK)的混合物制备了电双稳器件,通过电流-电压(I-V)测试证明了该器件具有很好的电双稳性能。     

PbS/并五苯场效应晶体管红外光电探测器

合成了尺寸均匀、分散性好,且吸收峰在近红外光谱区的硫化铅(PbS)量子点(QDs),并将其作为红外光吸收源与易于成膜且电学性能优良的有机化合物并五苯(Pentacene)相结合,形成量子点/并五苯复合薄膜作为有源层,采用顶栅底接触型水平场效应晶体管(FET)结构制备了红外光电探测器Au(S,D)/PbS QDs/Pentacene/PMMA/Al(G)。测试了暗态和980 nm波长激光照射下器件的电学参数和探测参数;探究了器件中载流子的传输机制;得到了电学和探测性能优良的PbS量子点/并五苯复合薄膜FET红外光电探测器,在辐照度为0.1 mW/cm2的红外激光照射下,器件的响应度达到49.4 mA/W,对应探测率为1.7×1011 Jones。     

用视频摄像技术测定纳米晶聚合物复合薄膜的传输损耗

研制了一种新的钛酸铅 聚醚醚酮 (PT PEK c)纳米晶聚合物复合薄膜 ,用视频摄像技术准确、实时地分析了这种复合薄膜的传输损耗。该方法包括一架高分辨率的数码相机和相应的数据处理软件 ,以及棱镜耦合系统 ,其测量范围为 0 5～ 10 0dB/cm ,用这种方法测得PT PEK c纳米晶聚合物复合薄膜在 6 33nm处的传输损耗为 3 0 9dB/cm。     

CdSe／PVK纳米晶薄膜及其电致发光特性

以巯基乙酸（RSH）为稳定剂，在水溶液中合成CdSe纳米晶，用表面活性剂将分散在水溶液中的纳米颗粒转移到有机溶剂中，与具有电荷输运性能的有机聚合材料复合。作为电致发光（EL）器件的工作层，得到较强的位于600nm附近的CdSe纳米晶的带边发射，以及较弱的位于420nm附近的来自聚合物的发射。器件EL强度首先随着外加电压的增加而增加，当电压超过26V时，EL强度开始下降。器件的电流-电压（I-V）特性基本符合二极管特性，表明器件是受载流子注入限制的。     

Electrical bistability,negative differential resistance and carrier transport in flexible organic memory device based on polymer bilayer structure

Bistable nonvolatile memory devices containing two different layers of polymers, viz. MEH-PPV (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenyl vinylene]) and PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) has been fabricated by a simple spin-coating technique on flexible polyimide (PI) substrates with a structure Al/MEH-PPV/PEDOT:PSS/Ag-Pd/PI. The current–voltage measurements of the as-fabricated devices showed a nonvolatile electrical bistability with electric field induced charge transfer through the polymer layers and negative differential resistance (NDR) which is attributed to the charge trapping in the MEH-PPV layer. The current ON/OFF ratio between the high-conducting state (ON state) and low-conducting state (OFF state) is found to be of the order of 10³ at room temperature which is comparable to organic field effect transistor based memory devices. We propose that such an improvement of rectification ratio (ON/OFF ratio) is caused due to the inclusion of PEDOT:PSS, which serves as a conducting current path for carrier transport; however, NDR is an effect of the trapped charges in the MEH-PPV electron confinement layer. The device shows excellent stability over 10⁴ s without any significant degradation under continuous readout testing in both the ON and OFF states. The carrier transport mechanism of the fabricated organic bistable device has been explained on the basis of different conduction mechanisms such as thermionic emission, space-charge-limited conduction, and Fowler–Nordheim tunneling. A band diagram is proposed to explain the charge transport phenomena. These bilayer structures are free from the drawbacks of the single organic layer based memory devices where the phase separation between the nanoparticles and polymers leads to the degradation of device stability and lifetime.     

Chemical linkage functions of poly(ether imide)s on the resistive switching memory effects

A series of aromatic poly(ether imide)s, AZTA-PEIs containing triphenylamine and 1,2,4-triazole moieties are prepared and characterized. All the polymers with inherent viscosity from 0.58 to 1.1 dL/g show glass transition temperatures in the range of 250–278 °C. Resistive switching memory devices are constructed based on the processable poly(ether imide) (AZTA-PEIa). The device can be switched from the initial OFF state to the ON state under either positive or negative electrical sweep at about ±3.2 V. The ON state is nonvolatile and can maintain the high conducting state even turning off the electrical power and applying a reverse bias. The device fulfills the requirements of a write-once read-many times memory (WORM) with a high ON/OFF current ratio up to 10⁵ and a long retention time in both ON and OFF states. The bistable switching effects of the polymer result from the conformation-coupled charge transfer from electron donors (triazole-substituted triphenylamine moieties) to electron acceptors (phthalimide moieties). By comparing with the memory behaviors of analogue polymers, the functions of ether and imide in the chemical polymer structure on the memory behaviors are discussed.     

Fabrication of Bistable Switching Memory Devices Utilizing Polymer–ZnO Nanocomposites

This work reports fabrication of bistable memory switching devices employing wet-chemically synthesized ZnO nanoparticles with polymethyl methacrylate and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] polymers. ZnO nanoparticle-embedded polymer layers were coated on conducting indium tin oxide (ITO) glasses using the spin-coating technique. Synthesized ZnO nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, energy-dispersive x-ray, and photoluminescence studies. These ZnO particles are 20?nm to 30?nm in size with hexagonal structure. Switching and memory effects of the devices fabricated employing the ZnO nanoparticle?Cpolymer composite films were investigated using current?Cvoltage (I?CV) characteristics. The I?CV measurements of both polymer devices showed electrical bistability. The ON to OFF current ratio of the bistable device was found to be ??10³. The observed current?Ctime response showed good memory retention behavior of the fabricated devices. The carrier transport mechanism of the devices has been described on the basis of I?CV experimental results and electronic structure.     

Memory stabilities and mechanisms of organic bistable devices with a phase-separated poly(methylmethacrylate)/poly(3-hexylthiophene) hybrid layer

Organic bistable devices (OBDs) with a poly(methylmethacrylate) (PMMA)/poly(3-hexylthiophene) (P3HT) hybrid layer, acting as a charge storage region, formed by using a vertical phase self-separation method were fabricated. The current–voltage curves of the Al/P3HT/PMMA/indium-tin-oxide devices exhibited current bistabilities with a maximum ON/OFF ratio of 1 × 10⁴. The write-read-erase-read sequence results demonstrated the switching characteristics of the OBDs. The cycling endurance number of the ON/OFF switching for the OBD was above 1 × 10⁵. The memory characteristics of the OBDs were attributed to trapping and detrapping processes of electrons into and out of the P3HT/PMMA heterointerfaces.     

Charge-transport characteristics in bistable resistive Poly(N-vinylcarbazole) films

Charge-transport characteristics of bistable resistive poly(N-vinylcarbazole) films as a function of temperature have been investigated. It is found that the on-state charge transport is dominated by ohmic conduction, hopping with an energy scale of the order of /spl sim/ 20 meV. The off-state charge transport appears to follow a transition from ohmic to space charge limited conduction with a shallow-trap distribution. Nonetheless, the poly(N-vinylcarbazole) (PVK) film does not possess its memory characteristics when operated at temperatures higher than 410 K. The PVK film can be operated at low voltage (< 2 V) with a high on/off current ratio as large as 10/sup 6/.     

Memory performance of a thin-film device based on a conjugated copolymer containing fluorene and chelated europium complex

A memory device based on the sandwiched structure of a conjugated copolymer (PF8Eu), containing fluorene and chelated europium complex, has been fabricated. An electrical bistability phenomenon was observed on this device: low conductivity state for the as-fabricated device and high conductivity state after device transition by applying a voltage of /spl sim/3 V. At the low conductivity state, the device showed a charge injection controlled current and at the high conductivity state, the device showed a space charge limited current. At the same applied voltage, the device exhibited two distinguishable conductivities with an ON/OFF current ratio as high as 10/sup 6/ at room temperature. After transition to the high conductivity state, the device tended to remain in the high conductivity state even when the applied voltage was removed. Thus, the device is a potential write-once-read-many-times memory device.     

Charge transport in lead sulfide quantum dots/phthalocyanines hybrid nanocomposites

A hybrid composite of non-aggregated lead sulfide (PbS) nanoparticles of average size 5.8 ± 1 nm embedded within a film of an octaalkyl substituted metal-free phthalocyanine (Compound 2) was prepared on interdigitated gold electrodes by mild acidic treatment of newly synthesised octasubstituted lead phthalocyanine analogue (Compound 1) in solid state phase. This nanocomposite film shows an enhancement of in-plane electrical conductivity over that of a film of octaalkyl substituted metal-free phthalocyanine alone by nearly 65%. This observation is consistent with the formation of charge complex compound as indicated by Raman and XPS data. The presence of PbS in the composite was examined on the basis of XRD peak positions which are comparable with those of bulk PbS. A band gap of 2.22 eV was calculated from optical absorption data using Tauc's law, implying quantum confinement. The mono dispersal behaviour of PbS nanoparticles was established from TEM and XRD studies. The hopping conduction mechanism is found to be primarily responsible for charge transport in the hybrid nanocomposite film with the hopping distance larger than PbS diameter.     

A Nonvolatile Organic Memory Device Using ITO Surfaces Modified by Ag‐Nanodots

We report on a single‐layer organic memory device made of poly(N‐vinylcarbazole) embedded between an Al electrode and ITO modified with Ag nanodots (Ag‐NDs). Devices exhibit high ON/OFF switching ratios of 10⁴. This level of performance could be achieved by modifying the ITO electrodes with some Ag‐NDs that act as trapping sites, reducing the current in the OFF state. Temperature dependence of the electrical characteristics suggest that the current of the low‐resistance state can be attributed to Schottky charge tunnelling through low‐resistance pathways of Al particles in the polymer layer and that the high‐resistance state can be controlled by charge trapping by the Al particles and Ag‐NDs.     

Highly-reproducible nonvolatile memristive devices based on polyvinylpyrrolidone: Graphene quantum-dot nanocomposites

The properties of nonvolatile memristive devices (NMD) fabricated utilizing organic/inorganic hybrid nanocomposites were investigated due to their superior advantages such as mechanical flexibility, low cost, low-power consumption, simple technological process in fabrication and high reproducibility. The current-voltage (I-V) curves for the Al/polyvinylpyrrolidone (PVP): graphene quantum-dot (GQD)/indium-tin-oxide (ITO) memristive devices showed current bistability characteristics at 300 K. The window margins corresponding to the high-conductivity (ON) state and the low-conductivity (OFF) state of the devices increased with increasing concentration of the GQDs. The ON/OFF ratio of the optimized device was 1 × 10⁴, which was the largest memory margin among the devices fabricated in this research. The endurance number of ON/OFF switching was above 1 × 10² cycles, and the retention time was relatively constant, maintaining a value above 10⁴ s. The devices showed high reproducibility with the writing voltage being distributed between −0.5 and −1.5 V and the erasing voltage being distributed between 2 and 3 V. The ON state currents remained between 0.02 and 0.03 A, and the OFF state currents stayed between 10⁻⁶ and 10⁻⁴ A. The carrier transport mechanisms are illustrated by using both the results obtained by fitting the I-V curves and the energy band diagrams of the devices.