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.     

有机电致发光器件发光层中电场与载流子浓度分布的数值研究

以陷阱电荷限制传导理论为基础,用数值方法研究了单层有机电致发光器件发光层中电势、电场和载流子密度的空间分布.分析结果表明,电场强度在靠近两边电极的地方上升很快,而在中间区域几乎是线性地缓慢增大.大部分载流子分布在靠近两个电极的地方,只有少量分布在中间区域.在靠近注入电极的地方扩散电流大于漂移电流,而在其它区域漂移电流大于扩散电流.     

有机电致发光器件发光层中电场与载流子浓度分布的数值研究

以陷阱电荷限制传导理论为基础 ,用数值方法研究了单层有机电致发光器件发光层中电势、电场和载流子密度的空间分布 .分析结果表明 ,电场强度在靠近两边电极的地方上升很快 ,而在中间区域几乎是线性地缓慢增大 .大部分载流子分布在靠近两个电极的地方 ,只有少量分布在中间区域 .在靠近注入电极的地方扩散电流大于漂移电流 ,而在其它区域漂移电流大于扩散电流.     

基于PVK/PbS纳米晶有机无机复合薄膜电双稳器件性能研究

通过简单旋涂方法,制备了一种基于硫化铅（PbS）纳米晶与聚乙烯基咔唑（PVK）的有机/无机复合薄膜电双稳器件,并对所制备的器件进行性能测试及其电荷传输机制研究。首先采用热注入的方法制备了尺寸均一的立方形PbS纳米晶,然后将PbS纳米晶与PVK聚合物混合作为活性层材料,制备了有机/无机复合薄膜电双稳器件。该器件展示了良好的电双稳特性并且可以实现稳定的“读-写-读-擦”操作。器件的最大电流开关比能够达到10⁴。并进一步对器件在正向电压下的I-V曲线进行了理论拟合,发现在不同电流传导状态下,器件符合不同的电传导模型。进而分析了该电双稳器件中的电荷传输机制,认为在电场的作用下,发生在纳米晶与聚合物之间的电场诱导电荷转移是产生电双稳特性的主要原因。     

单层有机电致发光器件的电流 传导机制的数值拟合分析

采用真空蒸镀的方法制备了以八羟基喹啉铝(Alq₃)为功能层的单层同质结有机电致发光器件,器件结构为indium-tin-oxide(ITO)/tris-(8-hydroxylquinoline)-aluminum(Alq₃)(x nm)/Mg:Ag.通过改变有机功能层的厚度,采用陷阱电荷限制电流(TCLC)理论对器件电流的数值拟合方法具体地研究了不同薄膜厚度的有机半导体器件内部电流的传导机制,验证了实验结果和理论推导的一致性.结果表明,Alq₃层厚度较低的单层器件随外加电压增大,器件电流经历了从欧姆电导区、TCLC区到TCLC-空间电荷限制电流(SCLC)过渡区三个区域的变化;而对于Alq₃层厚度较高的单层器件,Alq₃层中的陷阱机构增多,导致电流－电压曲线的SCLC区域消失.     

酞菁铜缓冲层对有机太阳能电池开路电压的影响

用p型有机半导体材料酞菁铜作为阴极缓冲层制作了器件结构为氧化铟锡/酞菁锌/碳六十/酞菁铜/铝的有机小分子太阳能电池, 对器件进行电学测量发现酞菁铜缓冲层的厚度对器件的开路电压有明显影响.基于半导体器件物理分析了光照下测量得到的电流-电压曲线, 由拟合结果得到的器件参数表明高理想因子导致了器件开路电压升高, 其原因为器件的输运特性不只受酞菁锌与碳六十形成的p-n结影响, 还与酞菁铜缓冲层与铝电极形成的肖特基接触有关.研究表明在有机太阳能电池器件中引入一个合适的缓冲层/阴极肖特基结可以提高器件的开路电压.     

酞菁铜缓冲层对有机太阳能电池开路电压的影响（英文）

用p型有机半导体材料酞菁铜作为阴极缓冲层制作了器件结构为氧化铟锡/酞菁锌/碳六十/酞菁铜/铝的有机小分子太阳能电池,对器件进行电学测量发现酞菁铜缓冲层的厚度对器件的开路电压有明显影响.基于半导体器件物理分析了光照下测量得到的电流-电压曲线,由拟合结果得到的器件参数表明高理想因子导致了器件开路电压升高,其原因为器件的输运特性不只受酞菁锌与碳六十形成的p-n结影响,还与酞菁铜缓冲层与铝电极形成的肖特基接触有关.研究表明在有机太阳能电池器件中引入一个合适的缓冲层/阴极肖特基结可以提高器件的开路电压.     

有机电致发光器件中复合发光的电场和温度关系

通过分析有机电致发光器件中载流子注入、输运、激子的解离与复合过程，提出了激子解离与复合的理论模型。基于电流连续性方程和Poisson方程，给出了激子复合几率、电流密度及复合效率表达式。研究了外加电压和温度对器件中激子的复合几率及在各种接触条件下外加电压对器件电流和复合效率的影响。结果表明：(1)在一个较宽的注入势垒范围内，复合几率随电场和温度的升高而降低；(2)固定阴极势垒，而阳极势垒由小变大时，器件电流由接触限制向空间电荷限制转变；(3)复合效率随外加电压升高先增加，当电压达一临界值时而陡降，并存在一个最佳的注入势垒值。其计算值与所报道的实验结果相符合。     

一种有机薄膜器件的制备及电存储特性

研究了一种金属/有机物/金属夹层结构有机薄膜器件的可逆电双稳特性.器件的阳极和阴极分别为真空热蒸发沉积的Ag和Al薄膜,中间介质层为真空热蒸发沉积的2-(hexahydropyrimidin-2-ylidene)-malononitrile(HPYM)有机薄膜.器件起始状态为非导通态,在大气环境下,可用正、反向电场进行信号的写入和擦除,表现为极性记忆特性.通过自然氧化的方法在底电极Al表面形成一层Al2O3薄膜层后,可使器件在不同的正向电压脉冲作用下达到不同的导电态,具有一定的多重态存储特性.同时,研究了不同的电极组合对器件电性能的影响,并通过紫外-可见吸收光谱以及喇曼光谱对器件界面进行表征.     

一种有机薄膜器件的制备及电存储特性

研究了一种金属/有机物/金属夹层结构有机薄膜器件的可逆电双稳特性.器件的阳极和阴极分别为真空热蒸发沉积的Ag和Al薄膜,中间介质层为真空热蒸发沉积的2-(hexahydropyrimidin-2-ylidene)-malononitrile(HPYM)有机薄膜.器件起始状态为非导通态,在大气环境下,可用正、反向电场进行信号的写入和擦除,表现为极性记忆特性.通过自然氧化的方法在底电极Al表面形成一层Al2O3薄膜层后,可使器件在不同的正向电压脉冲作用下达到不同的导电态,具有一定的多重态存储特性.同时,研究了不同的电极组合对器件电性能的影响,并通过紫外-可见吸收光谱以及喇曼光谱对器件界面进行表征.     

有机电致发光器件Al电极表面形态变化的分析

制作了双层结构(ITO／TPD／AlQ／A1)的有机发光二极管(OLED)．并通过带有CCD相机的显微镜动态地观察了Al电极表面形态的变化。发现Al电极表面形态变化与工作时间及工作电压有关。在不同的工作时间与工作电压下．Al电极表面形态变化的程度也不一样。     

Fluorene bilayer for polymer organic light-emitting diode using efficient ionization method for atomized droplet

We present a solution-processed planar fluorene bilayer by an ultrasonic atomized deposition method in combination with a needle electrode as an ionization part for an atomized droplet. An important advantage of our method is that the atomized droplet is efficiently charged using a needle electrode, which speeds up the deposition rate of the polymer thin film. The deposition rate increases 2 to 3 times compared to a that obtained with a conventional technique without using the ionization method, and real-time monitoring of landed droplets indicates that the number of droplets increased as the voltage applied to the needle electrode was increased, owing to the highly charged atomized droplets. Furthermore, the TFB/F8BT bilayer was achieved by optimizing the substrate temperature, and the polymer organic light-emitting diode exhibits a luminance value exceeding 12,000 cd/m² by insertion of the TFB as an electron blocking layer. The maximum current efficiency of the fluorene bilayer device was 6.64 cd/A, which was a 3.2-fold increase compared to that obtained with the reference device without the TFB electron blocking layer.     

Modified PEDOT-PSS Conducting Polymer as S/D Electrodes for Device Performance Enhancement of P3HT TFTs

Poly(3,4-ethylenedioxythiophene)—Polystyrene Sulfonate (PEDOT-PSS) is the most widely used conducting polymer as electrode material in organic (polymer) devices. However, commercially available PEDOT-PSS in our experiment has a relatively low conductivity that reduces the device performance when it is used for electrode material. The purchased PEDOT-PSS has been mixed with polar solvent dimethyl sulfoxide, which increases its conductivity from 0.07 to 30 S/cm. The enhanced conductivity has long-term stability at room temperature and short-term stability at high temperature (100$^circ$C) in air ambient. The modified PEDOT-PSS has been inkjet printed and used as source/drain (S/D) electrodes for poly(3-hexylthiophene) (P3HT) thin-film transistors (TFTs). Unmodified PEDOT-PSS and gold have also been used as S/D electrodes for comparison. The TFTs with modified PEDOT-PSS electrodes show significantly improved performance over the devices with unmodified PEDOT-PSS electrodes and are similar to the devices with gold electrodes. The difference in device performance mainly results from parasitic series resistance. In the devices with unmodified PEDOTT-PSS, high electrode series resistance has several effects on devices, e.g., restricted current growth at high negative gate voltage, reduced on/off current ratio and current output capability.     

Understanding coupled electro-thermal processes in the catastrophic failure of organic electronic devices

The large-scale application of semiconducting polymers in organic electronics is hindered significantly by catastrophic device failure. Some of these processes are associated with coupled phenomena of electro-migration and thermal localization, which are poorly understood till date. In this paper we identify structural instability and its sources in a simple device configuration consisting of a semiconducting polymer sandwiched between two metal electrodes and subjected to various DC operating voltages. The coupled effect of temperature and electric fields leads to fracture of the polymer layer and the metal electrode layer, interestingly, in mutually exclusive regions. This failure is significantly observable beyond a certain applied voltage. It is observed that defects nucleate in a chain-like pattern with alternating fracture sites of polymer and metal electrode respectively. We subsequently propose a coupled electro-thermal mechanism which explains the observed phenomena. The mechanism is further validated by an analytical model of stress due to thermal and electric field distributions. The model predicts criteria of failure, which are interestingly complementary for the polymer and the electrode films, and hence explains the observation of the chain-like nucleation pattern. The failure criteria are functions of device geometry, operating voltage and temperature. This study will be useful toward reliability-based design of organic electronic devices including important factors such as coupled electro-thermal response and length-scale. The study also opens up important fundamental questions relating to the spatio-temporal evolution of electro-thermally induced minuscule electrical shorts in thin-film electronic devices.     

Light‐Emitting Field‐Effect Transistors Consisting of Bilayer‐Crystal Organic Semiconductors

A novel device structure for organic light‐emitting field‐effect transistors has been developed. The devices comprise bilayer‐crystal organic semiconductors of a p‐type and an n‐type. The pn‐junction can readily be formed by successively laminating two crystals on top of a gate insulator. This structure enables the efficient injection and transport of electrons and holes, leading to their effective recombination. As a result, bright emissions are attained. The devices are operated by AC gate voltages. Gate‐voltage phase‐resolved drain‐current and emission‐intensity measurements enable us to study the relationship between the emissions and carrier transport. The maximum external quantum efficiency reaches 0.045%.     

Low-Voltage Organic Field-Effect Transistor With PMMA/$ hbox{ZrO}_{2}$ Bilayer Dielectric

This paper reports on the application of a bilayer polymethylmethacrylate (PMMA)/ $hbox{ZrO}_{2}$ dielectric in copper phthalocyanine (CuPc) organic field-effect transistors (OFETs). By depositing a PMMA layer on $hbox{ZrO}_{2}$, the leakage of the dielectric is reduced by one order of magnitude compared to single-layer $hbox{ZrO}_{2}$. A high-quality interface is obtained between the organic semiconductor and the combined insulators. By integrating the advantages of polymer and high- $k$ dielectrics, the device achieves both high mobility and low threshold voltage. The typical field-effect mobility, threshold voltage, on/off current ratio, and subthreshold slope of OFETs with bilayer dielectric are $hbox{5.6}timeshbox{10}^{-2} hbox{cm}^{2}/hbox{V} cdot hbox{s}$, 0.8 V, $hbox{1.2} times hbox{10}^{3}$, and 2.1 V/dec, respectively. By using the bilayer dielectrics, the hysteresis observed in the devices with single-layer $hbox{ZrO}_{2}$ is no longer present.      

Organic thin-film field-effect transistors with MoO3/Al electrode and OTS/SiO2 bilayer gate insulator

An organic thin-film transistor (OTFTs) having OTS/SiO₂ bilayer gate insulator and MoO₃/Al electrode configuration between gate insulator and source–drain (S–D) electrodes has been investigated. Thermally grown SiO₂ layer is used as the OTFT gate dielectric and copper phthalocyanine (CuPc) for an active layer. We have found that using silane coupling agents, octadecyltrichlorosilane (OTS) on SiO₂, surface energy of SiO₂ gate dielectric is reduced; consequently, the device performance has been improved significantly. This OTS/SiO₂ bilayer gate insulator configuration increases the field-effect mobility, reduces the threshold voltage and improves the on/off ratios simultaneously. The device with MoO₃/Al electrode has similar source–drain current (I_DS) compared to the device with Au electrode at same gate voltage. Our results indicate that using double-layer of insulator and modified electrode is an effective way to improve OTFT performance.     

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.     

有机半导体薄膜三极管的研制

采用真空蒸镀法和有机半导体材料酞菁铜,制作Au/CuPc/Al/ CuPc/Au三明治结构的肖特基型栅极有机静电感应三极管.该三极管导电沟道垂直于CuPc薄膜,与采用MOSFET结构的有机薄膜三极管相比导电沟道大幅缩短,有利于克服有机半导体电学性能的缺点.实验结果表明,该三极管驱动电压低,呈不饱和电流-电压特性.其工作特性依赖于栅极电压和梳状铝电极的结构.通过合理设计、制作梳状铝电极,获得了良好的三极管静态、动态特性.