配向膜材料与面残影的关联性研究

利用mini-cell作为评价平台,从配向膜材料自身特性角度,对配向膜材料与面残影之间的关联性进行了综合研究。一方面,配向膜材料自身优异的稳定性有助于维持电压保持率(VHR);另一方面,配向膜材料自身的低电阻率特性有助于存储电荷的释放,利于实现较低的残余电流(RDC)。而当配向膜材料的RDC和高低温间VHR变化值同时处于较低水平时,可以获得面残影水平较低的TFT-LCD模块。因此,利用mini-cell对配向膜材料进行评估,通过比较RDC以及ΔVHR数值,可以间接实现对TFT-LCD的残影结果评估,为实际生产中产品残影的改善提供了基础理论指导,具有重要的指导性作用。     

TFT-LCD残像原理与分析-加强篇二

残像是TFT-LCD的一种显示特性,主要表现为当液晶显示器长时间显示同一个画面,在把画面切换到下一个画面时,原先的画面会残留在下一个画面中。本文的加强篇二从材料面的彩膜、液晶、配向膜及工艺面的配向膜工程、ODF工程导致的残像具体分析了其原因和改善方法。     

残影不良分析及改善对策研究

通过对大量残影不良样品进行分析,找到了残影不良产生的原因,并基于分析结果设计了改善残影的实验。通过分析发现:残影不良产生的原因是彩膜侧像素与黑矩阵之间的段差过大,在摩擦工程时段差过大区域形成了摩擦弱区,摩擦弱区内的液晶分子配向较弱,导致不良产生。为降低残影不良进行实验,结果显示:在彩膜侧加覆盖层可以有效降低残影不良的发生率,但不适用于量产;通过采用高预倾角的配向膜材料,同时控制配向膜工程到摩擦工程的时间,可使残影不良发生率由28.2%降低至0.2%,为企业的稳定高效生产奠定了基础。     

负性液晶在FFS模式下的残像研究

图像残像是评价画面质量的最重要因素之一,大部分工程师研究了组合物的材料和液晶面板的制造工艺,以改善影像残留,但之前的研究主要是以正性液晶材料为基础进行探讨的,本文主要以负性液晶材料为基础研究了用边缘场驱动的面板残像。首先为了比较正性液晶与负性液晶,测量了离子密度及电压保持率(VHR),其次为了比较两种配向材料(PI)与液晶材料的搭配特性并选择合适的组合,量测了样品的直流残留(RDC)电压和Vcom电压随时间的变化。从量测结果可知,紫外(UV)光照前负性液晶离子密度是正性液晶的39倍,经过紫外光照,后负性液晶的离子密度为560Pc/cm,且其紫外光照后电压保持率变化量为2.7%;使用负性液晶搭配PI1的样品A-1的直流残留电压和Vcom(等效为交流驱动电压的中心值)随时间变化量都是最大的,分别为0.5V和250mV,负性液晶搭配PI2材料的面板和正性液晶的面板的直流残留电压均小于0.2V,其Vcom随时间变化量均在50mV以内。负性液晶材料的离子浓度含量高,且其稳定性比正性液晶材料差,负性液晶材料比正性液晶材料更容易发生残像;对于使用负性液晶材料,边缘场驱动模式的面板,搭配PI2配向膜材料能够保持低的直流残留电压及低的Vcom电压变化量,从而对改善残像现象有帮助。     

自然螺距对扭曲向列相液晶显示器的影响

从理论上分析了自然螺距对常白模式扭曲向列相型液晶显示器响应时间及电光特性的影响,数值模拟了不同手性剂情况下扭曲液晶显示器的响应时间及电光特性。模拟结果表明:盒厚一定时,自然螺距越小,液晶显示器的响应时间越短,但是电光曲线陡度越缓,开态电压增大;扭曲角增大,响应时间变长,但是电光曲线陡度变大。综合考虑扭曲角和液晶的自然螺距,可以提高液晶显示器的显示特性。     

TFT-LCD残影不良的研究与改善

影像残留是TFT-LCD,特别是TN型产品常见的不良,对产品良率影响很大。本文从产品设计、工艺参数、工艺管控3个方面对残影进行分析。发现产品设计时Data线两侧段差过大,是导致残影发生的主要原因,通过增加配向膜厚度和摩擦强度值可以有效降低残影,实验得出配向膜膜厚高于110nm,摩擦强度高于5.5N·m时无残影发生。通过控制配向膜工程与摩擦工程间的延迟时间在5h,摩擦工程与对盒工程间的延迟时间在10h,并且严格管控ITO偏移量可以有效减少Panel内部电场,从而降低残影。通过以上措施,对于15.6HD产品,良率提升了10%,为企业高效生产奠定基础。     

膜补偿均匀排列向列相液晶盒(FHA-LCD)显示特性的研究

本文提出了一种可用于简单矩阵黑白显示的电控双折射液晶显示模式—膜补偿均匀平行排列液晶盒(FHA—LCD),它电服了传统的电控双折射均匀平行排列液晶盒没有阈值特性,显示时带有不期望的颜色的缺点,而又具有制作简单,成本低的特点。其对比度可达到20:1,文中从模拟计算和实验上讨论了液晶盒厚度,介电常数对电光特性陡度因子的影响。     

喷墨涂覆配向膜涂覆的质量优化

薄膜晶体管液晶显示器(TFT-LCD)成盒配向膜涂覆工艺中,配向膜的厚度、均一性和涂覆膜面质量直接影响液晶显示器的显示效果,为此本文研究了喷墨涂覆工艺对配向膜质量的影响。首先优化喷墨涂覆工艺,分析了喷吐频率对喷吐量及其均一性有显著影响。其次分析了负压、涂覆速度、配向膜溶液固含量、涂覆密度等条件对配向膜膜面质量的影响。实验表明当喷吐频率为1 000～8 000Hz时,喷吐量均一性满足要求;当吐出频率达到10 000Hz时,喷吐量严重不均一,不满足生产需求。得出喷涂频率、吐出量、负压、涂覆速度、配向膜溶液固含量、涂覆密度的优化条件分别为:3 000～5 000Hz、50～70pL、中心值±100Pa、500～600mm/s、(3.9±0.4)%、50%～50.3%。降低配向膜溶液固含量可改善涂覆性不均缺陷,改变吐出密度可改善涂覆性不均缺陷,画质质量得到提升。本文对成盒工段配向膜涂覆质量优化取得了良好效果,能满足工程实践量产的需要。     

基于使用负性液晶的边沿场切换模式的局部残影分析

随着液晶显示技术的发展,PPI越来越高,像素尺寸越来越小,穿透率的提升是一重要问题。负性液晶相对正性液晶具有高穿透率,较好的画面画质及较低的颜色偏差等优点,使得主流显示模式IPS、FFS使用负性液晶研究逐渐增多。但由于负性液晶自身特性,其影像残留较正性液晶更为严重,特别是模组粘合附近区域的局部面残。为了改善负性液晶局部影像残留,本文研究了实际样品影像残留严重区域与轻微区域不同测量数据,如温度、共电压(Vcom)等,发现影像残留严重区域与轻微区域的公共电压出现漂移现象,分析了影响残影的因素,并提出改善方案,实测结果证明本文改善局部残影的方法是有效的。     

液晶光阀特殊光电特性中的陡度随频率变化的分析

本文着重讨论了驱动频率对液晶光阀陡度因子的影响,由实验结果得出.当驱动频率为120Hz时,液晶光阀的陡度因子最小,显示信息容量最大;当小于120Hz时,显示不稳定;当大于120Hz时,陡度因子过大,影响显示容量.其结论将为设计液晶显示器件,提高其显示稳定性和显示信息容量提供依据,具有实际应用价值.     

Defect Modulation Doping

The doping of semiconductor materials is a fundamental part of modern technology, but the classical approaches have in many cases reached their limits both in regard to achievable charge carrier density as well as mobility. Modulation doping, a mechanism that exploits the energy band alignment at an interface between two materials to induce free charge carriers in one of them, is shown to circumvent the mobility restriction. Due to an alignment of doping limits by intrinsic defects, however, the carrier density limit cannot be lifted using this approach. Here, a novel doping strategy using defects in a wide bandgap material to dope the surface of a second semiconductor layer of dissimilar nature is presented. It is shown that by depositing an insulator on a semiconductor material, the conductivity of the layer stack can be increased by 7 orders of magnitude, without the necessity of high‐temperature processes or epitaxial growth. This approach has the potential to circumvent limits to both carrier mobility and density, opening up new possibilities in semiconductor device fabrication, particularly for the emerging field of oxide thin film electronics.     

Energy‐Level Alignment at the Organic/Electrode Interface in Organic Optoelectronic Devices

It is commonly believed that the work‐function reduction effect of the cathode interfacial material in organic electronic devices leads to better energy‐level alignment at the organic/electrode interface, which enhances the device performance. However, there is no agreement on the exact dipole direction in the literature. In this study, a peel‐off method to reveal the buried organic/metal interface to examine the energy‐level alignment is developed. By splitting the device at different interfaces, it is discovered that oppositely oriented dipoles are formed at different surfaces of the interfacial layer. Moreover, the function of the electrode interface differs in different device types. In organic light‐emitting diodes, the vacuum‐level alignment generally occurs at the organic/cathode interface, while in organic photovoltaic devices, the Fermi‐level pinning commonly happens. Both are determined by the integer charge‐transfer levels of the organic materials and the work‐function of the electrode. As a result, the performance enhancement by the cathode interfacial material in organic photovoltaic devices cannot be solely explained by the energy‐level alignment. The clarification of the energy‐level alignment not only helps understand the device operation but also sets up a guideline to design the devices with better performance.     

Ionic self-assembled monolayer for low contact resistance in inkjet-printed coplanar structure organic thin-film transistors

To reduce the contact resistance in inkjet-printed organic thin-film transistors (OTFTs), the use of a newly synthesized ionic self-assembled monolayer (SAM) consisting of an anchoring group, a linker group, and an ionic functional group, is investigated. According to the gated transmission line method (TLM) measurements of a series of OTFT devices, where one type has no charge injection layer, another type having a pentafluorobenzenethiol (PFBT) injection layer, and a third type containing a (6-mercaptohexyl)trimethylammonium bromide (MTAB) ionic SAM, the latter exhibits the lowest contact resistance value of ∼3.1 K Ω cm. The OTFTs without charge injection layer and with the PFBT SAM have relatively higher contact resistance values of ∼6.4 K Ω cm and ∼5.0 K Ω cm, respectively. The reduced contact resistance in the OTFTs with ionic SAMs is attributed to the large charge carrier density induced by the ionic SAM, which allows sufficient tunneling-assisted injection of the carriers from the metal electrode to the polymer semiconductor. These results suggest that the use of appropriate ionic SAM injection layer is an effective way to reduce the contact resistance, hence improving the charge transport characteristics of inkjet-printed OTFTs.     

Thermoelectric Properties of Polymeric Mixed Conductors

The thermoelectric (TE) phenomena are intensively explored by the scientific community due to the rather inefficient way energy resources are used with a large fraction of energy wasted in the form of heat. Among various materials, mixed ion‐electron conductors (MIEC) are recently being explored as potential thermoelectrics, primarily due to their low thermal conductivity. The combination of electronic and ionic charge carriers in those inorganic or organic materials leads to complex evolution of the thermovoltage (V_oc) with time, temperature, and/or humidity. One of the most promising organic thermoelectric materials, poly(3,4‐ethyelenedioxythiophene)‐polystyrene sulfonate (PEDOT‐PSS), is an MIEC. A previous study reveals that at high humidity, PEDOT‐PSS undergoes an ionic Seebeck effect due to mobile protons. Yet, this phenomenon is not well understood. In this work, the time dependence of the V_oc is studied and its behavior from the contribution of both charge carriers (holes and protons) is explained. The presence of a complex reorganization of the charge carriers promoting an internal electrochemical reaction within the polymer film is identified. Interestingly, it is demonstrated that the time dependence behavior of V_oc is a way to distinguish between three classes of polymeric materials: electronic conductor, ionic conductor, and mixed ionic–electronic conductor.     

动力学变质剂对激光选择烧结硬化层冷裂纹的抑制作用

从改变结晶状态的角度出发,研究了含硅、含锆等动力学变质剂对耐磨合金激光选择烧结成型的激励增塑作用,探讨了变质剂对烧结合金层化学成分及晶体形态的影响。结果表明,采用合适的动力学变质剂可以细化烧结合金层的组织,消除烧结合金层脆性开裂现象。     

Chameleon Nonwovens by Green Electrospinning

Electrospun ionic nonwovens are obtained by green electrospinning of aqueous dispersions. The resulting nonwovens are termed as chameleon nonwovens since their surface properties can be tailored in a large variety by coating of different functionalities following the protocol of the layer‐by‐layer process (LBL). The dimensional stability of the electrospun fibers in the chameleon nonwovens is achieved by photo‐cross‐linking after electrospinning and thereby overcoming the repulsive forces of the ionic moieties in the fibers. Depending on the nature of the ionic moieties different materials are coated by LBL including dyes, antibacterial materials, silver, and gold nanoparticles. Enhanced coating efficiency for coating of metal nanoparticles is observed when the chameleon nonwovens were precoated by a polyelectrolyte.     

Si(001)外延ZnSe薄膜界面原子的结合与成键

基于密度泛函理论的第一性原理计算,通过对Si(001)和氮化Si(001)表面单层Zn/Se原子结合的方式,模拟ZnSe外延薄膜的二维生长模式,从单层原子结合能、界面原子电子得失、共价结合成键的角度解释了Zn/Se原子在衬底表面的黏附性问题,阐述了薄膜生长初期界面无定形Se出现等现象,分析了氮化Si(001)表面对薄膜二维均匀生长的作用,结果显示N的引入缓和了Si衬底的非极性共价结合与ZnSe原子间的极性离子键结合之间的异质差异。     

Interface engineering in efficient vacuum deposited perovskite solar cells

We studied the effect of the charge transport layers in p-i-n perovskite solar cells using vacuum deposited methylammonium lead iodide thin-film absorbers. While solution-processed perovskite films are frequently deposited directly on PEDOT:PSS leading to good solar cell performances, in some cases even to very good V_oc values, we show that in devices employing vacuum deposited MAPbI₃ perovskites, the removal of the polyTPD electron blocker substantially reduces the photovoltaic behavior. This is indicative of rather different charge transport properties in the vacuum deposited MAPbI₃ perovskites compared to those prepared from solution. On the other hand, we investigated the use of ionic interlayers as a possible alternative to low work function electrodes, whose reactivity towards air and moisture compromises the device stability. Two different electron extraction materials were evaluated as interlayers between the fullerene electron transport layer and a silver electrode, in particular a perylenediimide derivative and a conjugated polyelectrolyte. By studying the photovoltaic response and the electroluminescence properties of planar diodes using the ionic films and comparing them with devices employing barium, we found that such ionic interlayers can successfully replace the use of reactive electrodes, since they facilitate the electron extraction while reducing the non-radiative recombination at the electron transport interface.     

Effect of multi-walled carbon nanotubes on electron injection and charge generation in AC field-induced polymer electroluminescence

We investigate the use of multi-walled carbon nanotubes (MWNTs) dispersed in an emissive layer of poly (N-vinylcarbazole) (PVK):fac-tris(2-phenylpyri-dine)iridium(III) [Ir(ppy)₃] in alternating current (AC) field-induced polymer electroluminescence (FIPEL) devices. A symmetric device structure, with the polymer/MWNT composite between two dielectric layers, was used to study the effect of MWNTs on charge generation within the active layer. An asymmetric device structure, using one dielectric layer, was used to study band alignment effects of carbon nanotubes in charge injection from a contact. The presence of MWNTs within the emissive layer facilitates effective internal charge generation in the symmetric devices, as would be expected if they acted as a charge source. However, electron injection under AC-driven fields also increases in the asymmetric devices, suggesting a modification to band alignment. Increase in light emission of five times is achieved in composite devices compared to devices with the pure polymer. From the trends in behavior with nanotube loading, we suggest that the nanotubes effectively doped the polymer, modifying energy level alignment in the device and increasing field-induced polarization currents. The combined effects of electron injection and charge generation may pave the way for widespread use of MWNTs in high-performance FIPEL devices.