Guided Wave Studies of Reflective MTN Liquid Crystal Cell

The fully-leaky guided wave technique has been used to study the reflective 90? MTN liquid crystal cell used for LCOS. The cell is comprised of upper substrate with indium-tin-oxide coating and lower substrate with aluminum coating. Reflective angle-dependent signals (Rss, Rpp, Rsp and Rps) were recorded over a range of angles of incidence with the cell under application of 0 - 7 Vrms ac electric fields. From the recorded experimental data, we found the reflective signals are quite strong, especially the polarization conversion signals. Fitting the data in reflection with the results of the modeling-program gives the information about the pre-tilt and twist of the director as well as the parameters of different optical layers. We found that the pre-tilt angle on the upper substrate is different from that on the bottom in the best fits, which suggests that the indium-tin-oxide and the aluminum coatings have different effects on the alignment layers.

Charge distribution into illuminated dye-doped surface stabilized ferroelectric liquid crystal cell

Surface stabilized （anti） ferroelectric liquid crystal cells can be used as an optically addressed media for optical data processing. The structure of the cell has to contain a photo sensible agent, i.e, an absorbing dye-doped orienting layer. The all-optical generation of the diffractive grating can be done due to the switching parameters of the smectic slab within cells with a sensitive layer. This Letter considers a study of the optically induced charge generation into the dye-doped layer, and the explanation of the phenomena of the selective molecular director reorientation, while cell driving what leads to the induction of phase grating.

Viewing angle characteristics of a nematic liquid crystal cell with two crossed-grating surface substrates

Liquid crystal in a nematic liquid crystal cell surface with two crossed-grating surface substrates can be oriented along the normal grating direction with given geometric parameters of groove and anchoring strength. This display is equivalent to multi-domain vertical-alignment mode. It has a relatively wide viewing angle. In this letter, we investigate the viewing angle characteristics of this kind of cell. The viewing angle dependence of contrast ratio is obtained using the extended Jones matrix method, which also considers the flexoelectric effect. The viewing angle is dependent on the geometric parameter of grating surface, the flexoelectric coefficients, and the anchoring strength. Therefore, appropriate value for each factor needs to be selected to obtain a better viewing angle of this cell.

Fullerene solar cells with cholesteric liquid crystal doping

This paper reports the doping effect of cholesteric liquid crystal 3β-Hydroxy-5-cholestene 3-oleate on polymer solar cells composed of the poly 3-hexyl thiophene and the fullerene derivative.With a doping ratio of 0.3 wt%,the device achieves an ideal improvement on the shunt resistor and the fill factor.Compared with the reference cell,the power conversion efficiency of the doped cell is improved 24%.The photoelectric measurement and the active layer characterization indicate that the self-assembly liquid crystal can improve the film crystallization and reduce the membrane defect.

Fabrication and Characterization of Bulk Heterojunction Solar Cells Based on Liquid-Crystal Semiconductive Polymer

Bulk heterojunction solar cells based on poly poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) as liquid crystal semiconductive polymer and C60 as electron acceptor were fabricated and characterized. Thermal treatment of the bulk heterojunction films at annealing in the range of glass temperature and liquid crystal transition was performed for tuning optimization with improving the photovoltaic and optical properties. The photovoltaic performance was depended on morphological behavior in active layer at crystal state below glass temperature. The F8T2 thin film worked for electron-donor layer as p-type semiconductor to support charge transfer in active layer. Mechanisms of the photovoltaic properties were discussed on the basis of experimental results.

Al_xGa_(1-x)As/GaAs Solar Cell Grown by Multi-substrate Liquid Phase Epitaxy

A novel horizontal push-pull multi-substrate epitaxy boat with three separate cells is introduced in this article, with which multi-substrate LPE processing is feasible in horizontal LPE furnace. The processes of LPE AlxGa1-x)As/ GaAs solar cells are studied and the efficiency of the solar cells achieved 19.8% （AMO, 25℃, 120 mW/cm2）.

液晶器件制备虚拟仿真实验平台的设计与教学实践

针对液晶器件制备实验设备多、成本高、安全隐患大、实验时间长等问题,采用client/server和browser/server混合架构建设了液晶器件制备虚拟仿真实验平台,该实验平台高度仿真了液晶器件制备的完整过程.平台同时建立了实验预习、虚拟操作练习和项目考核的多维度、全过程考核评价方法.从实践教学效果来看,平台的建设能够使学生系统掌握液晶器件制备流程,提高了学生自主学习能力、操作能力和创新能力.

快速响应模式电极pi-cell液晶透镜的研究

为提高传统模式电极液晶透镜的响应速度,本文设计了模式电极pi-cell液晶透镜。结合液晶连续体理论和模式电极液晶透镜电阻-电容等效电路,提出一种快速的计算方法对液晶透镜进行模拟仿真,仿真结果与实际器件的测试参数具有良好的一致性,显示了此仿真方法具有较高的精度,并依据仿真结果设计了模式电极pi-cell液晶透镜的驱动条件。实验制备了模式电极pi-cell液晶透镜并研究了其光学特性,结果显示此液晶透镜具有较大的焦距调节范围和良好的成像效果,对比于参数相近的模式电极平行排列液晶透镜,模式电极pi-cell液晶透镜的响应时间为136ms,比平行排列液晶透镜减少368ms,响应速度显著提高。

柱筒中掺杂手性剂向列相液晶的介电及挠曲电性能

在电场作用下,同心圆柱筒中的介电作用及挠曲电作用具有与平面液晶盒中不同的性质。本文在轴向强锚定边界条件下,对柱筒内添加手性剂的向列相液晶5CB施加径向电场,分别研究了介电效应和挠曲电效应对指向矢分布的影响。基于液晶连续体弹性理论和有限差分迭代方法,计算了体平衡态方程。通过数值计算发现,挠曲电系数e1、e3具有不同的取向作用。本文的模拟结果为电场作用下柱筒内手性向列相液晶指向矢结构的预测提供了更全面的理论分析,对液晶挠曲电系数的测量也具有一定的指导意义。

Ionic liquid crystal-based electrolyte with enhanced charge transport for dye-sensitized solar cells

A room temperature ionic liquid crystal,1-dodecyl-3-ethylimidazolium iodide(C12EImI),and an ionic liquid,1-decyl-3-ethylimidazolium iodide(C10EImI),have been synthesized,characterized and employed as the electrolyte for dye-sensitized solar cells(DSSC).The physicochemical properties show that a smectic A(SmA)phase with a lamellar structure is formed in C12EImI.Both C12EImI and C10EImI have good electrochemical and thermal stability facilitating their use in DSSC.The steady-state voltammograms reveal that the diffusion coefficient of I3–in C12EImI is larger than that in C10EImI,which is attributed to the existence of the SmA phase in C12EImI.Because the iodide species are located between the layers of imidazolium cations in C12EImI,exchange reaction-based diffusion is increased with a consequent increase in,the overall diffusion.The electrochemical impedance spectrum reveals that charge recombination at the dyed TiO2/electrolyte interface of a C12EImI-based DSSC is reduced due to the increase in I3–diffusion,resulting in higher open-circuit voltage.Moreover,both short-circuit current density and fill factor of the C12EImI based DSSC increase,as a result of the increasing transport of I3–in C12EImI.Consequently,the photoelectric conversion efficiency of C12EImI-based DSSC is higher than that of the C10EImI–based DSSC.

单分子液晶添加剂在甲脒铅碘钙钛矿太阳能电池中的应用

溶液制备的钙钛矿薄膜通常含有大量晶界,会降低薄膜结晶质量,导致缺陷复合,不利于提升器件性能。因此,制备更高结晶质量的薄膜来进一步提升能量转化效率是钙钛矿太阳能电池面临的挑战。液晶分子具有强的自组装能力和形貌调节能力,本研究引入一种向列型单分子液晶4-氰基-4′-戊基联苯(5CB)作为甲脒铅碘(CH(NH2)2PbI3,FAPbI3)钙钛矿前驱液的添加剂,可以增大钙钛矿晶粒尺寸,减少晶界。此外,5CB的氰基能钝化钙钛矿晶粒表面未配位的Pb^(2+),降低缺陷态密度,从而抑制非辐射复合。经过优化,添加0.2 mg/mL 5CB的钙钛矿太阳能电池的能量转化效率达到21.27%,开路电压为1.086 V,电流密度为24.17 mA/cm^(2),填充因子为80.96%。本研究证明使用单分子液晶作为添加剂是提升FAPbI3钙钛矿电池性能的有效策略。

基板锚定特性对液晶盒电容的影响

基板的锚定特性,包括锚定能大小和锚定易取方向,影响液晶指向矢的分布,直接导致液晶盒电容的改变,因此可以通过液晶盒电容的测量确定基板表面的锚定特性。基于液晶弹性理论和变分原理,理论推导弱锚定平行排列向列相和混合排列向列相液晶盒系统的平衡态方程和边界条件,采用差分迭代方法数值模拟得到了液晶盒约化电容随电压、锚定能系数及锚定易取方向变化的曲线。结果表明:液晶盒电容随基板锚定能系数的增加而减小;随预倾角的增加,液晶盒电容随锚定能系数的变化缩小;同一电压和基板锚定能系数下,平行排列向列相液晶盒电容不会大于混合排列向列相液晶的电容。

平行排列向列相液晶的导波研究

基于透镜扩束系统,应用棱镜耦合技术对液晶层的全漏导模特性进行了研究。采用盒厚为4.6μm的平行排列向列相液晶盒,其内灌注E7液晶,通过实验给出了平行排列向列相液晶薄层的导波图,进而将实验结果与理论模拟结果进行了比较,理论所预言的液晶波导的导模在实验的导波图上得到了很好的验证。

液体结构与热导率模型

为了深入探讨液体结构对热导率的影响,假设液体由微型晶粒和空穴组成,在有效结构理论基础上用晶体学和气体分子运动论的方法推导出一个双参数热导率模型:g3/2Cs7/2s2s7/4/)(ΩVMTVVVCVVVVTDλ-+-=,该模型能够较好地适用于不同液体物质热导率的关联。由关联数据定性讨论了特征参数D和C的物理意义,解释了特征参数D和物质晶胞参数间的良好定量关系。结果表明模型参数的数值和符号较好地表达了液体的结构特点和导热机理,进一步说明了该热导率模型的合理性。

液晶盒电容的测量

分别采用交流谐振和交流电桥的方法对混合排列向列相液晶盒电容进行了测量,得到了液晶空盒的谐振曲线和液晶盒的电容-电压特性曲线,由此给出了对应两种情况的液晶盒电容值,并与理论值进行了比较,理论值和实验值拟合得很好,说明交流电桥方法是测量液晶盒电容的一种有效的方法。

聚合物稳定液晶调光器件厚度对其电光性能的影响

通过采用紫外光聚合诱导相分离法制备聚合物稳定液晶调光器件,利用紫外可见分光光度计来研究器件的不同厚度对聚合物稳定液晶调光器件电光性能的影响.结果表明:随着器件厚度的增加,器件的关态透光率降低,阈值电压升高,饱和电压升高;当器件厚度为5μm时,聚合物稳定液晶智能调光器件的电光性能优良,未通电时,透光率高达97%,当施加40 V电压时,透光率低于10%;响应时间非常短,灵敏度非常高,从关态到开态响应时间仅仅需要0.025 s,从开态到关态响应时间需要0.060 s.这些优异性能使得基于聚合物稳定液晶的智能窗在室内光线智能管理领域有着巨大的应用潜力.

改进的极向锚定强度测量方法

介绍一种测量液晶表面极向锚定强度的方法,通过同步测量线性偏振光经过混合排列的楔形液晶盒的相位及外加电压值,经过数值处理,得到表面极向锚定强度。使用混合排列液晶盒,简化了计算及测量步骤;使用楔形盒并用不同点的厚度差值代替厚度值计算,减小了由于厚度测量误差引起的干扰,提高了测量精度。

彩色液晶显示器件色差补偿优化

为了改善彩色液晶显示器件的色差,提升画面品质,针对(128,192,192)灰阶图形下色差的问题,对色差产生的机理进行了分析。模拟了RGB三色像素透过率对该图形下色差的影响。通过分别调整RGB彩膜膜厚,不仅相对调整了三色像素下的液晶盒层厚,而且还调整了三色像素的透过率,改善了RGB的Gamma曲线,对色差进行了补偿优化。实验结果表明,增加G像素和减小B像素的液晶盒层厚,对色差有明显补偿改善效果;同时,当RGB膜厚保持不变时,色差与液晶层厚呈正比关系,液晶层厚每减小1%时,色差约降低0.2。当RGB三色液晶盒层厚从(3.47,3.38,3.4)μm分别调整到(3.5,3.45,3.36)μm和(3.5,3.44,3.28)μm时,(128,192,192)灰阶图形下样品色差平均值从13.8分别降低到12.8和12。通过分别调整RGB彩膜膜厚,相对调整了三色像素下的液晶层盒厚和液晶量调节,可以一定程度优化补偿色差。

表面弹性自由能k_(13)项与楔形液晶盒中阈值厚度附近的指向矢分布

考虑楔形液晶盒,液晶指向矢倾角θ是两个空间变量x,z的函数,即θ=θ(x,z)。导出了液晶盒的吉布斯自由能,其中包括表面弹性自由能k13 项。由拉格朗日 欧拉方程得到了θ(x,z)满足的微分方程。在k11 k33近似下,方程变为二维拉普拉斯方程。在阈值厚度 hc 附近θ很小,方程的解可近似为θ=cz(qx-1)。代入自由能表达式中,求极值可确定 c和q 的值。计算和讨论了k13项对液晶指向矢分布的影响。

偏光干涉法检测LCD间隔子的均匀性

由于液晶显示器中间隔子的均匀性影响着对比度、色调变化等性能,因此,本文对液晶显示屏间隔子均匀性的检测方法进行了研究。首先分别利用干喷和湿喷法制备了对应的液晶盒,然后采用偏光显微镜研究了所制备液晶显示屏间隔子的分布特性。研究发现,正常情况下,液晶盒内间隔子最小距离接近20μm,最大距离超过100μm;间隔子分布不良的主要缺陷为间隔子团聚;在实验室条件下,干喷法间隔子团聚比较严重,湿喷法基本上无此现象。所以,利用偏光干涉法,通过调节偏光显微镜上下偏光片的相对角度,可以在不破坏液晶显示屏的前提下直接观察到其内部的间隔子及间隔子的分布情况。文中还分析了利用偏光干涉检验间隔子均匀性的原理。