Improving operation lifetime of OLED by using thermally activated delayed fluorescence as host

We fabricated organic light-emitting diodes (OLEDs) with the thermally activated delayed fluorescence (TADF) material of 4CzIPN, which show better stability compared with the 4,4’-Bis(carbazol-9-yl)biphenyl (CBP) based devices. The half lifetime of the device using 4CzIPN as host material has doubled, and a slower voltage rise compared with that of CBP-based devices has been achieved, which indicates the improvement of stability. We attribute the better stability to the good film morphology and difficult crystallization property of 4CzIPN. Our results suggest that employing the 4CzIPN as host material can be a promising way of fabricating OLEDs with longer operation lifetime.     

Co-doping method used to improve the charge transport balance in solution processed OLEDs

In this paper, co-doping method is used to improve the current efficiency of solution-processed organic light-emitting diodes (OLEDs). By changing the ratio of two thermally activated delayed fluorescent (TADF) emitters, we studied the performance of device and its mechanism. A solution processed OLED with a structure of indium tin oxide (ITO, 150 nm)/PEDOT:PSS (30 nm)/CBP:4CzIPN-x%:4CzPN-y% (30 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm) was fabricated. The current efficiencies of 26.6 cd/A and 26.4 cd/A were achieved by the devices with dopant ratio of 6% 4CzIPN:2% 4CzPN and 2% 4CzIPN:6% 4CzPN in emitting material layer (EML), respectively. By investigating the tendency of current density change in devices with different doping ratio, we suggested that the enhancement of the current efficiency should be due to the charge transport balance improvement induced by assist dopant in EML.     

Improved performance of CdSe/ZnS quantum dot light-emitting diodes through doping with small molecule CBP

The poor film formation of CdSe/ZnS quantum dots (QDs) during spin-coating makes a substantial impact on the device performance of quantum dot light-emitting diodes (QLEDs). This work proposes a method to improve the morphology of the quantum dot light-emitting layer (EML) by adding small organic molecular 4,4''-Bis(9H-carbazol-9-yl) biphenyl (CBP) into the layer. Its surface roughness reduces from 6.21 nm to 2.71 nm, which guarantees a good contact between hole transport layer (HTL) and EML. Consequently, the CdSe/ZnS QDs:CBP based QLED achieves maximum external quantum efficiency (EQE) of 5.86%, and maximum brightness of 10 363 cd/m2. It is demonstrated that the additive of small organic molecules could be an effective way to improve the brightness and the efficiency of QLEDs.     

紫外光改性银阳极对绿光OLED器件性能的影响

为提升OLED器件(结构为Ag/NPB/Alq3/LiF/Al)的性能,采用紫外光(UV)对银(Ag)阳极进行改性,探究阳极改性对器件性能的影响.研究结果表明:UV改性Ag阳极的时长为50 s时,器件性能最佳,启亮电压从20 V降低到6V,最大亮度从101.6 cd/m2提高到5 609.2 cd/m2,电流效率得到很大提升,且改性前后其发光峰的位置没有改变.UV改性使Ag阳极表面氧化生成氧化物,该氧化物薄层可作为空穴注入层,能够有效提高界面功函数,大大降低空穴注入势垒,提高了载流子注入能力,使绿光OLED器件的发光性能得到改善.这种利用UV改性Ag阳极的方法工艺简单,能有效降低空穴注入势垒,对提高该类柔性OLED器件的性能具有一定应用价值.     

透明叠层结构Ag/MoO_3/Ag阳极对绿光OLED器件性能的影响

本文采用一种结构为Ag/MoO_3/Ag的金属/氧化物/金属(M_1/O/M_2)叠层替代ITO作为OLED器件的阳极,研究Ag/MoO_3/Ag叠层结构变化对于OLED器件电极透过率、亮度、光谱等性能的影响。实验采用真空蒸镀方法制备了一系列器件,器件结构为Ag/MoO_3/Ag/MoO_3(10nm)/NPB(40nm)/Alq_3(60nm)/LiF(1nm)/Al(150nm)。对比器件的电压-电流密度、电压-亮度、光谱特性等数据,表明Ag/MoO_3/Ag的结构为20/20/10(nm)时,器件性能较好。在驱动电压为11V时,其亮度达到18 421cd/m~2,电流效率为2.45cd/A;且因器件中存在微腔效应,其EL光谱蓝移,半高宽变窄。但考虑到530nm处其电极透过率仅为17%,所以经换算该器件实际发光亮度比ITO电极器件更高。该Ag/MoO_3/Ag叠层阳极制作相对简单,经优化后在顶发射和柔性OLED器件方面将具有一定的应用前景。     

ZnO亚微米和微米棒的晶体生长及发光性质

用硝酸锌Zn(NO3 )2·4H2O和六亚甲基四胺 (CH2 )6N4,通过化学溶液法在玻璃衬底上生长出ZnO六角形亚微米和微米棒(长 5~6μm,直径 0. 8 ~5μm)。生长时间达两天后,ZnO棒呈中空六角形微米管。测量了样品的X射线衍射(XRD)谱,扫描电镜像和喇曼光谱。ZnO微米棒的光致发光为橙红色宽谱带发射(峰值 630nm, 半峰全宽 250nm), 其激发光谱除带间本征激发(短于 370nm)外,还有很强的在导带底附近的室温激子激发峰(峰值 387nm,半峰全宽 30nm)。而阴极射线发光有两个发射峰,橙色宽谱带强峰 (峰值580nm,半峰全宽约为140nm)是缺陷发光峰,近紫外窄谱带弱峰(峰值 395nm,半峰全宽约为 20nm)是激子发光峰。     

一步溶液法制备ZnO亚微米晶体棒及其发光性能

用硝酸锌(Zn(NO₃)₂·4H2O)或醋酸锌(Zn(CH₃COO)₂·2H2O)分别与六亚甲基四胺((CH₂)₆N₄)以等浓度0.005mol/L配制成两种反应溶液,通过化学溶液法在玻璃衬底上生长出ZnO六角型亚微米棒(长5~8μm,直径300~700nm)。测量了样品的XRD和扫描电镜像。经XRD分析,所得样品均为纤锌矿的ZnO六角型晶体。扫描电镜(SEM)像表明,生长时间为3h或5h时,样品为细长条的棒状结构,长径比超过10:1;生长48h后的ZnO亚微米棒的一端被腐蚀成一定深度的ZnO亚微米管。用负离子配位四面体生长模型分析了ZnO亚微米棒的生长机理。ZnO亚微米棒退火前后的光致发光谱表明,退火处理后的发射谱中的紫外峰消失,而红色发光峰红移并且增强(峰值由630nm左右移到710nm),同时它的激发光谱中的室温激子激发峰也增强。     

水浴法制备形貌可控的一维ZnO纳米和微米棒

用一步或两步简单的化学溶液法,以醋酸锌为原料,六亚甲基四胺或三乙醇胺为催化剂在玻璃衬底上生长出不同形貌的纳米和微米ZnO棒.探讨了反应液的酸碱度和反应液浓度对生成的ZnO棒形貌的影响,并分析了其生长机制.随着溶液浓度的增加,棒的长度与直径比减小,同时玻璃衬底上生长的ZnO棒从无序分布趋于垂直于衬底平行取向分布.随着pH值的改变,棒的形状由在弱酸性溶液中的细长棒状变为在弱碱性溶液中的圆头对称短棒;当碱性增大到一定程度时,可以生成颗粒状.通过控制一定的酸碱度和溶液浓度,可以得到规则的六角ZnO棒状阵列.测量了样品的XRD和扫描电镜像,并对其发光性能进行了测量分析.其中规则有序六角棒的发光光谱表明峰值在530nm,半高宽为220nm,可能是Vo+的电子和价带中的空穴辐射复合所致.     

反射式胆甾相液晶显示器件双稳特性的研究

主要利用反射光谱特征曲线来研究摩擦取向对反射式胆甾相液晶显示器件双稳特性的影响,研究表明未经摩擦PI层不具有取向作用,由于其较高的预倾角和表面非均匀性,有利于胆甾相液晶形成多畴结构,实现双稳态显示,同时该器件具有较高的对比度,能实现不同灰度。     

眼科准分子激光实时监控能量计

利用激光感生热电电压(LITV)效应制成了激光功率/能量计,它不仅能测量和记录每个脉冲的能量值及实时施加的脉冲总能量等信息,也能记录每个入射脉冲的响应波形,实现了对激光能量的实时监控。用此功率/能量计对248 nm准分子激光器进行模拟实验。测量结果表明,在1~50 Hz重复频率下,激光器输出能量的相对标准偏差在8.6%~10.7%。在模拟屈光手术设置参数下,对193 nm准分子激光器进行测量,表明此激光器输出能量的相对标准偏差在8.3%。将这种激光功率/能量计用于激光近视眼科手术中,对提高激光的切削质量和手术质量有重要意义。