Professor Chih-I Wu's Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 吴志毅教授

For typical organic light emitting devices (OLEDs) with the hole mobility much larger than the electron mobility, the impedance versus voltage (Z-V) characteristics show a particular behavior which can be used to investigate many electrical properties of the organic layers. The impedance of these devices presents a transition from a higher value to a lower value before the device turns on, which indicates that the hole transport layer (HTL) reaches flat band and becomes conductive first. The voltage at where this transition occurs is named the transition voltage, and the difference between the transition voltage and the turn on voltage is dependent on the thickness of the electron transport layer (ETL) and the density of the accumulation charges.

In this work, devices with systematically varied thicknesses of ETLs and four kinds of cathode structures were investigated. The transition voltages versus the thickness of the ETL characteristics in Fig. 1 show that the transition voltages of the devices with an electron injection layer (EIL) shift toward higher bias while the slopes of all these devices remain constant. The shift of the transition voltage is proposed to result from the diffusion of the cathode structures into the organic layers which decreases the effective thickness of the ETL for capacitances. Therefore, the diffusion length of these cathodes can be estimated from the shift of the transition voltages of each group of devices.

Fig.1 The transition voltage V0 versus thickness of the ETL (Alq3) characteristics. The film structures of these devices are ITO/NPB(800Å)/Alq3/cathodes.

 Professor Jian-Jang Huang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 黄建璋教授

Traditional methods of detecting cancer cells, such as fluorescence, have their limits and can hardly be used for identification during tumor resection. Here we report an alternative tumor detection technology using ZnO nanorods bonded to antibodies as cancer cell probes. Our experiment shows that EGFR(Epidermal growth factor receptor) can be connected to ZnO nanorods and to EGF receptors of SCC(squamous cell carcinoma). The cancer cell can be recognized by the bare eye or the optical microscope with the help of purple light emission from ZnO/EGFR antibody probes. On the other hand, for cells with less expression to EGFR, in our case HS68, no purple light was observed as the probes were washed-off. From the photoluminescent spectra, the peak intensity ratio between the purple light (from ZnO at the wavelength 377nm) and the green band (from the auto-fluorescence of cells) is much higher with the presence of SCC, as compared with HS68. The ZnO/EGFR antibody probes have the potential to be applied to real time surgery for tumor cell identification. The cancer cells will be excised with the help of purple light emission.

(a)	(b)
(c)	(d)
(e)	(f)
Fig.1 Experimental flow of ZnO antibody probes bonded to SCC(cancer cells) (a) and HS68 (b). The nanorods without antibody were also employed for comparisons. (c)&(e) The strong UV-VIS band ratio indicates the existence of SCC while very weak UV light for HS68 samples ((d)&(f)).

 Professor Hoang-Yan Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所 林晃岩教授

Solar-cell-integrated organic light-emitting diodes (OLEDs) were fabricated with both high contrast ratio and energy-recycling ability. However, the luminous efficiency of the integrated devices is reduced to 50% of that of conventional top-emitting OLEDs. A novel structure to recover the luminous efficiency from 50% to near 85% by applying a distributed Bragg reflector (DBR) was demonstrated. It saves about 40% of the electric power of that of a device without a DBR. The contrast ratio remains high compared to that of conventional OLEDs. Simulations were conducted first to prove our models and assumptions. Then, two types of thin-film solar cells – CdTe and CIGS solar cells – were used. They had different contrast ratios as well as viewing-angle properties. Finally, the emission spectrum was calculated to be 11 nm FWHM, which is narrower than that for the emission spectrum of a typical microcavity OLED and has the advantage of having saturated colors.

Fig. 1 (a) Concept of the solar-cell-integrated OLED; (b) concept of our DBR design; integration of a DBR to enhance the outcoupling efficiency.

Fig. 2 (a) Input microcavity-OLED emission spectrum; (b) DBR reflectance of a CdTe solar-cell-integrated OLED; (c) output microcavity-OLED emission spectrum for a CdTe solar-cell-integrated OLED.

姓名：裴善庄   指导教授：黄升龙教授

论文题目：玻璃包覆之晶体光纤宽带光源

姓名：许光裕   指导教授：黄升龙教授

— 数据提供：影像显示科技知识平台 (DTKP, Display Technology Knowledge Platform) —

— 整理：林晃岩教授、陈圣灏 —

在光子晶体中抑制自发性辐射

荷兰特温特(Twente)大学的科学家日前以实验结果展示了一个近四分之一个世纪前的预测：可藉由三维光子晶体(photonic crystal)产生之能隙结构来抑制自发性辐射(spontaneous emission)(相关论文：Phys. Rev. Lett. 107, 193903)。藉由了解此辐射以及其抑制方法，研究人员在未来可以建立出更好的固态激光以及减少量子计算机(quantum computers)中可能出现之噪声。

Willem Vos和Merel Leistikow与其同事，经由在硅芯片上蚀刻出正交排列的孔洞数组，建立出一个"反式木垛"(inverse woodpile, 木垛：摆放成堆之木头)之光子能隙结构，经由理论计算方法得出此结构所产生之能隙，可使得所有的模态皆无法存在。

图 1 (a) 电子显微镜下之三维反式木垛结构，由互相垂直之孔洞数组排列组成(被二维光子晶体结构所包围，见红色虚线处) (b) 反式木垛结构参数示意。

在制作出所需光子晶体结构之后，研究人员将其浸泡至由硫化铅(lead sulfide)制作出之量子点胶体溶液中(室温条件下此溶液会发出波长约在1.39 ~1.50 μm的通讯波段)，并利用532 nm波长的短脉冲激光激发量子点，根据Willem Vos的说明，激发后的量子点可视为单一光子源，由于由量子点所发出之辐射非常低，研究人员须仔细地将背景噪声去除，并花费数小时来收集其辐射。

如同预测之结果，量子点在光子能隙作用下，其辐射衰减率(decay rates)缩减为原本的十分之一，然而在光子能隙外则有两倍的增强，换句话说，处在光子晶体结构中之量子点比未经任何处理之量子点需要十倍的时间才会辐射。在一个实际有限尺寸之光子晶体，此抑制之效应取决于量子点与结构表面之距离。