Professor Chih-I Wu's Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 吳志毅教授

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.

 Professor Jian-Jang Huang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 黃建璋教授

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

臺灣大學光電所 林晃巖教授

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：裴善莊   指導教授：黃升龍教授

論文題目：玻璃包覆之晶體光纖寬頻光源

姓名：許光裕   指導教授：黃升龍教授

— 資料提供：影像顯示科技知識平台 (DTKP, Display Technology Knowledge Platform) —

— 整理：林晃巖教授、陳聖灝 —

在光子晶體中抑制自發性輻射

荷蘭特溫特(Twente)大學的科學家日前以實驗結果展示了一個近四分之一個世紀前的預測：可藉由三維光子晶體(photonic crystal)產生之能隙結構來抑制自發性輻射(spontaneous emission)(相關論文：Phys. Rev. Lett. 107, 193903)。藉由了解此輻射以及其抑制方法，研究人員在未來可以建立出更好的固態雷射以及減少量子電腦(quantum computers)中可能出現之雜訊。

Willem Vos和Merel Leistikow與其同事，經由在矽晶片上蝕刻出正交排列的孔洞陣列，建立出一個"反式木垛"(inverse woodpile, 木垛：擺放成堆之木頭)之光子能隙結構，經由理論計算方法得出此結構所產生之能隙，可使得所有的模態皆無法存在。

圖 1 (a) 電子顯微鏡下之三維反式木垛結構，由互相垂直之孔洞陣列排列組成(被二維光子晶體結構所包圍，見紅色虛線處) (b) 反式木垛結構參數示意。

在製作出所需光子晶體結構之後，研究人員將其浸泡至由硫化鉛(lead sulfide)製作出之量子點膠體溶液中(室溫條件下此溶液會發出波長約在1.39 ~1.50 μm的通訊波段)，並利用532 nm波長的短脈衝雷射激發量子點，根據Willem Vos的說明，激發後的量子點可視為單一光子源，由於由量子點所發出之輻射非常低，研究人員須仔細地將背景雜訊去除，並花費數小時來收集其輻射。

如同預測之結果，量子點在光子能隙作用下，其輻射衰減率(decay rates)縮減為原本的十分之一，然而在光子能隙外則有兩倍的增強，換句話說，處在光子晶體結構中之量子點比未經任何處理之量子點需要十倍的時間才會輻射。在一個實際有限尺寸之光子晶體，此抑制之效應取決於量子點與結構表面之距離。