非常榮幸能夠擔任光電所學會會長。首先要感謝光電所的各位同學，願意給我一個機會為大家服務。在這裡也要感謝江宏禮同學，以及潘昆懋同學，幫我處理了許多所學會以及實驗室的事務，讓我可以無後顧之憂。

從2007年的9月入學迄今，在光電所這個大家庭也度過了一年的光景。我想會讓我擔任所學會會長的原因有很多，最重要原因的在於，在光電所這一年生活當中，我和大家一起上課、做實驗、踢球、聯誼。幾乎大部分的時間都是與同學們度過。我開心時，同學們總是願意 傾聽分享我的喜悅；而在我失落遇到挫折時，身邊的朋友們也帶給我許多建議與鼓勵。這段時間內，我感受到光電所的老師與同學們帶給我的溫情，讓我了解自己是這個大家庭裡的一份子，更希望自己也能為光電所盡一份心力，把自己體會到的喜悅帶給大家。

有鑑於過去的一年中，常聽到同學在討論，相對於電資學院其他研究所而言光電所的活動實在太少，不免有些遺憾。因此在未來的一年中，所學會的重心將放在為同學們舉辦聯歡活動，類型豐富，以期能夠促進各實驗室的感情。活動包括有餐會、運動比賽，以及藝文活動等，敬請期待，並請大家踴躍參與。同時我們期望能夠建立起學生跟所辦公室以及教授之間溝通的管道，讓學生們能夠對光電所的事務發表建議。

雖然跟光電所許多的前輩比起來，我無啻是個新人。但我願以一顆充滿熱誠的心，在任期內全心奉獻於所學會。也請光電所的每一份子不吝批評指教與協助，讓所學會能夠為大家提供最完美的服務。

FIG. 1a. Transmission change of as-grown SiO_1.25 and CO₂ laser annealed SiO_1.25 at Plaser=6 kW/cm². (Inset: Transmission spectra of pure quartz)

FIG. 1b. Absorption spectra of as-grown SiO_1.25 and CO₂ laser annealed SiO_1.25 at Plaser=6 kW/cm². (Inset: The calculated absorption spectra of Si₂₉H₂₄ and Si₂₉H₃₆)

FIG. 2. Optical band gap of CO₂ laser annealed SiO_1.25 as a function of laser intensity. (Inset: Tauc plot, (ahn) ^1/2 as a function of photon energy (hn) for as-grown SiO_1.25 sample and CO₂ laser RTA SiO_1.25 samples at Plaser from 6 to 12 kW/cm²)

FIG. 3a. PL spectrum of PECVD-grown SiO_1.25 annealed at CO₂ Plaser of 7.5 kW/cm² and transmission change of as-grown SiO_1.25 and CO₂ laser annealed SiO_1.25 at Plaser of 6 and 7.5 kW/cm².

Patterned microlens array for efficiency improvement of small-pixelated organic light-emitting devices

Research groups of Prof. Hoang-Yan Lin and Prof. Jiun-Haw Lee

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

(e-mail) hylin@cc.ee.ntu.edu.tw

臺灣大學光電所林晃巖教授

　We experimentally and theoretically investigated the optical characteristics of organic light-emitting devices (OLEDs), having different pixel sizes and attached with patterned microlens array films. For a regular microlens array (Fig. 1(b)), though it can extract the waveguiding light and increase luminous current efficiency for a large-pixelated OLED, we observed that it decreased the luminance to an even lower level than that of the planar OLED as its pixel size was close to the microlens dimension (Fig. 2). Although a microlens can effectively outcouple the light rays originally at incident angles larger than the critical angle, it also can impede the outcoupling for the light rays originally at incident angles smaller than the critical angle. Enhancement or reduction of the light extraction depends on the relative positions of the light emitting point and the microlens. Therefore, we proposed a center-hollowed microlens array (Fig. 1(c)), of which the microlenses directly upon the pixel are removed, and proved that it can increase the luminous current efficiency and luminous power efficiency of a small-pixelated OLED. As can be seen from Fig. 3, by attaching this patterned microlens array, 87% of luminance enhancement in the normal direction was observed for a 0.1´0.1 mm² OLED pixel. On the other hand, a regular microlens array resulted in 4% decrease under the same condition.

Electrical and Optical Characteristics of OLED with Bipolar Emitting Layer

Research group of Prof. Jiun-Haw Lee

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所李君浩教授

　One of the root causes which limits the operation lifetime of organic light-emitting device (OLED) is the charged carriers piled-up at the interface of transporting layer and emitting layer (EML). By introducing the bipolar EML, the recombination zone in an OLED becomes wider which effectively elongated the operation lifetime. We have demonstrated the performance improvement and studied the electrical and optical characteristics of OLEDs with bipolar EML quantitatively and qualitatively.

　We used high-electron-mobility ETL material, bis(10-hydroxybenzo[h] qinolinato)beryllium (Bebq₂), mixed with a-naphthylphenylbiphenyldiamine (NPB) as the bipolar EML. We have demonstrated an OLED with a luminance of 27600 cd/m² at only 5 V, and a lifetime four times longer than that of a conventional device. Since the recombination zone was wider, the maximum luminance in a bipolar OLED can be as high as 288000 cd/m² with the current density over 7 A/cm², which may be suitable for flashlight applications. Not only the performance improvement, we also discussed the carrier transport characteristics in a bipolar EML from current-voltage characteristics and the recombination process from the electro-luminescence measurement. We found an optimized mixing ratio which was NPB:Bebq2=1:1 with highest current density due to the electron-hole balance in this bipolar EML. The spectral shift was due to the recombination shift and the solid-state solvation effect.

　Besides, we used two different methods to quantitatively investigate the recombination zone in the MH-EML consisting of NPB and tris-(8-hydroxyquinoline) aluminum (Alq3). The first method was by using rigorous electrical and optical models to simulate the carrier distribution, recombination distribution, and EL spectra in the MH-OLED. By fitting the J-V curves and the spectra with different mixing ratios, the mobility values can be extracted. Electron (hole) mobility decreased (increased) monotonically with increasing the NPB ratio. However, the driving voltage increased then decreased due to the competition between the hole-current enhancement and the electron-current decline. For the second method, we used a thin 4-(dicyanomethylene)-2-tert-butyl-6-1,1,7,7-(tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) layer with the thickness of 1.2 nm and the volume concentration of 2% as a probe to determine the recombination zone. Besides, we also found that when the probe position overlapped the maximum recombination position, a voltage reduction of 1.97 V was observed. It can be well explained by the enhancement of the recombination current from the continuity equation. This result suggested that the driving voltage of an OLED with the bipolar EML can be reduced by inserting a dopant in a suitable region. A white OLED was fabricated with selectively doping a yellow dopant in the blue EML which exhibits high efficiency and low driving voltage.

摘要

在藍光磷光元件的開發上，高三重態能階主體材料是一項重要關鍵。故我們首先研究具有高三重態能階之電洞傳導材料與電子傳導材料，以及高效率之藍光磷光元件結構。次一主題是探討新型多功能主體材料；其後並具體實現單層之高效率紅光磷光元件。接著藉由高三重態能階雙極性傳導材料之開發，成功地將高效率單層磷光元件推展到綠光與藍光。此外，我們對於使用磷光主體材料以利用偶極矩作用能量轉移機制之元件亦有探討。本論文最後則研究混合螢光與磷光之白光有機發光元件，以期能實現固態照明之應用。