高效率真空蒸鍍有機光電元件之元件與光學工程

Device and Optical Engineering for Efficient Vacuum-Deposited Organic Optoelectronic Devices

康皓維

指導教授 ： 林皓武

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

摘要

本篇論文研究以真空蒸鍍製程之有機光電元件的光學與元件結構對元件表現的影響。
首先，介紹有機太陽能電池的歷史及目前發展現況，接著講解有機太陽能電池的運作機制、元件結構種類、有機材料基本性質分析、元件製作與量測分析。
論文的第二部份，將探討陰極緩衝層材料與結構對於有機太陽能電池元件表現的影響，我們以NTCDA與PTCBI搭配製作出能任意調整厚度的光學間隔層，並在PTCBI上覆蓋一層金屬Ca以增加元件穩定性；另外，我們以Bphen搭配Ca的雙層陰極緩衝層作為電子萃取層，使用雙層陰極緩衝層的元件能夠較只有Bphen陰極緩衝層的元件有更佳的效率。
論文的第三部分，介紹一系列小分子donor的發展進行文獻回顧。在D-A型式分子中，D-π-A-A的DT4MIDTP與C70以體積比1:1的共蒸鍍比例所製作的平面混合異質接面結構元件有最佳的元件表現，元件效率高達4.22 %，並在製作成平面混合異質接面串聯結構元件後，將元件效率進一步提升至4.6 %。之後我們探討DT4TIDTP與DT4MIDTP兩D-π-A-A型式分子在經過熱退火處理後分子的光電特性改變。在平面型異質接面元件中，DT4MIDTP元件在適當溫度的pre-annealing處理後元件效率從1.3 %提升至2.5 %，並在製作成平面型異質接面串聯結構元件後，將元件效率進一步提升至2.87 %。而在oligothiophene分子中，DTPTtDCV與C70以體積比1:1.5的共蒸鍍比例所製作的平面混合型異質接面結構元件有最佳的元件表現，元件效率達3.02 %。
論文的第四部份，我們將金屬微共振腔結構應用於光響應元件中，以光學模擬搭配實驗製作出高效率全可見光頻譜光響應元件，並在適當的抗反射層厚度與微共振腔長度下，金屬微共振腔光響應元件能夠在特定波長範圍內比ITO陽極元件有較高的光響應。接著我們以有機材料製作出具週期性結構的wrinkle表面，在嘗試不同材料搭配與製程條件後，成功製作出週期接近於可見光的奈米結構。最後我們將wrinkle表面應用於有機太陽能電池與有機發光二極體中，利用奈米結構增加元件的in-coupling/out-coupling的特性，成功提升元件效率。

關鍵字

有機光電元件 ； 有機小分子 ； 真空蒸鍍 ； 元件光學工程

並列摘要

In this thesis, I focus on the optical properties and device engineering of vacuum-deposited organic optoelectronics.
In the first part, I briefly review the development of organic solar cells (OSCs), followed by working mechanisms, device structures of OSCs, material analyses, device deposition methods and measurements of OSCs.
In the second part of thesis, 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) and 3,4,9,10-perylenetetracarboxylic-bisbenzimidazole (PTCBI) were used to replace 2,9-dimethyl-4,7-di(phenyl)-1,10-phenanthroline (BCP) as optical spacing layer in OSCs. Furthermore, a Ca buffer layer is capped on PTCBI to modify morphological roughness. In addition, an effective bilayer cathode buffer layer for highly efficient small molecule organic solar cells (SMOSCs) is demonstrated. By integrating 4,7-di(phenyl)-1,10-phenanthroline (Bphen)/1 nm Ca bilayer buffer layer, the power conversion efficiency (PCE) enhances over 20 % compared to a device with a traditional Bphen buffer layer.
In the third part, before evaluating new donor compounds for SMOSCs, I review some previous studies of small molecular donors employed in SMOSCs . Among all donor-acceptor (D-A) structured donor compounds in this study, DT4MIDTP, a donor with the donor-π bridge-acceptor-acceptor (D-π-A-A) molecular structure, shows the best performance by utilizing the planar mixed heterojunction (PMHJ) structure. The optimized blend ratio is DT4MIDTP:C70 = 1:1 (by volume), giving a PCE of up to 4.22 %. The PCE further improves to 4.6 % by utilizing the tandem PMHJ structure. The electrical and optical properties of DT4TIDTP and DT4MIDTP films after thermal annealing are also investigated. With appropriate pre-annealing treatment, the performance of DT4MIDTP device with planar heterojunction structure improves from 1.3 % to 2.5 %. DTPTtDCV, a donor with oligothiophene core, shows the most promising characteristics among all oligothiophene core donor systems in this study with best PCE up to 3.02 %.
In the last part of this thesis, by the aid of our home-made optical simulation program, micro-cavity organic photodetectors (OPDs) with high photoresponsitivity across the entire visible region are demonstrated. In order to enhance the photoresponse of a particular wavelength region, the thicknesses of transparent anti-reflection layers and hole transporting layers are modeled and designed. The OPDs with enhanced photoresponse at target wavelengths are realized. Finally, an in-situ all-vacuum-deposition method to fabricate controllable periodic wrinkling surfaces is demonstrated. By utilizing these wrinkling surfaces as light trapping and light scattering layer in organic optoelectronics, efficient devices with enhanced light in-coupling/out-coupling efficiency are demonstrated.

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