氧化鋅奈米柱陣列之製備及其在混成式光電元件與液晶配向之應用

Abstract

本研究之目的為使用水熱法製備ZnO奈米柱陣列，並以其建構混成式光電元件。本研究分為三個部分，第一部分為製備二種晶種層厚度分別為20 nm或48 nm，探究表面形貌與光學特性，再觀測其厚度對於ZnO奈米柱陣列成長之影響。實驗上控制ZnO奈米柱成長時間為20、30及45分鐘，形成之ZnO奈米柱長度分別為150、200及300 nm，直徑則為15-50 nm。所有ZnO奈米柱於可見光光波段之穿透率均大於80%，適合應用於光電元件。 於第二部分中，發光高分子DP6-PPV、MEH-PPV塗佈於ZnO奈米柱陣列基板，以探討ZnO奈米柱結構對高分子光學特性之影響。實驗觀測到DP6-PPV之螢光量子效率因ZnO奈米柱結構的導入而增強； DP6-PPV及MEH-PPV之吸收與螢光放射峰值有藍位移的現象，且DP6-PPV之吸收峰寬大幅減少。上述現象推論為DP6-PPV在ZnO奈米柱結構之堆疊性較平面基板下降，消彌部分薄膜態原有能階躍遷，得以減少吸收峰寬。 於第三部分中，建構結構為ITO/ZnO-rod/P1-BF4/MEH-PPV/ PEDOT/Au之倒置式高分子發光元件，以ZnO奈米柱結構做為電子傳輸層、P1-BF4作為潤濕劑、MEH-PPV作為發光層。最佳元件效果為使用晶種厚度48 nm、長度300 nn之ZnO奈米柱，其元件之驅動電壓、最大亮度及最高效率各為4.2 V、4062 cd/m2及0.57 cd/A (Run 1)或6 V、6791 cd/m2及0.30 cd/A (Run 2)。相較於50 nm ZnO薄膜層製作之元件，以ZnO奈米柱製作之元件效率或亮度顯得較佳，說明ZnO奈米柱結構能夠提升發光元件之表現。 本研究亦利用ZnO奈米柱陣列作為液晶盒之配向層，建構垂直排列模式，於暗態其具備液晶配向特性，證實ZnO奈米柱陣列能夠應用於液晶之配向。

The goal of this research is aimed to prepare ZnO nanorod arrays by hydro-thermal method for construction of hybrid opto-electronic devices. This research is divided into three parts. In the first part, two seed layers with different thickness of 20 or 48 nm were prepared to investigate theirs surface morphologies and optical properties. The influence of thickness of seed layers on ZnO growth was then discussed. The growth time of ZnO nanorod arrays was experimentally controlled to be 20, 30, and 45 min, and the lengths of formed ZnO nanorod arrays were 150, 200, and 300 nm, respectively, with diameters in the range of 15-50 nm. All ZnO nanorod arrays possess transmittance higher than 80% in the visible range, which are suitable for application in opto-electronic devices. In the second part, emissive polymers DP6-PPV or MEH-PPV were deposited on ZnO nanorod arrays to study the effect of ZnO nanorod structure on optical properties of polymers. It was observed that the photoluminescence quantum efficiencies of DP6-PPV were enhanced by ZnO nanorod arrays. Besides, blue shifts in absorption and photoluminescence bands of DP6-PPV and MEH-PPV were showed, and the absorption width of DP6-PPV was narrowed. The above phenomena are resulted from reduced packing of polymers on ZnO nanorod arrays compared with flat substrates, vanishing partial transitions of DP6-PPV to reduce its absorption band. In the third part, inverted polymer light emitting devices with configuration of ITO/ZnO-rod/P1-BF4/MEH-PPV/PEDOT/Au were constructed, using ZnO nanorod arrays as electron transporting layer, P1-BF4 as wetting agent, and MEH-PPV as emissive layer. The best device performance was achieved using 48 nm seed layer and 300 nm ZnO nanorods; the threshold voltage, max brightness, and max efficiency of the devices were 4.2 V, 4062 cd/m2, and 0.57 cd/A in run 1, or 6 V, 6791 cd/m2, and 0.30 cd/A in run 2, respectively. Compared with the device using 50 nm ZnO thin film, the device based on ZnO nanorod arrays showed better efficiency or higher brightness, indicative of significant improvement by incorporating ZnO nanorod arrays. In this research, ZnO nanorod arrays were also used as alignment layers to construct vertical alignment liquid crystal cells. A successful vertical alignment of liquid crystals was observed in dark state, proving the potential applicaition of ZnO nanorod arrays in liquid crystal alignment.