電致螢光有機半導體之光物理

Abstract

我們研究了三個與有機半導體光物理有關的課題：能隙下激發光電流產生機制、藉由磁性摻雜提升電致螢光效益以及可變色多層發光二極體元件模擬。第二章首先回顧了頗受爭議的能隙下光激發光電流實驗。經由深層能階缺陷之俄歇激子解離是為一可能機制。我們也計算了俄歇過程之倒置反應--衝擊離子化。並且提出了運用衝擊離子化過程之單極發光二極體電致螢光發光的可行性。第三章示現了一種提升共軛高分子發光二極體電致螢光發光效益的理論方法。在高分子發光二極體中摻入磁性化合物能夠開啟介於發光單重態激子與非發光三重態激子之間的通道。適當的磁性摻雜濃度，有可能將單重態激子比例從自旋無關的百分之二十五提升上達百分之八十。第四章是多層有機發光二極體的元件模擬。我們提出兩種多層結構，可以在電壓增加時，使發光顏色從橘紅光，變為綠光，再變為藍光。這類結構提供了除了常見的噴墨印表技術以外，另一種利用有機材料達成全彩顯示的具潛力解決方案。

We study three topics on the photo-physics of organic semiconductors:mechanism for photo-current generation for the excitation below the energy gap;electroluminescence yield improvement by magnetic doping; and device simulation for color-tunable multilayer organic light-emitting diode (LED). Chapter 2 first reviews the controversial photo-current induced by photo-excitation below band gap. Auger exciton dissociation through deep level defects was proposed as the possible mechanism. We calculate the inverse process of Auger process, impact ionization, as well. A feasibility of the electroluminescence for unipolar light-emitting diode based on the impact ionization process is presented. Chapter 3 presents a method to improve the electroluminescence efficiency of conjugated polymer LED theoretically. Doping magnetic complexes into polymer LED can turn on the transition channel between radiative singlet exciton and nonradiative triplet exciton. With suitable concentration for the doped magnetic complexes, it is possible for the singlet exciton ratio being beyond the spin independent value 25% and reach up to 80%. Chapter 4 presents device simulation for multilayer organic LED. Two device structures are shown to have the possibility to tune the luminescence color from orange-red, green, then to blue as the bias voltage increases. These structures provide a potential solution for full-color display with organic material other than the common technology by ink-jet printing method.