探討有機發光電化學元件之離子特性

Abstract

有機發光電化學元件(light-emitting Electrochemical cells, LECs)是目前新興光電元件中極具潛力之新元件，相較於OLED(organic light emitting diode)和PLED(polymer light emitting diode)，LECs具有結構和製程簡單的優勢，因此可大幅降低製造成本，再加上元件材料之特性使其能夠使用在空氣中穩定的金屬做為電極，而成為未來更具廣泛應用的光源。 LECs有機層中的電流是因正、負離子在其中移動所產生，在LECs中有機發光體所發射的光能是來自於其中離子在正負電極上，產生氧化或還原反應所產生的電能。因此各自電極上的氧化還原反應，是有機發光的最基本機制，若要了解這機制必須先了解元件材料的離子特性。為了探討有機發光電化學元件中的離子特性，本論文是世界上首次引入了高、低解離率離子產生和運動方程式，求得有機層中離子之初始濃度、遷移率、結合率、解離率和活化能，利用這些參數可以完整的分析參雜材料的離子特性。進而可以推論離子的化學結構和有機發光分子的結構以及他們之間的關係，最終的目的是，成功開發和製造高發光效率和長壽命的LECs元件，在發光效率和成本上取代OLED和PLED。最後本論文提出了未來研究方向，以解決目前LECs所遇到的發光效率和壽命問題。

Comparing to OLEDs (organic light emitting diodes) and PLEDs (polymer light emitting diodes), light-emitting electrochemical cells(LECs) have advantages of simpler device configuration consisting of an organic thin-film layer between two air-stable electrodes, and capability to emit a broad light spectrum from near infrared to UV light. However, the LECs have disadvantages of short lifetime and lack of understanding on light emitting mechanism in relation to the ionic properties within the cells. The measured currents in the LECs’ organic layers have been the results of drafting ionic molecules under applied external fields within these layers. In LECs, the energy of the emitted light photons comes from the ionic reduction and oxidation (redox) on the negative and positive electrodes, respectively. In order to understand the LECs’ light-emitting mechanism that is correlated with the current, it is advantageous to know the ionic properties within LECs. Based on ion generation and transport equations, we are the first in the word attempting to fit the measured current versus time in terms of field-activated draft of ions from high-ionization- and low-ionization-rate impurities within the LEC cell. From the fitted results, we have obtained the initial ion concentrations, rates of ion dissociation and recombination, and the ion drift mobility as a function of temperature to derive the activation energy of ion-dissociation. By further investigation using the methods reported in the thesis, we hope to identify the chemical structures of ions in relation to the light-emitting mechanism and lifetime of any LEC cell. Finally, we have also pointed out the future directions of research and development to improve the current light-emitting efficiencies and lifetimes of LECs. Our ultimate goal is to develop and manufacture the LECs with high light-emitting efficiency and long lifetime to replace OLEDs and PLEDs for cost saving and green.