有檆el素子における正孔輸送層/発光層界面でのエキシプレックス形成

摘要

有機EL素子では、発光効率を向上させるために、 電荷輸送層（正孔輸送層、電子輸送層）と発光層を積 層した有機多層構造が広く採用されている。これは、 電荷輸送と発光の機能を分離することにより、電極か ら注入された電子と正孔を発光層内で効率的に再結合 させることが可能になるためである。%Multilayer structures composed of emitting and charge transporting layers have been used extensively in organic light-emitting diodes (OLEDs). Although multilayer structures efficiently confine charge carriers and molecular excitons, OLED characteristics are largely affected by the chemical and physical interaction at organic /organic interfaces. One of the important intermolecular interactions observed at organic/organic interfaces is the formation of a charge-transfer excited state complex, namely an exciplex. We investigated exciplex formations between emitting layer (EML) and hole transporting layer (HTL) that have various highest occupied molecular orbital (HOMO) levels. Exciplex formations at HTL/EML interface were strongly dependent on the HOMO levels of HTLs and decreased electroluminescence quantum efficiencies of OLEDs. Additionally, we found that exciplex formations at HTL/EML interface were influenced by the width of electron-hole recombination zone in EML.