Exciton and Charge Carrier Interactions in Organic Solid State Films and the Device Application

人们已经认识到使用荧光粉的有机发光二极管(例如。当电流密度大于100 mA/cm2时，由于三重-三重激子的湮没，发光材料的电致发光效率(NEXT)显著降低。除了磷光材料外，荧光材料在高电流密度下的电致发光效率也显著降低。在这项研究中，我们用α-nPd/Alq_3的典型结构阐明了电致荧光器件中的激子湮没过程。在J&lt；100 mA/cm^2的电流密度下，我们观察到η_&lt；Ext&gt；的变化依赖于阴极的配置。在电流密度为100 mA/cm~2时，当电流密度为100 mA/cm~2时，随着电流的增大，空穴和2电子的电荷注入平衡影响了η_&lt；Ext-&gt；的波动，而Flext与电流密度无关。我们将高电流密度下的湮没过程分为三类，单态-单态湮没(SSA)、单态-极化子湮没(SPA)和单态-热湮灭(SHA)模型。

It has been recognized that organic light emitting diodes using phosphors (ex. Ir complexes) demonstrated significant decrease of electroluminescence (EL) efficiency (next) due to the triplet-triplet exciton annihilation at rather high current density over 100mA/cm^2. In addition to the phosphorescence materials, fluorescence materials also show significant decrease of EL efficiency at high current density. However, there are little studies on this subject.In this study, we clarify the exciton annihilation processes in electro-fluorescence devices using a typical OLED structure of α-NPD/Alq_3. At the current density of J<100mA/cm^2 we observed that change of η_<ext> is dependent on the cathode configuration. With efficient electron injection CsAl electrode, flext was independent of current density, whereas flext showed gradual increase with a current increase, suggesting that charge injection balance of hole and 2 electron influences the fluctuation of η_<ext-> Further, at high current density J>100mA/cm^2, flex steeply decreased with a current increase. We classified the annihilation processes at the high current density into three categories, singlet-singlet annihilation (SSA), singlet-polaron annihilation (SPA) and singlet-heat annihilation (SHA) models.