Elucidation of the mechanism of organic EL devices

有机EL器件具有叠层薄层结构。电致发光器件中各层之间的界面对器件的性能有很大的影响。因此，我们调查的有机EL器件的机制，奠定了重点的界面的影响。(1)电子从阴极注入：电子从阴极注入到铝-羟基喹啉层中，该层是发光材料。为了研究电子注入机制，制备了具有金属/ALQ/金属结构的样品。通过分析不同温度下的I-V特性，将电子注入归因于肖特基发射，并通过详细分析电流的温度依赖性，确定了ALQ与镁（阴极）之间的势垒高度为0.58 eV。(2)从ITO的空穴注入：还研究了从ITO到作为空穴传输材料的二胺化合物层的空穴注入。从结果中发现，空穴也是通过肖特基发射机制注入的。ITO和二胺层之间的势垒高度被确定为0.41eV。(3)ALQ和空穴传输层之间的界面对EL效率的影响：由于薄层结构，很难确定EL发射的量子效率。因此，我们通过比较光致发光（PL）和EL发射的强度来研究EL发射的效率。从结果中我们发现，EL效率是PL效率的13%。低的EL效率归因于电子和空穴在ALQ/空穴传输层界面处的直接复合。

Organic EL devices have the structure of stacked thin layrs. The interfaces between the layrs affect the properties of the EL devices. We therefore surveyed the mechanisms of the organic EL devices, laying stress on the effects of the interfaces.(1) Electron injection from the cathode :Electrons are injected from the cathode into the layr of aluminum-hydroxyquinoline, which is the light emitting material. In order to study the electron injection mechanism, samples having the structure of metal/ALQ/metal were prepared. From the analysis of the I-V characteristics at different temperatures, the electron injection is assigned to the Schottky emission.From the detailed analysis of the temperature dependence of the current, the energy barrier height between ALQ and magnesium (cathode) was determined to be 0.58 eV.(2) Hole injection from ITO :The hole injection from ITO into the layr of a diamine compound, which is the hole transporting material, was also studied. From the results it was found that the holes are also injected by the Schottky emission mechanism. The barrier height between ITO and the diamine layr was determined to be 0.41 eV.(3) Effect of the interface between ALQ and hole transporting layrs on the EL efficiency :It is difficult to determine the quantum efficiency of the EL emission because of the thin layr structure. We therefore studied the efficiency of the EL emission by comparing the intensities of photoluminescence (PL) and EL emissions. From the results, we found that the EL efficiency was 13 % of the PL efficiency. The low EL efficiency was attributed to the direct recombination of electrons and holes at the ALQ/hole transporting layr interface.