Studies on the structure of the interface between a metal and an organic thin film and voltage-induced processes by using infrared reflection-absorption spectroscopy

为了研究有机发光二极管和有机金属-绝缘体-半导体二极管，我们发展了一种45度入射角的红外反射吸收光谱方法。这些器件具有多层结构，包括金属电极、铟锡氧化物(ITO)电极和有机化合物。在有机电致发光二极管的红外反射吸收光谱中，p偏振态观察到较强的红外带，S偏振态观察到较弱的红外带。对这些结果的解释如下。对于p偏振，入射和反射光束的干涉产生的驻波强度在金属表面的表面法线方向上很强。另一方面，对于S偏振，在金属表面产生的驻波非常弱。通过测量聚合物薄膜的反射吸收光谱和透射吸收光谱，确定了聚合物链的取向。用傅里叶变换红外差光法测量了聚合物发光二极管和聚合物金属绝缘体半导体二极管的电压感生红外吸收光谱。观察到的光谱归因于注入的载流子(极化子)。根据观测结果对聚合物发光二极管的注入载流子平衡进行了讨论。红外反射吸收光谱已被证明是研究有机化合物和有机电子器件中注入载流子的结构和取向的有力工具。

We have developed an infrared reflection-absorption spectroscopic method with a 45 degree incident angle in order to study organic light-emitting diodes and organic metal-insulator-semiconductor diodes. These devices have multilayer structures consisting of a metal electrode, an indium-tin-oxide (ITO) electrode, and organic compounds. In the infrared reflection-absorption spectra of organic light-emitting diodes, infrared bands are strongly observed with the p-polarization and weakly observed with the s-polarization. These results have been explained as follows. For the p-polarization, the intensity of the standing wave produced by the interference of the incident and reflected beams is strong in the direction of the surface normal at the metal surface. On the other hand, for the s-polarization, the resulting standing wave is extremely weak at the metal surface. The orientations of polymer chains have been determined by measuring the reflection-absorption and transmission-absorption spectra of polymer thin films. The voltage-induced infrared absorption spectra of polymer light-emitting diodes and polymer metal-insulator-semiconductor diodes have been measured by using the FT-IR difference spectrum method. The observed spectra have been attributed to injected carriers (polarons). The injected carrier balance of polymer light-emitting diodes have been discussed on the basis of the observed results. It has been demonstrated that infrared reflection-absorption spectroscopy is a powerful tool for studying the structures and orientation of organic compounds and injected carriers in organic electronic devices.