Abstract
Some organic semiconducting materials are spontaneously ordered in evaporated films. We have found that several polar molecules form spontaneous orientation polarization in the evaporated films and it remains in the actual devices. The polarization charge at the organic hetero interface dominates the charge injection and accumulation properties of the multilayer devices. The results are likely extended to many of organic thin film devices if they contain polar molecules. Spontaneous orientation polarization has not been considered as a significant factor to the device performance, though it may be used unintentionally. In terms of the optimization of the device architecture, it should be taken into account as well as the common material properties, such as the energy levels and charge carrier mobility. In this review, we show how the orientation polarization modifies the charge carrier behaviors in the organic light-emitting diodes, particularly focusing on the interface properties.
