Spontaneously Formed Orientation Polarization Thin Films for Engineering Organic-Organic Interfaces

Spontaneous orientation polarization (SOP) of polar molecules is formed in vacuum-deposited films by tilting their permanent dipole moment against the substrate surface direction. In this study, we developed SOP molecules with high structural asymmetry by introducing multiple fluoroalkyl groups into polar molecules because SOP is driven by asymmetric intermolecular interactions on the film surface during the vacuum deposition. The developed polar molecules exhibited high dipole orientation degrees in vacuum-deposited films and achieved a high surface potential growth rate relative to the film thickness, over -350 mV nm^-1, which is a record high for the reported compounds. Furthermore, the dipolar layers introduced at organic thin-film interfaces in hole-only devices and organic photovoltaics to study the impact of dipole interlayers on device performance. The characteristics of the device were observed to be significantly influenced by the SOP polarity, suggesting that the SOP at the organic thin-film interface plays a crucial role in charge transfer and energy level alignment. The findings of this study provide methodologies for the formation of highly anisotropic glassy films, leading to improved performance of organic devices.