Control of Spontaneous Orientation Polarization of Host Layers in Organic Light-Emitting Diodes

Spontaneous orientation polarization (SOP), arising from the partial alignment of permanent dipole moments in organic thin films, is regarded as a crucial factor in enhancing the performance of organic optoelectronic devices. In this study, organic host materials, DPCzBN1, DPCzBN2, and DPCzBN3, were synthesized, and their SOP properties were analyzed. An unusual negative SOP was observed in the DPCzBN3 film, while its counterparts, DPCz, DPCzBN1, and DPCzBN2, showed positive SOP. Further, we found that doping emitter molecules into the DPCz derivatives had an adverse effect on negatively polarized SOP. This finding highlights the significant role of dipole-dipole interactions and glass transition temperature (T_g)-dependent molecular kinetic energy in determining SOP in codeposited films.