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, <b>DPCzBN1</b>, <b>DPCzBN2</b>, and <b>DPCzBN3</b>, were synthesized, and their SOP properties were analyzed. An unusual negative SOP was observed in the <b>DPCzBN3</b> film, while its counterparts, <b>DPCz</b>, <b>DPCzBN1</b>, and <b>DPCzBN2</b>, 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 (<i>T</i>_g)-dependent molecular kinetic energy in determining SOP in codeposited films.