Efficiency Roll-off Suppression in Solution-Processed Organic Light-Emitting Diodes through a Bipolar Host Design

In this study, we address the persistent challenges faced by solution-processed organic light-emitting diodes (s-OLEDs), particularly in terms of low efficiency and significant efficiency roll-off attributed primarily to defects formed during solution processing. Our strategic approach involved the design of three soluble host materials (SiDBFDBA, SiDBTDBA, and SiPhCzDBA) by incorporating a 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (DBA)-based electron acceptor unit, along with electron donor units, namely dibenzofuran (DBF), dibenzothiophene (DBT), and N-phenyl carbazole (PhCz). Notably, the introduction of DBF as an electron donor unit revealed suboptimal electron-donating characteristics, which prompted the incorporation of a p-type host material to achieve a high efficiency of 33.7 cd/A and 23.7%, which is one of the highest EQEs among phosphorescent red s-OLEDs reported. Conversely, DBT and PhCz exhibited enhanced electron-donating effects, which resulted in a significant improvement in efficiency roll-off. Understanding these characteristic distinctions and their correlation with roll-off behavior on the basis of device efficiency provides valuable insights for future directions in creating new hosts to enhance stability.