Key Factor Managing the Horizontal Emitting Dipole Orientation of a Thermally Activated Delayed Fluorescence Emitter in a Mixed Host

Horizontal emitting dipole orientation (EDO) of thermally activated delayed fluorescence (TADF) molecules in a mixed host was studied by altering the host materials and host composition of the mixed host to gain insight into the important parameter of the host governing the EDO of TADF emitters. Five different host materials were combined with 1,3-bis(carbazol-9-yl)benzene (mCP), demonstrating that the host-dopant interaction is crucial to the absolute value of the horizontal EDO of the TADF emitters, whereas the glass transition temperature (Tg) is the important parameter determining the EDO dependence upon host composition. The mixed host of mCP with a high Tg host maintained high horizontal EDO in the mCP poor host composition, while that of mCP with a low Tg host showed average horizontal EDO of two hosts. Therefore, the combination of a high Tg n-type host enabling a strong host-dopant interaction with the p-type host with the usage of the n-type-host-rich composition is effective to achieve high horizontal EDO in the mixed-host-based TADF emitting layer.

Automated summary

The orientation of thermally activated delayed fluorescence (TADF) molecules in a mixed host was studied by changing the host materials, revealing that the host-dopant interaction is crucial to the absolute value of the horizontal dipole orientation of the TADF emitters. Additionally, the glass transition temperature plays an important role in the dependence of the dipole orientation on host composition.