Effects of Molecular Orientation on Stability of Blue Fluorescent OLEDs Based on Hot Exciton Materials

Hot exciton materials have demonstrated significant potential in the fabrication of high-efficiency blue fluorescent organic light-emitting diodes (OLEDs). However, the enhancement of their lifetimes remains a critical challenge. It is well-established that an increase in the horizontal orientation of the emission molecules in the transition dipole moment can enhance the optical coupling efficiency, consequently improving the efficiency of the OLEDs. However, there is little research on the influence of molecular dipole orientation on the stability of blue OLEDs. In this work, we have selected three blue hot exciton organic materials with analogous molecular structures to investigate the relationship between dipole orientation and lifetime of the corresponding blue OLEDs. It is found that the increase of molecular dipole orientation significantly improves the device stability, except device efficiency. The investigations of transient electroluminescence, admittance spectroscopy, and PL decay characteristics demonstrate that high molecular dipole orientation results in a more orderly arrangement of organic molecules, thus greatly reducing the defect density in the emission layer that contributes to the device degradation. This work should be very significant in the design and fabrication of highly efficient and stable hot exciton materials and the corresponding blue fluorescent OLEDs from the perspective of molecular orientation.