Abstract Simplifying device configuration by reducing functional layers and fabrication processes while maintaining high electroluminescence (EL) performance plays an important role in pushing further commercialization of organic light‐emitting diodes (OLEDs). Balanced carrier transport in the emitting layer (EML) is a general prerequisite for simplified devices to achieve comparable EL performances to those of multilayer devices. Herein, a tailored thermally activated delayed fluorescence (TADF) molecule, 10‐(4‐(4,6‐bis(dibenzo b,d furan‐2‐yl)‐1,3,5‐triazin‐2‐yl)phenyl)‐10 H ‐spiroacridine‐9,9′‐fluorene (2FTRZ‐SFAC), with balanced bipolar carrier transport ability is developed. It possesses ultrahigh thermal stability, and exhibits intense sky‐blue emission with a high photoluminescence quantum yield of 99% and a large horizontal dipole ratio of 92.5% in the doped film. 2FTRZ‐SFAC not only realizes an excellent maximum external quantum efficiency (EQE max ) of 36.6% in complex thin‐layer OLEDs, but also attains an outstanding EQE max of 30.6% in simplified thick‐layer OLEDs, which is the best value for thick‐layer OLEDs reported so far. Further, an ultrasmall efficiency roll‐off of 4.7% at 1000 cd m −2 is achieved by optimizing the hole‐injection layer of thick‐layer devices. Such superior EL performance highlights the great potential of simplified thick‐layer OLEDs in display technique, and the gained insights are also conducive to the development of robust bipolar TADF materials for fabricating thick‐layer OLEDs.
Liu et al. (Tue,) studied this question.