Over 30% external quantum efficiency for doping-free D-A-type thermally activated delayed fluorescence organic light-emitting diodes

The application of doping-free emitting layers in organic light-emitting diodes (OLEDs) device fabrication has attracted extensive attention due to the simplified process and the low cost. Meanwhile, the application of interfacially doping layer (or ultrathin emissive layer, UEML) with a thickness below 1 nm showed great potential in achieving high device efficiency by reducing the aggregation-caused quenching (ACQ) effect, which was usually observed in neat film and highly doped dopant-host system. This work developed a simple molecular design strategy via peripheral decoration of TADF emissive core with multiple shielding groups (t-butyl and aryl units) to effectively alleviate the intermolecular interaction and the ACQ effect. The resulting OLEDs based on BIPH-TPA exhibited a record-setting external quantum efficiency (EQE) of 15.8 % at 640 nm with a conventional doping-free configuration (25 nm). Furthermore, the ultrathin doping-free (0.2 nm) OLEDs based on NA-TPA achieved unprecedented EQE of 33.1 % at 620 nm. The outstanding EL performance clearly demonstrated promising potential of this molecular design strategy for the exploration of doping-free OLEDs.