Modification of ITO with Composite Self-Assembled Monolayer Enables Hole Injection and Transport Layer-Free TADF-OLED with Preferable Performance

A complex multilayer device structure severely obstructs the commercial development of thermally activated delayed fluorescence material-based organic light-emitting diodes (TADF-OLEDs) due to high preparation costs. Herein, simplified TADF-OLED without both hole injection layer (HIL) and hole transport layer (HTL) was obtained by embellishing indium tin oxide (ITO) with a composite self-assembled monolayer modification strategy. Perfluorobenzyl phosphoric acid with perfluoroalkyl carboxylic acids formed a denser composite monolayer on the surface of ITO. This increases the work function of ITO, improves the quality of emitting layer film, and facilitates hole injection, which realized direct hole injection without the HIL and HTL. The resultant HIL/HTL-free TADF-OLED gains favorable luminescence performance including a current efficiency (CE) of 76.9 cd A–1 and an external quantum efficiency (EQE) of 22.0% for green TADF-OLED and a CE of 21.4 cd A–1 and EQE of 13.4% for blue TADF-OLED. This work provides an effective method in simplifying TADF-OLED structures for its further commercial application.