Insights into Charge Transport in High-Efficiency Green Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes with a Single Emitting Layer

Simple solution-processed structures of organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) have been demonstrated, but their efficiency and roll-off are still problematic, mainly due to the difficulty in optimizing such device structures. For the first time, solution-processed fabrication of efficient TADF green OLEDs with a simple structure is demonstrated. The emitter 2PXZ-OXD (2,5-bis(4-(10H-phenoxazin-10-yl)phenyl)-1,3,4-oxadiazole) was dispersed in a poly(N-vinylcarbazole)/1,3-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo- 5-yl]benzene (OXD-7) host matrix. Different emitter concentrations (1-10% wt) and different layer thicknesses were applied. Photophysical analysis supports the device structure configuration. The results show a balanced electrical carrier transport, a low turn-on voltage (5 V), an external quantum efficiency (EQE) of 7.5%, and a current efficiency of 16.2 cd/A with a brightness of 7240 cd/m(2). The device exhibited a suppressed roll-off at 1000 cd/m(2) (EQE: 7.15%). Simulations of charge transport properties allowed to explain the results and to optimize, opening interesting frameworks for simple solution-deposited large-area OLEDs.