Effects of polystyrene on morphology and electrical performance of solution-processed thermally activated delayed fluorescent organic light-emitting diodes

A polymer was added to the emissive-layer (EML) solution of thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs) to enhance their electrical and optical performances. A blue 4CzFCN TADF emitter and m-CBP host were used with 15 wt% dopant, and 1 wt% polystyrene (PS) was added to this EML solution. The PS enhanced the surface morphology, electroluminescence (EL), and external quantum efficiency (EQE). Energy transfer between the host and the dopant material was verified by analyzing the photo-luminescence and time-resolved photoluminescence. After PS treatment, the surface roughness was reduced, according to the root-mean-square value obtained using atomic force microscopy. Finally, we fabricated solution -processed TADF-based OLEDs with an EQE of 4.7% at 7.7 V and a maximum luminance of 3700 cd/m2 at 10 V.