A polymer was added to the emissive-layer (EML) solution of thermally activated dela yed 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 wit h 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 efficie ncy (EQE). Energy transfer between the host and the dopant material was verified by an alyzing the photoluminescence and time-resolved photoluminescence. After PS treatment, the surface roughness was reduced, according to the root-mean-square value obtained usi ng atomic force microscopy. Finally, we fabricated solution-processed TADF-based OLE Ds with an EQE of 4.7% at 7.7 V and a maximum luminance of 3700 cd/m 2 at 10 V.