A dendrimer emitter doped in a dendrimer host: Efficient thermally activated delayed fluorescence OLEDs with fully-solution processed organic-layers

A thermally activated delayed fluorescence (TADF) carbazole dendrimer (tBuG2TAZ) doped in a carbazole dendrimer host (G3Ph, G4Ph) was employed as an emissive layer (EML) in an OLED device with fully solution processed organic layers. Green (l_MAX = 502 nm) emission with a maximum external efficiency (EQE_MAX) of 16.1% was achieved when tBuG2TAZ was doped in G3Ph. This value was higher than the previously reported OLED device with a neat film of tBuG2TAZ as an EML because of the higher PLQY due to suppressed concentration quenching. The TADF-active carbazole dendrimer doped in a carbazole host film shows excellent miscibility and solvent resistance to ethanol. On the other hand, when a small molecule (rubrene) was doped in the carbazole dendrimer, significant dissolution of rubrene was observed after rinsing the doped film with ethanol. This shows the importance of the solvent resistivity of a dopant emitter when another film is solution-processed onto the doped film. The ''doping dendrimer in dendrimer'' concept is a new concept to allow fabrication of fully solution-processed TADF OLEDs.