3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP) and 3′,5-di(9H-carbazol-9-yl)-[1,1′-biphenyl]-3-carbonitrile (mCBP-CN) is a stable host that could be used to synthesise several highly stable blue TADF devices.mCBP-CN is a better film morphology and device thermal stability compared to CBP. mCBP-CN is well-fitted for 5,8-bis(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-5,8-dihydroindolo[2,3-c]carbazole (BDpyInCz) having shallow LUMO and the highest occupied molecular orbital (HOMO) because mCBP-CN has an ET-type character with deep LUMO. So the emitting layer composed of mCBP-CN and the highly doped BDpyInCz works like a mixed host system. The electrons are mainly injected into and transported through the ET-type host material. In contrast, a considerable number of holes are probably injected into TADF emitters and transported through the percolation pathway composed of the emitters having a hole transporting (HT)-type character in our device[1].
