| 초록 |
Recombination zone using red dopant in mixed host emissive layer was investigated to get high efficiency in green PHOLEDs. We used two types of host materials, which composed of 4,4’,4’-tris(N-carbazolyl)triphenylamine(TCTA) as a hole transport type host with good hole injection and spirobifluorene based PH1 as an election transport type host with good electron properties. Emission zone of PH1 was near hole transport layer(HTL) side in the emitting layer(EML), while that of TCTA was near electron transport layer(ETL) side. Emission zone in mixed host devices became wider than standard single host devices. However, the recombination zone leaned still to HTL side in the EML. The efficiency of triplet mixed host devices improved by more than two times by balancing holes and electrons. We introduced TCTA as an exciton blocking layer between HTL and EML in mixed host devices, which gave high quantum efficiency value of 17.9% compared with 5.8% of TCTA and 3.8% of PH1, respectively. |
