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Investigation of the Charge Balance in Green Phosphorescent Organic Light-Emitting Diodes by Controlling the Mixed Host Emission Layer

Investigation of the Charge Balance in Green Phosphorescent Organic Light-Emitting Diodes by Controlling the Mixed Host Emission Layer

Jeonghyun Lee, Pyungho Choi, Minsoo Kim, Kiwon Lim, Younghwan Hyeon, Soonkon Kim, Kwangjun Koo, Sangsoo Kim, Byoungdeog Choi

J Nanosci Nanotechnol. 2018 Sep 1;18(9):5908-5912.

PMID: 29677715

Abstract:

In this paper, we investigated the use of a mixed host emission layer (MH-EML) in green phosphorescent organic light-emitting diodes (OLEDs). The hole transport type (p-type) material (4,4'-Bis(N-carbazolyl)-1,1'-biphenyl (CBP)) and electron transport type (N-type) material (2,2',2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)) were mixed with different ratios. The electrons were easily injected through the lowest unoccupied molecular orbital (LUMO) of TPBi in the mixed host system. Also, holes were confined in the EML because of the deep highest occupied molecular orbital (HOMO) level of TPBi (6.7 eV). These results indicate that excitons were formed effectively and the recombination zone became wider under a high electric field in MH-EML devices. For these reasons, the lifetime of the MH-OLED device was 1.36 times higher than that of a single host emission layer (SH-EML) device and showed a reduction in Joule heating. Finally, the external quantum efficiency (EQE) roll-off ratio from 1 mA/cm2 to 100 mA/cm2 in the optimized device (30.46%) was 18.12%p lower than that of the SH-EML (48.58%).

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP192198859	TPBi		192198-85-9	Price
AP58328317	4,4′-Bis(N-carbazolyl)-1,1′-biphenyl		58328-31-7	Price

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