title: Simultaneous Enhancement of Efficiency and Stability of Phosphorescent OLEDs Based on Efficient Förster Energy Transfer from Interface Exciplex.
abstract: Exciplex forming cohosts have been widely adopted in phosphorescent organic light-emitting diodes (PHOLEDs), achieving high efficiency with low roll-off and low driving voltage. However, the influence of the exciplex-forming hosts on the lifetimes of the devices, which is one of the essential characteristics, remains unclear. Here, we compare the influence of the bulk exciplex and interface exciplex on the performances of the devices, demonstrating highly efficient orange PHOLEDs with long lifetime at low dopant concentration by efficient Förster energy transfer from the interface exciplex. A bipolar host, (3'-(4,6-diphenyl-1,3,5-triazin-2-yl)-(1,1'-biphenyl)-3-yl)-9-carbazole (CzTrz), was adopted to combine with a donor molecule, tris(4-(9H-carbazol-9-yl)phenyl)amine (TCTA), to form exciplex. Devices with energy transfer from the interface exciplex achieve lifetime almost 2 orders of magnitude higher than the ones based on bulk exciplex as the host by avoiding the formation of the donor excited states. Moreover, a highest EQE of 27% was obtained at the dopant concentration as low as 3 wt % for a device with interface exciplex, which is favorable for reducing the cost of fabrication. We believe that our work may shed light on future development of ideal OLEDs with high efficiency, long-lifetime, low roll-off and low cost simultaneously.
authors.affiliation: Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University , Beijing 100084, China.
authors.forename: Dongdong
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University , Beijing 100084, China.
authors.forename: Minghan
authors.initials: M
authors.lastname: Cai
authors.affiliation: Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University , Beijing 100084, China.
authors.forename: Yunge
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University , Beijing 100084, China.
authors.forename: Zhengyang
authors.initials: Z
authors.lastname: Bin
authors.affiliation: Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University , Beijing 100084, China.
authors.forename: Deqiang
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University , Beijing 100084, China.
authors.forename: Lian
authors.initials: L
authors.lastname: Duan
keywords: Förster energy transfer; high efficiency; interface exciplex; long operational lifetime; phosphorescent organic light emitting diodes