title: Synergetic Influences of Mixed-Host Emitting Layer Structures and Hole Injection Layers on Efficiency and Lifetime of Simplified Phosphorescent Organic Light-Emitting Diodes.
abstract: We used various nondestructive analyses to investigate various host material systems in the emitting layer (EML) of simple-structured, green phosphorescent organic light-emitting diodes (OLEDs) to clarify how the host systems affect its luminous efficiency (LE) and operational stability. An OLED that has a unipolar single-host EML with conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (
  PSS) showed high operating voltage, low LE (∼26.6 cd/A, 13.7 lm/W), and short lifetime (∼4.4 h @ 1000 cd/m(2)). However, the combined use of a gradient mixed-host EML and a molecularly controlled HIL that has increased surface work function (WF) remarkably decreased operating voltage and improved LE (∼68.7 cd/A, 77.0 lm/W) and lifetime (∼70.7 h @ 1000 cd/m(2)). Accumulated charges at the injecting interfaces and formation of a narrow recombination zone close to the interfaces are the major factors that accelerate degradation of charge injection/transport and electroluminescent properties of OLEDs, so achievement of simple-structured OLEDs with high efficiency and long lifetime requires facilitating charge injection and balanced transport into the EML and distributing charge carriers and excitons in EML.
authors.affiliation: Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) , 77 Cheongam-ro, Nam-gu, Pohang, Gyungbuk 790-784, Republic of Korea.
authors.forename: Tae-Hee
authors.initials: TH
authors.lastname: Han
authors.affiliation: Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) , 77 Cheongam-ro, Nam-gu, Pohang, Gyungbuk 790-784, Republic of Korea.
authors.forename: Young-Hoon
authors.initials: YH
authors.lastname: Kim
authors.affiliation: Samsung Display Co., Ltd. , 95 Samsung 2-ro, Giheung-gu, Yongin-city, Gyeonggi-Do 446-711, Republic of Korea.
authors.forename: Myung Hwan
authors.initials: MH
authors.lastname: Kim
authors.affiliation: Samsung Display Co., Ltd. , 95 Samsung 2-ro, Giheung-gu, Yongin-city, Gyeonggi-Do 446-711, Republic of Korea.
authors.forename: Wonjun
authors.initials: W
authors.lastname: Song
authors.affiliation: Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) , 77 Cheongam-ro, Nam-gu, Pohang, Gyungbuk 790-784, Republic of Korea.
authors.forename: Tae-Woo
authors.initials: TW
authors.lastname: Lee
keywords: capacitance−voltage; degradation mechanism; lifetime; mixed host; nondestructive analysis; organic light-emitting diodes; simple structure; transient electroluminescence