title: Solution-processed nickel oxide nanoparticles with NiOOH for hole injection layers of high-efficiency organic light-emitting diodes.
abstract: Nickel oxide (NiOx) nanoparticles (NPs) were synthesized by a solution-based method and NP films were used as hole injection layers (HILs) in organic light-emitting diodes (OLEDs). To evaluate the hole injection functionality of the NiOxNP HIL, we compared the performance of OLEDs with three types of HILs: spin-coated PEDOT:PSS, thermally evaporated HAT-CN, and spin-coated NiOxNP films. The considerably high component ratio of NiOOH on the air-annealed NiOxNP film surface results in an enhanced hole injection functionality even without UV-ozone treatment. Consequently, the OLEDs using the NiOxNP HILs show significantly higher performances than those of the OLEDs using PEDOT:PSS along with a more than doubled lifetime. Moreover, the OLEDs using the NiOxNP layers show higher external quantum efficiency (EQE), and current and power efficiency values than those of the OLEDs using HAT-CN at a high luminance level. Most notably, the device shows considerably higher current and power efficiency values than those of the recently reported state-of-the-art OLEDs using other types of metal-oxide or metal-based HILs.
authors.affiliation: Advanced Display Research Center (ADRC), Department of Information Display, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul 02447, Korea. jjang@khu.ac.kr.
authors.forename: Jeonggi
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Electrical and Computer Engineering, Ajou University, Suwon 16499, Korea and Division of Energy Systems Research, Ajou University, Suwon 16499, Korea.
authors.forename: Hui Joon
authors.initials: HJ
authors.lastname: Park
authors.affiliation: Department of Mechanical Engineering, University of California, Berkeley, California 94720-1740, USA.
authors.forename: Costas P
authors.initials: CP
authors.lastname: Grigoropoulos
authors.affiliation: Department of Mechanical Engineering, Gachon University, Seongnam 13120, Korea. dhl@gachon.ac.kr.
authors.forename: Daeho
authors.identifier: http://orcid.org/0000-0002-8119-9677
authors.initials: D
authors.lastname: Lee
authors.affiliation: Advanced Display Research Center (ADRC), Department of Information Display, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul 02447, Korea. jjang@khu.ac.kr.
authors.forename: Jin
authors.initials: J
authors.lastname: Jang