Interfacial chemical reaction and multiple gap state formation on three layer cathode in organic light-emitting diode: Ca/BaF{sub 2}/Alq{sub 3}

Journal Article · Tue Jul 14 00:00:00 EDT 2015 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4926503· OSTI ID:22490785

Kim, Tae Gun; Lee, Hyunbok ^[1]; Yi, Yeonjin ^[2]; Lee, Seung Mi ^[3]

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1. Department of Physics, Kangwon National University, 1 Gangwondaehak-gil, Chuncheon-si, Gangwon-do 200-701 (Korea, Republic of)
2. Institute of Physics and Applied Physics, Yonsei University, 50 Yonsei-ro, Seodaemoon-Gu, Seoul 120-749 (Korea, Republic of)
3. Korea Research Institute of Standards and Science (KRISS), 267 Gajeong-ro, Daejeon 305-340 (Korea, Republic of)

A three layer cathode is a promising stack structure for long lifetime and high efficiency in organic light-emitting diodes. The interfacial chemical reactions and their effects on electronic structures for alkaline-earth metal (Ca, Ba)/Alq{sub 3} [tris(8-hydroxyquinolinato)aluminum] and Ca/BaF{sub 2}/Alq{sub 3} are investigated using in-situ X-ray and ultraviolet photoelectron spectroscopy, as well as molecular model calculation. The BaF{sub 2} interlayer initially prevents direct contact between Alq{sub 3} and the reactive Ca metal, but it is dissociated into Ba and CaF{sub 2} by the addition of Ca. As the Ca thickness increases, the Ca penetrates the interlayer to directly participate in the reaction with the underlying Alq{sub 3}. This series of chemical reactions takes place irrespective of the BaF{sub 2} buffer layer thickness as long as the Ca overlayer thickness is sufficient. The interface reaction between the alkaline-earth metal and Alq{sub 3} generates two energetically separated gap states in a sequential manner. This phenomenon is explained by step-by-step charge transfer from the alkaline-earth metal to the lowest unoccupied molecular orbital states of Alq{sub 3}, forming new occupied states below the Fermi level.

• OSTI ID: 22490785
• Journal Information: Journal of Applied Physics, Vol. 118, Issue 2; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKALINE EARTH METALS
ALUMINIUM
BARIUM FLUORIDES
BUFFERS
CALCIUM FLUORIDES
CATHODES
EFFICIENCY
ELECTRONIC STRUCTURE
FERMI LEVEL
INTERFACES
LAYERS
LIFETIME
LIGHT EMITTING DIODES
MOLECULAR MODELS
MOLECULAR ORBITAL METHOD
PHOTOELECTRON SPECTROSCOPY
THICKNESS
ULTRAVIOLET RADIATION
X RADIATION