Energy Level Alignment and Band Bending at TPD/Metal Interfaces Studied by Kelvin Probe Method

Naoki HAYASHI  Eisuke ITO  Hisao ISHII  Yukio OUCHI  Kazuhiko SEKI  

IEICE TRANSACTIONS on Electronics   Vol.E83-C   No.7   pp.1009-1011
Publication Date: 2000/07/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section LETTER (Special Issue on Organic Molecular Electronics for the 21st Century)
Category: Electro Luminescence
band bending,  Kelvin probe method,  vacuum level shift,  energy level alignment,  Mott-Schottky model,  

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In order to examine the validity of Mott-Schottky model at organic/metal interfaces, the position of the vacuum level of N,N'-bis(3-methylphenyl)-N,N'-diphenyl -[1,1'-biphenyl]-4,4'-diamine (TPD) film formed on various metal substrates (Au, Cu, Ag, Mg and Ca) was measured as a function of the film-thickness by Kelvin probe method in ultrahigh vacuum (UHV). TPD is a typical hole-injecting material for organic electroluminescent devices. At all the interfaces, sharp shifts of the vacuum level were observed within 1 nm thickness. Further deposition of TPD up to 100 nm did not change the position of the vacuum level indicating no band bending at these interfaces. These findings clearly demonstrate the Fermi level alignment between metal and bulk TPD solid is not established within typical thickness of real devices.