Effects of Various Types of Doping on the Electronic Structure of Organic Interfaces
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Effects of Various Types of Doping on the Electronic Structure of Organic Interfaces Kazuhiko Seki1,2, Toshio, Nishi3 , Senku Tanaka3 , Tadanobu Ikame3 , Hisao Ishii4 , and Kaname Kanai3 1
Research Center for Materials Science, Nagoya University, Furocho, Chikusa-ku, Nagoya
464-8602, Japan 2
Research Institute for Advanced Research, Nagoya University, Furocho, Chikusa-ku, Nagoya
464-8602, Japan 3
Department of Chemistry, Graduate School of Science, Nagoya University, Furocho,
Chikusa-ku, Nagoya 464-8602, Japan 4
Research Institute for Electro Communication, Katahira, Aoba-ku, Sendai 980-8577, Japan
ABSTRACT In various organic electronic devices, interfaces formed by organic layers can play important roles.
We have been studying various organic interfaces for clarifying their structure and
electronic structure. In this talk, we will report our recent study of the effect of various types of doping for a variety of dopants – residual impurity, atmospheric gases, and metallic and organic intentional dopants.
In particular, detailed and quantitative information about the effect of
oxygen from the viewpoint of electronic structure was obtained for titanyl phthalocyanine (TiOPc), and the results corresponded well with the recent report of atmospheric effect on orga nic field effect transistor. INTRODUCTION Recently there is rapid development in the field of organic electronic devices such as organic light-emitting diodes (OLEDs), organic solar cells, and organic field-effect transistors (FETs). In many of these devices, various organic/metal and organic/organic interfaces play important roles.
Thus the elucidation of their structure and electronic structure is important for the
elucidation and improvements of these devices.
At the studies of interfaces, we should
discriminate the two regimes: (1) the phenomena right at the interface, such as the energy level alignment within a few molecular layers and formation of electric dipolar layer at the interface, and (2) the effect of contact extending far into the organic layer, such as band bending leading to Fermi level alignment. Usually organic semiconductors are used without intentional doping in
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various organic electronic devices. Thus it is necessary to examine the common assumptions in doped inorganic semiconductor devices such as the band bending leading to Fermi level alignment. As for (1), we have already reported that interfacial dipole layer is formed, usually with the organic side positively charged [1], and this is now well established by the work by us and other workers [2]. Such dipole layer can significantly affect the energy level alignment at the interface, and the origin of such layer has been intensively studied [1-4]. As for (2), we have reported that the alignment of the metal Fermi level with that of organic layer pinned at fixed energy is not established for well purified materials (e.g. TPD and p-sexiphenyl) under ultrahigh vacuum (UHV) conditions [5-7]. On the other hand, in some cases (e.g. C60 ), such alignment is e
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