Oxygen effects on the interfacial electronic structure of titanyl phthalocyanine film: p-Type doping,band bending and Fermi level alignment |
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| Institution: | 1. Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan;2. School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK;3. Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan;4. Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan;1. K.Guminski Department of Theoretical Chemistry, Jagiellonian University, Ingardena 3, 30-060 Cracow, Poland;2. Chemistry Department, Princeton University, 127 Frick Laboratory, Washington Road, Princeton, NJ, USA;3. Physikalisches Institut, Experimentelle Physik II, Am Hubland, Würzburg, D-97074 Germany;1. Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, 1 Seocheon-dong, Yongin, Gyeonggi-do 446-701, Republic of Korea;2. Graduate School of Flexible and Printable Electronics, Polymer Materials Fusion Research Center, Chonbuk National University, 664-14, Deokjin-dong, Deokjin-ku, Jeonju-si, Jeollabuk-do 561-756, Republic of Korea;1. Fujian Key Laboratory of Advanced Materials, College of Materials, Xiamen University, Xiamen 361005, China;2. School of Materials Science and Engineering, Dalian University of Technology, Dalian 116023, China;3. School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China;1. Ioffe Institute, 26 Politekhnicheskaya, 194021 Saint Petersburg, Russia;2. Herzen University, 48 Moika, 191186 Saint Petersburg, Russia;3. Saint Petersburg National Research Academic University, 8/3 Khlopina, 194021 Saint Petersburg, Russia;4. Helmholtz-Zentrum Berlin fur Materialen und Energie, Elektronenspeicherring BESSY II D 12489, Berlin, Germany |
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| Abstract: | The effect of oxygen doping on titanyl phthalocyanine (TiOPc) film was investigated by ultraviolet photoelectron spectroscopy (UPS). The electronic structure of the interface formed between TiOPc films deposited on highly oriented pyrolytic graphite (HOPG) was clearly different between the films prepared in ultrahigh vacuum (UHV) and under O2 atmosphere (1.3 × 10?2 Pa). The film deposited in UHV showed downward band bending characteristic of n-type semiconductor, possibly due to residual impurities working as unintentional n-type dopants. On the other hand, the film deposited under O2 atmosphere showed upward band bending characteristic of p-type semiconductor. Such trends, including the conversion from n- to p-type, are in excellent correspondence with reported field effect transistor characteristics of TiOPc, and clearly demonstrates that bulk TiOPc film was p-doped with oxygen. In order to examine the Fermi level alignment between TiOPc film and the substrate, the energy of the highest occupied molecular orbital (HOMO) of TiOPc relative to the Fermi level of the conductive substrate was determined for various substrates. The alignment between the Fermi level of conductive substrate and Fermi level of TiOPc film at fixed energy in the bandgap was not observed for the TiOPc film prepared in UHV, possibly because of insufficient charge density in the TiOPc film. This situation was drastically changed when the TiOPc film exposed to O2, and clear alignment of the Fermi level fixed at 0.6 eV above the HOMO with the Fermi level of the conducting substrate was observed, probably by p-type doping effect of oxygen. These are the first direct and quantitative information about bulk oxygen doping from the viewpoint of the electronic structure. These results suggest that similar band bending with Fermi level alignment may be also achieved for other organic semiconductors under practical device conditions, and also call for caution at the comparison of experimental results obtained under UHV and ambient atmosphere. |
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