Versatile hole injection of VO2: Energy level alignment at N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine/VO2/fluorine-doped tin oxide |
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| Affiliation: | 1. Institute of Physics and Applied Physics, Yonsei University, 50 Yonsei-ro, Seodaemoon-Gu, Seoul 120-749, Republic of Korea;2. Surface Technology Division, Korea Institute of Materials Science, Changwon 641-831, Republic of Korea;3. Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Republic of Korea;1. School of Engineering and Physical Sciences, James Cook University, Townsville 4811, Queensland, Australia;2. Institute of Materials Research and Engineering, A1STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602, Singapore;3. School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia;4. Centre for Organic Photonics & Electronics (COPE), School of Chemistry and Molecular Biosciences and School of Mathematics and Physics, The University of Queensland, Brisbane 4072, Queensland, Australia;1. Université de Sousse, ISSAT de Sousse, Cité Ettafala, 4003 Ibn Khaldoun Sousse, Tunisia;2. Université de Monastir, LIMA, Faculté des Sciences de Monastir, 5019 Monastir, Tunisia;3. Analytical Laboratory, Department of Applied Organic Chemistry, National Research Centre, Cairo, Egypt;4. Université de Lyon, Lyon1, Institut des Sciences Analytiques (ISA), UMR 5280, 5 Rue de la Doua, 69100 Villeurbanne Cedex, France;1. Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Hubei Key Lab on Organic and Polymeric Optoelectronic Materials, Department of Chemistry, Wuhan University, Wuhan 430072, PR China;2. Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China |
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| Abstract: | Energy level alignments at the interface of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB)/VO2/fluorine-doped tin oxide (FTO) were studied by photoemission spectroscopy. The overall hole injection barrier between FTO and NPB was reduced from 1.38 to 0.59 eV with the insertion of a VO2 hole injection layer. This could allow direct hole injection from FTO to NPB through a shallow valence band of VO2. Surprisingly, VO2 can also act as a charge generation layer due to its small band gap of 0.80 eV. That is, its conduction band is quite close to the Fermi level, and thus electrons can be extracted from the highest occupied molecular orbital (HOMO) of NPB, which is equivalent to hole injection into the NPB HOMO. |
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| Keywords: | Hole injection barrier UPS XPS Energy level alignment Fluorine-doped tin oxide (FTO) |
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