Bipolar dotierbare organische Materialien und organische pn-Homoübergänge
Zusammenfassung der Projektergebnisse
The strong n-doping with Ru(t-but-terpy)2 or NDNl together with the efficient p-dopant allows bipolar doping of large-gap matrices. Thus, we realize organic p-i-n homojunctions of several organic matrices with different energy gaps. Because of the high carrier densities, the Fermi energies in the p- and n-doped layers are experimentally well defined. The energy gap and built-in potential ofthe organic p-i-n homojunctions can thus be precisely determined. From the photovoltaic response of pentacene homojunctions, it can be concluded that the open-circuit voltage in the organic homojunctions is limited by the built-in potential: Photogenerated current with an excess quasi-Fermi splitting cannot be fully converted to the electrical energy. The individual carrier transport properties of electrons and holes are investigated utilizing n-i-n and p-i-p single-carrier organic homojunctions. We observe an influence of electron traps on the transport. The quantitative estimations yield an energy level of -0.63 eV and a total density of 1.5 x 10^16 cm^-3 for the electron deep traps. The electron trapping is considered to be the reason for a monomolecular recombination, which is inferred from the light intensity and temperamre dependence ofthe short-circuit currents. A red phosphorescent OLED is realized employing the exceptionally high built-in voltage of 2.2 V in the Ir(piq)3 p-i-n homojunction, which shows a visible emission around 650 nm with low operation voltages. One of the reasons for the relatively low quanmm efficiency is the unbalanced charge stams at the i-layer. We demonstrate that the p-i-n homojunction can be used to examine the balance of electron and hole current densities. It is found that the electron transport in Ir(piq)3 is much more efficient than the hole transport. The above results support the fact that the organic homojunction can be an archetypical device to investigate fundamental transport properties and the corresponding device performances in organic thin-film applications.
Projektbezogene Publikationen (Auswahl)
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Organic p-i-n homojunctions: Fundamental properties and application in red phosphorescent OLED. 8th European Conference on Molecular electronics. In: Book of Abstracts, p. 74
Kentaro Harada, Ansgar G. Wemer, Olaf Kühl, Martin Pfeiffer, and Karl Leo
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Acridine orange base as a dopant for n doping ofC-60 thinfilms. J. Appl. Phys. 100, 023716 (2006)
Fenghong Li, Martin Pfeiffer, Ansgar Werner, Kentaro Harada, Karl Leo, Naoki Hayashi, Kazuhiko Seki, Xianjie Liu, and Xuan-Duang Dang
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Field-effect mobility in n-doped €60 thin films. Frühjahrstagung der Deutschen Physikalischen Gesellschaft (Dresden, 2006). In: Verhandl. DPG (Poster), p. 99
Kentaro Harada, Fenghong Li, Martin Pfeiffer, Ansgar G. Werner, and Karl Leo
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Ionized impurity scattering in n-doped Ceo thinfilms. Appl. Phys. Lett. 91, 092118 (2007)
Kentaro Harada, Fenghong Li, Bert Maennig, Martin Pfeiffer, and Karl Leo
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Pentacene homojunctions: Electron and hole transport properties and related photovoltaic responses. Phys. Rev. B 77, 195212 (2008)
Kentaro Harada, Moritz Riede, Karl Leo, Olaf R. Hild, and C. Michael Elliott
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Doped organic semiconductors:Physics and applications, lEICE Technical Reports, 2009, p.67
Karl Leo
