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Study on the Electron Injection Mechanism of Thermally Decomposable Cs2CO3
Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China
(Received June 22, 2009; accepted July 21, 2009; published online October 20, 2009)
Thermally evaporated Cs2CO3 has been reported to be an efficient electron injection material for organic light-emitting diodes (OLEDs) although its electron injection mechanism remains under debate. In this study, we reported a thermodynamic calculation of the decomposition reactions of Cs2CO3, indicating that it is thermodynamically reasonable for Cs2CO3 to decompose into metallic Cs. A thermal decomposition experiment on Cs2CO3 was carried out and the decomposition temperature of Cs2CO3 was found to be close to the calculated temperature at which Cs2CO3 decomposes into metallic Cs. The in situ X-ray photoemission spectroscopy (XPS) profiles showed an agreement between the deposited Cs2CO3 and the standard metallic Cs. The interaction between N and Cs atoms in the Cs2CO3-doped tris(8-hydroxyquinoline) aluminum (Alq3) film was verified by XPS, indicating the existence of Cs. The effect of the oxidizing atmosphere on the electron-only devices has been investigated, and the thermal decomposition of Cs2CO3 into metallic Cs was further confirmed.
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