Materials World Network: Interdisciplinary Bulk/Surface Studies of Transparent Conducting Oxides

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This is a joint project between Northwestern University (Thomas Mason) and the Technical University of Darmstadt (Andreas Klein) to investigate the bulk vs. surface defect/electronic structure of current and emerging transparent conducting oxides (TCOs). Such materials are employed as transparent electrodes in advanced electro-optic (E-O) devices such as flat-panel displays, light-emitting diodes, and solar cells. Yet little is known about their surface electronic properties (e.g., work functions), which play an important role in establishing potential distributions/band offsets at interfaces with the active semiconductor materials in such applications. For example, indium-tin oxide or ITO, the current workhorse TCO for virtually all E-O applications, is a poor match, chemically and electronically with the HOMO level of the p-type organics used in organic LEDs and photovoltaics. An important outcome of the research will be the collection of much-needed surface electronic property data for ITO-alternative TCOs. At present, there is only a limited literature for the surface electronic properties of the basis TCOs (CdO, ZnO, In2O3, SnO2) and almost nothing is known about the surface properties of the more complex TCOs (binary and ternary compounds and their solid solutions). This interdisciplinary effort combines bulk synthesis and point defect studies at Northwestern University with bulk and thin film photoelectron spectroscopy (XPS/UPS) at the Technical University of Darmstadt. By understanding the correlation between bulk and surface defect/electronic structure, the PIs hope to engineer appropriately doped, well-characterized, and robust TCO electrode surfaces for technologically important E-O applications. This work is co-funded by the Western Europe Program of the NSF Office of International Science and Engineering.