Universal energy-level alignment of molecules on metal oxides

Mark T. Greiner, Michael G. Helander, Wing Man Tang, Zhi Bin Wang, Jacky Qiu, Zheng Hong Lu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

869 Citations (Scopus)


Transition-metal oxides improve power conversion efficiencies in organic photovoltaics and are used as low-resistance contacts in organic light-emitting diodes and organic thin-film transistors. What makes metal oxides useful in these technologies is the fact that their chemical and electronic properties can be tuned to enable charge exchange with a wide variety of organic molecules. Although it is known that charge exchange relies on the alignment of donor and acceptor energy levels, the mechanism for level alignment remains under debate. Here, we conclusively establish the principle of energy alignment between oxides and molecules. We observe a universal energy-alignment trend for a set of transition-metal oxidesgrepresenting a broad diversity in electronic propertiesgwith several organic semiconductors. The trend demonstrates that, despite the variance in their electronic properties, oxide energy alignment is governed by one driving force: electron-chemical-potential equilibration. Using a combination of simple thermodynamics, electrostatics and Fermi statistics we derive a mathematical relation that describes the alignment.
Original languageEnglish
Pages (from-to)76-81
Number of pages6
JournalNature Materials
Issue number1
Publication statusPublished - 1 Jan 2012
Externally publishedYes

ASJC Scopus subject areas

  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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