Electronic structure of molybdenum-oxide films and associated charge injection mechanisms in organic devices
- Princeton Univ., NJ (United States)
We report on the electronic structure of freshly evaporated and air-exposed Molybdenum tri-oxide (MoO3) and the energy-level alignment between this compound and a hole-transport material [e.g., N,N'-diphenyl-N,N'-bis (1-naphthyl)-1,1'-biphenyl-4,4'-diamine (α-NPD)]. Ultraviolet and inverse photoelectron spectroscopy show that freshly evaporated MoO3 exhibits deep-lying electronic states with an electron affinity (EA) of 6.7 eV and ionization energy (IE) of 9.7 eV. Air exposure reduces EA and IE by ~1 eV, to 5.5 and 8.6 eV, respectively, but does not affect the hole-injection efficiency, which is confirmed by device studies. Thus, MoO3 can be applied in low-vacuum environment, which is particularly important for low-cost manufacturing processes. Our findings of the energy-level alignment between MoO3 and α-NPD also leads to a revised interpretation of the charge-injection mechanism, whereby the hole-injection corresponds to an electron extraction from the organic highest-occupied molecular orbital (HOMO) level via the MoO3 conduction band.
- Research Organization:
- Energy Frontier Research Centers (EFRC); Center for Interface Science: Solar Electric Materials (CISSEM)
- Sponsoring Organization:
- USDOE SC Office of Basic Energy Sciences (SC-22)
- DOE Contract Number:
- SC0001084
- OSTI ID:
- 1064880
- Journal Information:
- J. Photonics Energy, Journal Name: J. Photonics Energy Journal Issue: 1 Vol. 1; ISSN 1947-7988
- Country of Publication:
- United States
- Language:
- English
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