Special Section on Organic Photovoltaics

Electronic structure of molybdenum-oxide films and associated charge injection mechanisms in organic devices

[+] Author Affiliations
Jens Meyer, Antoine Kahn

Princeton University, Department of Electrical Engineering, Princeton, New Jersey, 08544

J. Photon. Energy. 1(1), 011109 (March 10, 2011). doi:10.1117/1.3555081
History: Received September 15, 2010; Revised January 26, 2011; Accepted January 26, 2011; Published March 10, 2011; Online March 10, 2011
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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.

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© 2011 Society of Photo-Optical Instrumentation Engineers (SPIE)

Citation

Jens Meyer and Antoine Kahn
"Electronic structure of molybdenum-oxide films and associated charge injection mechanisms in organic devices", J. Photon. Energy. 1(1), 011109 (March 10, 2011). ; http://dx.doi.org/10.1117/1.3555081


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