Document Detail

Electronic structure of hybrid interfaces for polymer-based electronics.
MedLine Citation:
PMID:  21690980     Owner:  NLM     Status:  In-Data-Review    
The fundamentals of the energy level alignment at anode and cathode electrodes in organic electronics are described. We focus on two different models that treat weakly interacting organic/metal (and organic/organic) interfaces: the induced density of interfacial states model and the so-called integer charge transfer model. The two models are compared and evaluated, mainly using photoelectron spectroscopy data of the energy level alignment of conjugated polymers and molecules at various organic/metal and organic/organic interfaces. We show that two different alignment regimes are generally observed: (i) vacuum level alignment, which corresponds to the lack of vacuum level offsets (Schottky-Mott limit) and hence the lack of charge transfer across the interface, and (ii) Fermi level pinning where the resulting work function of an organic/metal and organic/organic bilayer is independent of the substrate work function and an interface dipole is formed due to charge transfer across the interface. We argue that the experimental results are best described by the integer charge transfer model which predicts the vacuum level alignment when the substrate work function is above the positive charge transfer level and below the negative charge transfer level of the conjugated material. The model further predicts Fermi level pinning to the positive (negative) charge transfer level when the substrate work function is below (above) the positive (negative) charge transfer level. The nature of the integer charge transfer levels depend on the materials system: for conjugated large molecules and polymers, the integer charge transfer states are polarons or bipolarons; for small molecules' highest occupied and lowest unoccupied molecular orbitals and for crystalline systems, the relevant levels are the valence and conduction band edges. Finally, limits and further improvements to the integer charge transfer model are discussed as well as the impact on device design.
M Fahlman; A Crispin; X Crispin; S K M Henze; M P de Jong; W Osikowicz; C Tengstedt; W R Salaneck
Publication Detail:
Type:  Journal Article     Date:  2007-04-04
Journal Detail:
Title:  Journal of physics. Condensed matter : an Institute of Physics journal     Volume:  19     ISSN:  0953-8984     ISO Abbreviation:  J Phys Condens Matter     Publication Date:  2007 May 
Date Detail:
Created Date:  2011-06-21     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101165248     Medline TA:  J Phys Condens Matter     Country:  England    
Other Details:
Languages:  eng     Pagination:  183202     Citation Subset:  -    
Department of Science and Technology, Linköping University, 60174 Norrköping, Sweden.
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