In OLED or multi-layer insulator, two or more polymer dielectrics/or organic materials form the interface. Usually, at the polymer-electrode interface, electric charges are injected following the Schottky thermal injection, Tunneling, or Fowler-Nordheim injection. Then, when an electric field is applied to a polymer-polymer (multi-layer insulator) with different Fermi levels, what principle is the electron injected/transported between the two dielectrics?
Dear Minhee Kim
An electric field can induce several effects in your system depending on its strenght:
1. You start with a multilayered polymer-based system: then LUMO and HOMO levels in each layer are aligned with respect to the other layers, i.e. there are energy bandoffsets between the different layers and consequently there are energy barriers induced by LUMO and HOMO levels alignement at different interfaces.
2. You are dealing with insulating polymers which means that electrons are strongly localized on different LUMO and HOMO levels. The conductivity is negligibly small and the only possible conduction process if any can only be through hopping processes (thermally activated or variable range hopping depending on the degree of localization of electrons).
3. When you apply an electric field to such a system you obtain an effect on each of the two phenomena described above depending on electric field strength:
(i)- the electric field will bend LUMO and HUMO levels in different layers by adding (algebraically) a potential energy to these two levels.
(ii) The energy band lineup may change consequently and the flat bands become triangular bands inducing changes on the dynamics of charge transfer at the interface (e.g. electric field assisted tunneling,...),
(iii) Any free electron (or free charge) will gain kinetic energy from the electric field and will be able to overcome energy barriers at the interfaces.
(iv) any localized electron will be more or less perturbed by the electric field and this may change the hopping conduction processes (electric field assisted hopping)
(v) if the electric field is strong enough, then it will induce strong polarization effects as is the case in dielectrics with consequences on the dielectric functions of your successive materials as well as on electron wavefunctions in different LUMO and HOMO.
Here you have electronic as well as optical properties changes.
See following interesting references:
1. Article Energy Level Modulation of HOMO, LUMO, and Band-Gap in Conju...
2. Article Ultrahigh Discharge Efficiency in Multilayered Polymer Nanoc...
3. Giant Birefringent Optics in Multilayer Polymer Mirrors Michael F. Weber, Carl A. Stover, Larry R. Gilbert, Timothy J. Nevitt, Andrew J. Ouderkirk*
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.945.1762&rep=rep1&type=pdf
Best regards,
Prof. A. Kadri
See following research item related to your topic
https://www.researchgate.net/publication/319499163_Investigation_of_charge_injection_and_transport_behavior_in_multilayer_structure_consisted_of_ferromagnetic_metal_and_organic_polymer_under_external_fields
Ali A. Hameed Abderrahmane Kadri
Thanks for the kind answer.
I think it will be of great help for my research. thank you.
Check https://www.researchgate.net/publication/319697732_Space_charge_mechanism_of_polyethylene_and_polytetrafluoroethylene_by_electrodedielectrics_interface_study_using_quantum_chemical_method
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