EL Devices from Conjugated Polymers with a High Defect Concentration

1 EL Devices from Conjugated Polymers with a High Defect Concentration 

A conjugated polymer of a high charge carrier concentration (w lo cm arranged between two metal electrodes, can be understood as a MSM structure [40]. 

A semiconductor can be described as a material with a Fermi energy, which typically is located within the energy gap region at any temperature. If a semiconductor is brought into electrical contact with a metal, either an ohmic or a rectifying Schottky contact is formed at the interface. The nature of the contact is determined by the workfunction, 0 (the energetic difference between the Fermi level and the vacuum level), of the semiconductor relative to the metal (if interface effects are neglected - see below) [47]. 

In a first approximation, conjugated polymers with a high charge carrier concentration can be described as B -type semiconductors whereby holes seem to be the majority charge carriers. Depending on the workfunction of the polymer rela- 

In a light-emitting MSM structure the two metal electrodes selected such that the work functions of the electrodes are near the edge of the valence band (VB) and the conducting band (CB) of the semiconductor, respectively, so that oppositely charge carriers are injected from the opposite electrodes. An ohmic and a rectifying contact is therefore formed in the MSM structure (see Fig. 9-22). 

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