Contact injection into polymer light-emitting diodes

Abstract

The variation of current I with voltage V for poly(phenylene vinylene) and other polymer light-emitting diodes has been attributed to carriers tunneling into broad conduction and valence bands. In actuality the electrons and holes tunnel into polaron levels and transport is by hopping among these levels. We show that for small injection the I-V characteristic is determined mainly by the image force, for large injection by space charge effects, but in both cases the strong variation of mobility with field due to disorder plays an important role.

Device physics of single layer organic light-emitting diodes

“…There has been much work done recently to understand the basic principles of organic LED operation. [4][5][6][7][8][9][10][11] Our approach to studying the device physics of organic LEDs is to begin with simple devices in which we can separate, to as large a degree as possible, the fundamental processes of charge injection, transport, and recombination. The understanding gained from the simple devices can then be applied to more complex structures.…”

Contact-Limited Hole Current in Poly(p-phenylenevinylene)

“…For organic semiconductors with an energy distribution of localized states the injection mechanism is expected to be more complicated [14,15]. Alternatively, a model of thermally assisted tunneling of carriers from the contact to localized states of the polymer has been formulated [16].…”

Organic Semiconductor Based Heterostructures for Optoelectronic Devices

“…The electrical transport theories in organics try to describe the charge injection process as thermallyassisted tunnelling from the metal to localized states (Abkowitz, 1995), tunnelling into polaron levels in polymers (Conwell, 1997), thermally-assisted injection into an energetically disordered dielectric (Arkhipov, 1998), or as diffusion-limited thermionic emission (Emtage, 1966;Scott, 1999). The most important factors playing a role in the injection of the charge carriers from metal to organic are the charge mobility in the organic layer (Emtage, 1966;Scott, 1999), the dependence of the mobility of the electric field intensity (Borsenberger, 1998) and of charge density (Roichman, 2002), the trapping of injected charge at the interface due to the image potential (Gartstein, 1996), the interface dipoles arising from the charge transfer (Crispin, 2002) or the interfacial chemistry (Abkowitz, 1998) and disorder in these interface dipoles (Baldo, 2001).…”