Contact Injection into Polymer Light-Emitting Diodes

TL;DR

This paper investigates charge injection mechanisms in polymer light-emitting diodes, highlighting the roles of tunneling into polaron levels, image force, and space charge effects, with a focus on how disorder influences mobility.

Contribution

It provides a detailed analysis of charge injection processes in polymer LEDs, emphasizing the importance of polaron levels and disorder-induced mobility variation.

Findings

Injection at small voltages is dominated by the image force.

At high voltages, space charge effects become significant.

Mobility variation with field due to disorder critically affects I-V characteristics.

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.