Hole limited recombination in polymer light-emitting diodes

Abstract

By comparing the quantum efficiencies of light emission in a series of poly[2-methoxy-5(2 ′ ethyl)hexoxy-phenylenevinylene] diodes with calciumcathodes and various anode metals, we show that, in all cases electrons are the majority carrier and recombination is limited by hole injection. These conclusions are confirmed by the examination of a second series of samples in which alkanethiol barrier layers of varying thickness, are deposited on a goldanode. The highest externalquantum efficiency was achieved in these experiments using a clean, semitransparent goldanode. We suggest that electron and hole injection rates play the primary role in determining current balance and that mobilities play a minor role.