Device-spectroscopy of magnetic field effects in a polyfluorene organic light-emitting diode

TL;DR

This study uses device-spectroscopy to investigate magnetic field effects in a polyfluorene organic light-emitting diode, revealing how magnetic fields influence exciton and polaron densities and challenging existing models of organic magnetoresistance.

Contribution

It provides direct measurements of exciton and polaron densities under magnetic fields, distinguishing between competing models of organic magnetoresistance.

Findings

Magnetic field increases singlet and triplet exciton densities.

Data contradicts exciton formation and triplet-polaron quenching models.

Conductivity also increases with magnetic field.

Abstract

We perform charge-induced absorption and electroluminescence spectroscopy in a polyfluorene organic magnetoresistive device. Our experiments allow us to measure the singlet exciton, triplet exciton and polaron densities in a live device under an applied magnetic field, and to distinguish between three different models that were proposed to explain organic magnetoresistance. These models are based on different spin-dependent interactions, namely exciton formation, triplet exciton-polaron quenching and bipolaron formation. We show that the singlet exciton, triplet exciton and polaron densities and conductivity all increase with increasing magnetic field. Our data are inconsistent with the exciton formation and triplet-exciton polaron quenching models.