Reducing the Efficiency Roll-Off in Organic Light-Emitting Diodes at High Currents under External Magnetic Fields

TL;DR

This paper demonstrates that applying an external magnetic field can partially suppress efficiency loss in high-current organic LEDs by reducing exciton-polaron annihilation, thus improving luminance and device performance.

Contribution

The study introduces a magnetic field approach to mitigate efficiency roll-off in OLEDs by controlling exciton-polaron interactions, a novel method for enhancing high-current device stability.

Findings

Efficiency roll-off is reduced under magnetic fields in Eu3+-based OLEDs.

Luminance is enhanced when magnetic fields are applied.

Magnetic manipulation of polaron-spin and exciton dynamics is effective.

Abstract

Singlet-polaron and triplet-polaron annihilation mechanisms are the most detrimental exciton quenching processes that lower the efficiency of organic light-emitting diodes (OLEDs) at high current densities, causing so-called efficiency roll-off in these devices. These exciton loss mechanisms are also the critical obstacles towards the realization of electrically pumped organic semiconductor lasers, which require very high current densities to reach threshold. Herein, under a relatively large external magnetic field, we demonstrate that the efficiency roll-off at high current densities in europium (Eu3+)-based solution-processed OLEDs can be suppressed to some extent while the luminance is enhanced. We achieve this by reducing the Forster-type exciton-polaron annihilation processes. Under the applied magnetic field, we show that manipulation of the polaron-spin and exciton dynamics lead to a quantitative roll-off suppression.