Role of Singlet and Triplet Excitons on the Electrical Stability of Polymer Light-Emitting Diodes

Abstract

Stability under electrical stress is an important aspect for the function of organic light-emitting diodes (OLEDs). Degradation is currently one of the key topics in this field, concerning all types of OLEDs, including fluorescent-, phosphorescent-, and thermally activated delayed fluorescence-based OLEDs. For single-layer polymer light-emitting diodes (PLEDs) it has recently been found that degradation is the result of hole trap formation due to exciton–polaron interactions. However, whether singlet or triplet excitons are responsible for degradation is an open question. Here, their contributions are disentangled by systematically manipulating the singlet and triplet exciton populations and their effect on PLED degradation is studied. To control singlet excitons the emission of a blue-emitting PLED is modified to green by adding a small amount of a perylene-monoimide based green-emitting dye. The triplet population is manipulated by blending the light-emitting polymer with a dye that has either a longer or shorter triplet lifetime as compared to the polymer host. The results reveal that the degradation in fluorescent PLEDs is governed by the interaction between polarons and triplet excitons.