A Comprehensive Model of the Degradation of Organic Light-Emitting Diodes and Application for Efficient Stable Blue Phosphorescent Devices with Reduced Influence of Polarons

TL;DR

This paper introduces a comprehensive model for OLED degradation that accounts for multiple mechanisms, successfully applied to enhance blue phosphorescent OLED stability and efficiency, with experimental validation and new insights into quenching processes.

Contribution

A new comprehensive degradation model for OLEDs that includes all major mechanisms and a novel impurity effect, improving understanding and stability of blue PhOLEDs.

Findings

Model accurately predicts voltage rise and EQE loss.

Quenchers mainly originate from dopant polarons.

Optimizing doping ratio significantly extends OLED lifetime.

Abstract

We present a comprehensive model to analyze, quantitatively, and predict the process of degradation of organic light-emitting diodes (OLEDs) considering all possible degradation mechanisms, i.e., polaron, exciton, exciton-polaron interactions, exciton-exciton interactions, and a newly proposed impurity effect. The loss of efficiency during degradation is presented as a function of quencher density, the density and generation mechanisms of which were extracted using a voltage rise model. The comprehensive model was applied to stable blue phosphorescent OLEDs (PhOLEDs), and the results showed that the model described the voltage rise and external quantum efficiency (EQE) loss very well, and that the quenchers in emitting layer (EML) were mainly generated by dopant polarons. Quencher formation was confirmed from a mass spectrometry. The polaron density per dopant molecule in EML was reduced by controlling the emitter doping ratio, resulting in the highest reported LT50 of 431 hours at an initial brightness of 500 cd/m2 with CIEy<0.25 and high external quantum efficiency (EQE) >18%.