Unraveling the degradation mechanism of FIrpic based blue OLEDs: I. A theoretical investigation

TL;DR

This paper presents a detailed ab-initio theoretical investigation into the microscopic degradation mechanisms of FIrpic-based blue OLEDs, revealing how triplet excitons facilitate bond breaking and potential degradation pathways.

Contribution

The study introduces a combined static and dynamic simulation approach to understand FIrpic degradation, providing insights into bond breaking and fragment evolution in OLEDs.

Findings

Triplet excitons lower the Ir-N bond breaking barrier.

Bond swapping leads to stable or degraded configurations.

Method applicable to other Ir-complexes for stability estimation.

Abstract

We report a detailed ab-initio study of the of the microscopic degradation mechanism of FIrpic, a popular blue emitter in OLED devices. We simulate the \emph{operando} conditions of FIrpic by adding an electron-hole pair (exciton) to the system. We perform both static calculations with the TDDFT framework and we also simulate the evolution of the system at finite temperature via Car-Parrinello molecular dynamics. We found triplet excitons are very effective in reducing the Ir-N bond breaking barrier of the picolinate moiety. After the first bond breaking, the two oxygen of picolinate swap their position and FIrpic can either remain stable in an "open" configuration, or loose a picolinate fragment, which at a later stage can evolve a CO$_2$ molecule. Our method can be applied to other light emitting Ir-complexes in order to quickly estimate their stability in OLED devices. In Paper~II we complement our theoretical study with a parallel experimental investigation of the key degradation steps of FIrpic in an aged device.