Investigating degradation mechanisms in organic light-emitting diodes using operando electrically pumped spectroscopy.

Organic light-emitting diodes (OLEDs) have been analyzed using a variety of techniques, each offering unique insights into their performance and degradation, yet conventional electrical diagnostics such as impedance spectroscopy (IS) provide only limited insight into the microscopic origins of failure. This study presents a comprehensive analysis of OLED degradation by integrating IS with operando electrically pumped spectroscopy (EPS), which enables simultaneous electrical and optical probing under operational bias. OLED devices, including systematically fabricated in-situ and ex-situ samples, were investigated under both pristine and thermally degraded conditions. IS effectively captured electrical trends, but could not pinpoint the specific layers or interfaces responsible for efficiency loss in degraded devices. EPS, combined with single-layer and bilayer film analysis, revealed the dominant role of exciton scattering and energy transfer disruptions within the emissive layer (EML) and at the EML/HTL (hole transport layer) interface. Kinetic modeling and decay-associated spectral analysis further identified ultrafast exciton quenching pathways induced by thermal stress. These findings establish EPS as a powerful diagnostic tool for visualizing exciton dynamics and localizing degradation, thereby contributing to the development of more stable OLED device architectures.