Research paper: Drift-diffusion modeling of blue OLED degradation

Scientific Summary

This study addresses the critical challenge of rapid degradation in blue organic light-emitting diodes (OLEDs), often attributed to bimolecular exciton annihilation reactions. The main goal was to implement a rigorous drift-diffusion model to simulate blue OLED degradation due to exciton-polaron annihilation and compare its results to simplified analytical rate equation models. Using the commercial OLED device simulator SETFOS, researchers found that while rate models provide functionally similar results for quantum efficiency roll-off and luminance fade, they are quantitatively different from drift-diffusion simulations unless "effective values" are used for degradation parameters, which absorb the rate model's deficiencies. Crucially, the SETFOS-based drift-diffusion model revealed that trap state defects formed in the emissive layer (EML) cause only a minor voltage increase, whereas defects in the transport layers (e.g., HTL) lead to a significantly larger voltage rise, consistent with experimental observations. This indicates that OLED luminance loss and voltage rise largely stem from distinct sets of defect states forming in the emissive and transport layers, respectively.

Why it matters

These findings are highly relevant to improving blue OLED reliability, which remains a key bottleneck for display and lighting applications. By highlighting the limitations of simplified degradation models and demonstrating the distinct origins of luminance loss (EML defects) and voltage rise (transport layer defects), this research provides crucial insights for advanced material and device design. This deeper understanding can guide the development of more stable and efficient blue OLEDs.

Publication details

Pizano, A., Lampande, R., Cawthorn, R., & Giebink, N. C. (2025). Drift-diffusion modeling of blue OLED degradation. Synthetic Metals, 311, 117797. https://doi.org/10.1016/j.synthmet.2024.117797.

Fluxim tools used

The study extensively used the simulation software SETFOS to implement its rigorous drift-diffusion degradation model. SETFOS was initially employed to calculate the electroluminescence-current-voltage characteristics and the electron, hole, and exciton densities within the device structure. A Python script was then used to iteratively update the SETFOS model with position-dependent defect densities (calculated from exciton-polaron annihilation rates) over degradation time steps. This allowed for the accurate determination of luminance fade (proportional to internal quantum efficiency) and voltage increase at constant current density. This iterative approach ensures that the evolution of charge and exciton densities in response to growing trap concentrations is accounted for, which is critical for accurate degradation modelling. The key benefit of using SETFOS is its ability to rigorously simulate all layers of the device and precisely model exciton and charge carrier densities, overcoming the phenomenological approximations and layer neglect of simpler rate equation models. This advanced capability allowed the researchers to uncover the distinct origins of luminance loss and voltage rise, a critical finding for OLED development.