Numerical Analysis of Trap-Induced Negative Capacitance in Organic LightEmitting Diodes
L. S. C. Pingree, B. J. Scott, M. T. Russell, T. J. Marks, M. C. Hersam; Negative capacitance in organic light-emitting diodes. Appl. Phys. Lett. 14 February 2005; 86 (7): 073509. https://doi.org/10.1063/1.1865346
The goal of this study was to investigate how trap-induced negative capacitance (NC) manifests in organic light-emitting diodes (OLEDs), using drift-diffusion simulations combined with impedance spectroscopy (IS) to better understand defect dynamics and device degradation.
Key findings showed that NC in single-layer polymer OLEDs (PLEDs) arises from slow carrier capture and release at deep trap states, with its magnitude depending strongly on trap depth and density. The simulations revealed that NC consistently appears at forward bias for trap depths greater than 0.2 eV, and that higher trap densities increase the intensity of NC. These insights allow NC to be used as a diagnostic tool for tracking trap generation and device aging during operation.
Fluxim’s Setfos software was essential for the drift-diffusion simulations and small-signal analysis (SSA) used in this study. Setfos enabled accurate modeling of both carrier transport and trap dynamics across different injection conditions, validating experimental impedance spectra and providing a powerful, physics-based alternative to simplified equivalent circuit models.
The findings are important because they offer a more robust framework to diagnose and model degradation mechanisms in OLEDs, paving the way for improved device lifetime predictions and more durable organic electronics.