Evolution of luminance by voltage in organic light-emitting diodes

We study degradation behaviors of luminance and voltage in organic light-emitting diodes. We find that normalized luminance and inverse normalized voltage with time, $L(t)$ and $V(t)−1$⁠, follow the stretched exponential decay. On this basis, we derive a general relation of luminance and voltage with time as $L(t)=V(t)−δ(t)$⁠, where $δ(t)$ indicates a decay exponent, which is attributed to time-dependent space-charge limitation. Here the observation of higher $δ(t)$ at higher initial luminance explains why luminance decay is faster at higher initial luminance.