Speedup of Dynamic Response of Organic Light-Emitting Diodes

We demonstrate that large-area organic light-emitting diodes (OLEDs) exhibit slow dynamic response due to their capacitor-like behaviors. In particular, the discharge dynamics of large-area OLEDs is observed to be relatively slower, compared with the charge dynamics. To find ways to increase the response speed of large-area OLEDs, we make an in-depth study of transient electroluminescence (EL) of OLEDs in response to voltage pulses (i.e., pulse separation), device configurations (i.e., device length), and various material parameters (e.g., carrier mobility, exciton lifetime, and energy level offset). The EL response speed can be increased by applying high bias voltage and reducing the device length. Meanwhile, the pulse separation affects the response speed of the second pulse. As the pulse separation is decreased, the ratio of the delay time of the second pulse to the delay time of the first pulse is found to be reduced, whereas the ratio of the peak luminance of the second pulse to the peak one of the first pulse is getting increased. We have also shown that the dependence of the delay time on the carrier mobility, exciton lifetime, and energy level offset is less pronounced. This study may provide design guidelines of OLEDs for practical applications including ac-driven displays and next-generation visible-light communications (VLCs).