Abstract
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).
© 2010 IEEE
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