Enhancing the efficiency of alternating current driven organic light-emitting devices by optimizing the operation frequency

We report efficient and bright organic light-emitting devices operated by capacitive energy coupling. In this approach, the organic layers are enclosed between sputter-deposited hafnium dioxide layers to prevent charge carrier injection. When a sinusoidal voltage signal is applied to the electrodes, the devices emit bright green light whereas no detectable emission is generated upon application of a constant voltage. The efficiency of the process depends heavily on the frequency of the applied voltage signal. By optimizing the driving scheme, a record luminous efficacy for AC driven OLEDs of 2.7 lm/W at 500 cd/m2 is achieved.

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► Organic light-emitting devices operated by capacitive energy coupling were investigated.
► Insulating layers of hafnium dioxide prevent charge injection into the device.
► A constant DC voltage leads to no detectable light emission.
► Applying a sinusoidal driving voltage results in bright green light emission.
► We show that tuning the driving frequency greatly effects device efficiency.