Correlation of doping concentration, charge transport of host, and lifetime of thermally activated delayed fluorescent devices

• Lifetime increase in thermally activated delayed fluorescent devices with a unipolar host according to doping concentration.
• Constant lifetime in thermally activated delayed fluorescent device with a bipolar host according to doping concentration.
• Correlation of recombination zone broadening with lifetime of thermally activated delayed fluorescent devices.

Origin of doping concentration dependence of lifetime of thermally activated delayed fluorescent (TADF) devices was examined using a TADF emitter doped in a hole transport type and a bipolar host material. Lifetime of the hole transport type host based TADF device was increased according to doping concentration of TADF emitter, while that of the bipolar host based TADF device was decreased according to doping concentration of TADF emitter. The doping concentration dependence of the lifetime could be correlated with recombination zone of the emitting layer. Broad recombination zone at high doping concentration in the hole transport type host and at low doping concentration in the bipolar host was proposed as the main contributor of the doping concentration dependence of the lifetime.

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