Differential capacitance of hybrid organic/inorganic CdSe/ZnS quantum dots light-emitting device
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We have studied the differential capacitance of self-assembly hybrid organic/inorganic quantum dot (QD) light-emitting devices (QD-OLEDs) at room temperature in the frequency range of 1×103 to 1×106 Hz. Self-assembly CdSe/ZnS QDs monolayer was used to fabricate trilayer hybrid QD-OLEDs on indium tin oxide coated glass substrates. We observed negative differential capacitance (NDC) in both OLED and QD-OLEDs for the first time in the intermediate frequency range of 5×103 to 5×105 Hz. The onset and frequency range of NDC are strongly depended on the applied bias voltage. This behavior is described by a mathematical model. The simulated results showed that the NDC was due to the time-dependent transient current from the QDs and organic/metal interfacial states in the device. The probable mechanisms of NDC in organic devices are discussed.