Capacitive Properties Of Organic Semiconductor Devices

Organic semiconductor is one of the most application potential fields in science investigating and industry technology. This thesis mainly considers aspects the capacitance characteristic of organic semiconductor device. After a brief review of some fundamental knowledge of the research history, the carrier injection and transport mechanism in organic semiconductor, experimental details, such as fabrication and measurement processes, are described for possible repeat of our experiments by other people. The main work in this thesis consists of two parts, including experimental investigation on capacitance characteristics of doped OLED and the experimental method on measuring capacitance-voltage relation of device in the discharge process.1. The devices are fabricated via doping same density guest molecules into the emitting layer of classic bilayer OLED at different position, the capacitance-voltage and capacitance-frequency characteristics are measured by admittance spectrum. and the current-voltage-luminescence characteristics and the electroluminescence spectrum are measured, too. These results suggest the relation between the capacitance and the luminescence:offer the key of mechanism on negative capacitance phenomena. Moreover, in order to prove the mechanism of them, we fabricate another group of doped samples with different doping density and measure same capacitance characteristics again. By measuring and analyzing the experimental results, the correctness of the conclusions has been approved.2. Voltage-time and current-voltage characteristics of different single organic layer devices are measured during their transient discharge processes. By modeling these characteristics with an equivalent circuit and analyzing the transient discharge processes accordingly, we derive the capacitance-voltage (C-V) relation for the devices. Capacitance decay with bias is found to emerge in the high voltage region of the derived C-V curves, and its presence is ascribed to the characteristics on capacitance of space charge and geometric capacitance with voltage.