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Displacement Current Measurement for Exploring Charge Carrier Dynamics in Organic Semiconductor Devices
5.1 Introduction
Organic semiconductor (OSC) devices, particularly organic field effect transistors (OFETs), photovoltaic cells (OPVCs), and light-emitting diodes (OLEDs) have been extensively studied in recent decades because of their promising applications in electronics [1–7]. The basic structures of OSC devices were established in the mid-1980s. The first OFETs, composed of small molecules (1984) and polymers (1987), were realized by fabricating a thin OSC layer on a SiO2/doped Si substrate in contact with top or bottom source–drain electrodes [8–10]. In 1986, Tang demonstrated the first efficient OPVC by introducing a bilayer system composed of donor and acceptor layers analogous to the p–n junction used in inorganic devices [11]. The bilayer structure was also applied to OLEDs by Tang and VanSlyke in 1987, significantly enhancing the device performance [12]. These and following works have indicated the importance of developing good interfaces in OSC devices, which has been a key issue in the research in this field. Furthermore, extensive research has been conducted to overcome the interface problems, and resulted in elaborate multilayer structures and various surface treatments in modern OSC devices [4, 6, 7]. The structural optimization of OSC devices has significantly enhanced ...
