Studies On Schottky Gate Static Induction Type Organic Light-emitting Transistors Based On NPB Films

A static induction type organic light-emitting transistor (SIT-OLET) is a device that integrates an organic static induction transistor (OSIT) with an organic light-emitting diode (OLED). The gate can be used to control the light intensity. A SIT-OLET has advantages such as small channel resistance, fast response, and high luminance efficiency.In this thesis, we fabricated SIT-OLETs based on NPB thin films, and investigated their optical and electrical properties as well as the operating principle. By changing the gate shape, modifying the middle gate, adding hole blocking layer, we analyzed the influences of these factors on the devices with Alq3 as the light-emitting layer.Firstly, we optimized the thickness of the hole transport layer and fabricated a SIT-OLET with the sheet-shape gate. We found its brightness is not enough since the middle gate is not transparent.Secondly, we fabricated two SIT-OLETs with a strip-shape and a mesh-shape gate, respectively. Luminescence intensity increased, but the role of the gate voltage to control current is not ideal. The reason is that the gap distance of the gate wire or hole diameter is too large. The barrier zone is much smaller than the width of the channel. Therefore, the gate voltage will not control the current.To improve optical performance and reduce leakage current of the device, we annealed the middle gate in air at 80℃for 0.5 hr. The on/off current ratio increased from 2.5 to 9. The on/off luminance ratio increased from 5 to 13. In addition, we added an insulating layer lithium fluoride (LiF) between the middle gate and the first layer NPB to reduce the leakage current.The on/off current ratio increased to 14, and the on/off luminance ratio increased to 10.Finally, we added C60 between the light-emitting layer and the drain electrode. It not only acted as an electron transport layer, but also a hole blocking layer. It can balance carriers'transport. The on/off current ratio increased to 47, and the on/off luminance ratio increased to 97.