Fabrication Of High-performance Organic Field-Effect Transistor Arrays Based On Screen Printing

Organic field-effect transistors(OFETs)are one of the most important elementary electronic devices,which have shown great potential in electronic applications,such as flexible displays,integrated circuits,and sensors.In contrast with inorganic thin film transistors,OFET can be fabricated in lower temperature and onto flexible substrates.As the key part of OFET,organic semiconductor film with suitable thickness and highly ordered molecular packing is always preferred for carrier injection and transport.So far,various solution based methods have been developed to fabricate high-quality organic semiconductor thin films,such as inkjet printing,spray printing,and screen printing.Among these methods,screen printing is considered as a low-cost,simple,and efficient method to fabricate electronic devices in industry.Due to the requirement of high viscosity of ink,the thickness of the printed film is about several microns,which is not conducive to carrier injection.Therefore,it remains a significant challenge to fabricate high-performance organic small molecule semiconductor thin film by screen printing.In this thesis,we focused on the fabrication of high-performance OFET by screen printing and carried out a systematic study on the fabrication process.The main conclusion are obtained as follows:1.We employed a protocol of C₆-DPA blending with insulating polymer to improve the wettability on the Si O₂/Si and the crystalline of C₆-DPA films.A relatively uniform C₆-DPA film is obtained and its thickness is about 20 nm.The OFET device is fabricated based on the printed C₆-DPA film,and the highest mobility is 2.5 cm²V^-1s^-1.Due to the high defect density presented in printed C₆-DPA film,the performance of printed device is obviously lower than its single crystal devices.We added F₄-TCNQ into C₆-DPA with PMMA mixed solution as the dopant to further improve the device performance.As a result,the optimized device mobility is up to 5.0 cm²V^-1s^-1,which is consistent with the reported C₆-DPA single crystal device performance.We also prepared the C₈-BTBT films by screen printing,the highest mobility of C₈-BTBT devices is up to 7.8 cm²V^-1s^-1.2.We used an insoluble bank to constrain the size of thin film and improve the crystallinity.Based on the optimum parameters,we fabricated highly crystalline C₆-DPA and C₈-BTBT thin film array,and the highest mobility are about 1.84 cm²V^-1s^-1and 12.1 cm²V^-1s^-1,respectively.Finally,a highly crystalline C₈-BTBT film array was fabricated on a flexible PEN substrate,the hole mobility of devices is up to 2.56 cm²V^-1s-1.3.We developed a two steps printing method to prepare highly oriented organic single crystal array.The highest mobility of the patterned C8-BTBT single crystal obtained is 10.7 cm² V^-1 s^-1,a high on/off ratio is 10⁹,a steep subthreshold swing is 0.23V dec^-1,and a small threshold voltage is-5 V.To demonstrate the application of patterned OSC thin film,we fabricated a C₈-BTBT single crystal pseudo-CMOS inverter device consist of 4 p-type OFETs,the maximum voltage gain is up to 31.2.These excellent electrical characteristics demonstrate that the patterned domains are high quality OSCs.