Investigation Of Organic Field Effect Transistor Based On Interface Modification & Heterojunction

Organic field effect transistor(OFET)is a research that has received high attention from the scientific and industrial circles today.OFET has good mechanical flexibility,simple preparation process,and is suitable for large-area manufacture.For OFETs,the development of high-performance OFETs is particularly important,and appropriate optimization of the device structure is an effective way to improve the performance of OFETs.In order to obtain a high-performance organic field effect transistor,this dissertation analyzes the influence of the device from the two directions of reducing the interface contact resistance and exploring the introduction of a heterojunction structure.Both pn-type heterojunction and pp-type heterojunction have been series researched.A common method to reduce contact resistance is to match a suitable metal electrode according to the energy level.The most widely used p-type organic semiconductor materials often need to be matched with precious metals such as gold(Au)and platinum(Pt),and their manufacturing costs are relatively high,and they are not suitable for large-scale commercial use.In order to achieve low-cost preparation of high-performance OFETs,this dissertation introduces a modified layer of m-MTDATA between the copper(Cu)electrode and the organic semiconductor material C8-BTBT,which reduces the contact resistance of the device by 90%,thereby increasing the OFET mobility by 10times.Finally,by optimizing the thickness of the modified layer,the C8-BTBT field effect transistor using 20nm thickness m-MTDATA as the hole injection layer achieved a mobility of 1.69 cm²/Vs and a current on/off ratio of 10⁵.At the same time,when the subject was studying the mechanism of the modification layer,it was also found that the introduction of a very thin(2nm)DNTPD between the copper electrode and hexathiophene(?-6T)as a hole injection layer can also play a role in electrode modification.Further research shows that this mechanism is different from the previous m-MTDATA mechanism and belongs to the tunneling effect.On this basis,in order to further improve the device performance,this dissertation uses the C8-BTBT/F16CuPc heterojunction structure to fabricate a dual semiconductor active layer organic field effect transistor,and systematically studies the position and thickness of the heterojunction in the active layer.Performance changes brought about by position and thickness.Through experiments,it is observed that the pn-type heterojunction OFET can indeed obtain a high saturation output current,and the mobility can reach up to 3.02cm²/Vs.However,due to the excessive off-state current,only a value of 10¹-10² of current on/off ratio is obtained.In order to solve the problem of the excessively high off-state current of the device,which is different from the pn-type heterojunction structure,the experiment tried to prepare the organic field effect transistor based on the C8-BTBT/?-6T homotype heterojunction structure.Experimental results show that this pp-type heterojunction device has superior performance.Its maximum on-state current is-515?A,and its off-state current is only-9.8×10^-10A.It has a current on-off ratio of up to 10⁶,and its mobility has also reached 1.01 cm 2/Vs.All devices in this dissertation are prepared based on cheap copper(Cu)electrodes.The proposed methods of reducing contact resistance and adding heterojunctions to improve field-effect mobility have certain guiding significance for practical applications.