Interface Engineering For Flexible Organic Field-effect Transistors

Heterogeneous interfaces that are ubiquitous in optoelectronic devices play a key role in the device performance and have led to the prosperity of today's microelectronics.Interface engineering provides an effective and promising approach to the enhancement of the device performance of organic field-effect transistors(OFETs)and even the development of new functionalities.At present,self-assembled monolayers(SAMs)have been widely used to modify the key interface of organic field-effect transistors.However,the shortcomings of the two-dimensional molecular monolayer fabrication process limit the further improvement of the performance of organic field-effect transistors.For example,the fabrication process is not versatile for self-assembled molecules and the interface to be modified,and the quality of the molecular monolayer is uneven.This thesis conducts innovative research on the shortcomings of traditional interface modification methods that have been applied to the interface engineering of OFETs.The main work of this master's thesis includes the following three aspects:1)We developed a self-assembled method of amphiphilic small molecules on the water surface,named solvent surface tension balance(SSTB).By this method,the membrane pressure of the two-dimensional molecular monolayer is driven by the difference in surface tension between the organic solvent and water instead of the physical film balance in the traditional Langmuir-Blodgett(LB)technique.We demonstrated the successful preparation of molecular monolayers based on four amphiphilic small molecules.Compared with the traditional molecular monolayer preparation approaches,this method is very simple and versatile,and has the potential to help us develop a new generation of high-performance electronic technology based on molecular two-dimensional materials.2)We applied multiple two-dimensional molecular monolayers prepared by SSTB to modify the key interfaces in OFETs,i.e.,the dielectric layer/semiconductor interface and the electrode/semiconductor interface.Taking the monolayer of octadecyltrichlorosilane(ODTS)to modify the silica/pentacene and gold/pentacene interface as an example,the average values of the mobilities of the fabricated bottom-gate top-contact and bottom-gate bottom-contact OFETs are 6.16 cm² V^–1 s^–1and 1.02 cm² V^–1 s^–1,respectively.The device performance is higher than that by traditional liquid immersion method,which is one of the best results reported in the literature.In addition,the field-effect mobilities of both p-and n-type semiconductors displayed dramatic improvements of 1–3 orders of magnitude on SSTB-derived ODTS monolayer.For example,pentacene-based and PTCDI-C8-based(N,N'-dioctyl-3,4,9,10-perylenedicarboximide)bottom-gate top-contact OFETs show the highest mobility values of 6.83 cm² V^–1 s^–1 and 0.77 cm² V^–1 s^–1,respectively.3)The obtained molecular monolayers made by SSTB method can be transferred onto any arbitrary substrate including inorganic materials and metals,as well as flexible polymeric dielectrics.Therefore,this method can be applied to the interface modification of flexible organic electronic devices.In addition,we also combined"microcontact imprinting technology"and"solvent surface tension balance"to successfully print molecular monolayer patterning with high-resolution of up to 1?m on the surface of the silicon wafer.