Flexible And Low Voltage Organic Field-effect Transistors With PAA As Dielectric Layer

Organic field-effect transistors(OFETs)have potential application value in the field of flexible electronics because of their advantages of low cost,simple preparation process,solution processing and compatibility with flexible substrates.At present,the mobility of organic semiconductors has far exceeded 10 cm~2/(V·s),reaching the level of practical application.But devices such as wearable electronics and flexible sensors need to operate at low voltages,which negatively impact their security and power consumption.Polyelectrolyte can produce large capacitance,which can effectively reduce the operating voltage of the transistors.In this thesis,polyacrylic acid(PAA)was used as the research object to prepare flexible transistors with low voltage and high mobility.On this basis,polymethyl methacrylate(PMMA)was used to further improve its dielectric properties,and its mechanical stability was studied under bending conditions.In the first part,we prepare rigid and flexible field-effect transistors using single layer PAA as dielectric layer,and test their mechanical stability.Firstly,the flexible pentacene transistor was prepared by vacuum evaporation.The mobility of the transistor was 5.03 cm~2/(V·s)and the threshold voltage was-1.42 V.The performance of the transistors can basically reach the level of rigid pentacene devices.Then,the rigid and flexible C8-BTBT transistors were prepared by dip-coating method.The device mobility was 9.2 cm~2/(V·s),the threshold voltage was-1.4 V,and the switching ratio was 10~4.The performance of the C8-BTBT transistors reached the level of the rigid substrate devices.The mechanical stability of the transistor was tested.Although the performance of the transistor decreases to a certain extent,it still shows good transistor operation under low voltage.In the second part,PMMA was used to further improve the dielectric properties of bare PAA,and high performance flexible organic transistors with double dielectric layers are prepared.The switching ratio of the double-dielectric layer pentacene transistor was an order of magnitude larger than that of the single-dielectric layer device.The device reached saturation at the operating voltage of-5 V,and the mobility increases to 6.24 cm~2/(V·s),and the threshold voltage was-2.29 V.By exchanging the spin coating sequence of the dielectric layer,pentacene transistors with a mobility of8.74 cm~2/(V·s)were obtained.In C8-BTBT transistors,the vertical phase separation method was used to further improve the dielectric properties of the single-layer PAA.The C8-BTBT transistor was saturated in the operating range of-5 V,increasing its switching ratio by two orders of magnitude compared to a single layer PAA dielectric layer transistor,resulting in a significant improvement in performance,with a mobility of 35.3 cm~2/(V·s),and a threshold voltage of-1.49 V.In the third part,in order to further characterize the flexibility of the device,we conducted mechanical stability tests on pentacene transistors and C8-BTBT transistors,respectively.When the pentacene device was bent in the vertical channel direction and the strain was 1.25%,its performance decreased by 31.7%of the initial value,when it was bent in the parallel channel direction and the strain was 1.25%,its performance decreased by 24.6%of the initial value.When the C8-BTBT device was bent in the vertical channel direction and the strain increased to 1.25%,the mobility decreased by48.4%.When bent in the parallel channel direction,the mobility decreased by 32.9%.After multiple bends based on small radius,the performance of the flexible transistors has decreased to varying degrees.Compared with the parallel channel bending,the degradation in the vertical direction is more serious.However,all devices can be opened in the range of-5 V under the bending state,showing good operating stability at low voltage.