Organic Semiconductor's Inkjet Printing Process And Its Orientation Mechanism On Asymmetric Structure

Inkjet printing has received much attention by the simple process, low cost and accurate patterning. For the solution method, the directional growth of the organic semiconductor material prepared can improve the performance of organic thin film transistor (OTFT). For principles of orientation controlling, the adjustment of the surface energy can effectively control the drying process of the solution, which provides a new way to improve the performance of bottom-contact OTFTs prepared by inkjet printing.The main research of this paper is to design and construct the asymmetric electrode with different materials, which can induce the directional growth of crystallization to optimize the performance of OTFTs. We studied the specific preparation parameters and methods, its effect on asymmetric electrode induction and the micro - kinetic mechanism.The main contents are as follows:(1) The bottom-contact gold-silver asymmetric electrode device was fabricated. The drying process and the internal flow of the semiconductor ink in the channel of the device were studied. Differential contact-angles (CAs) of the precursor solution on dissimilar metals of Ag and Au would break the overall balance of surface tension/surface energy(SE) at the liquid/air interface in the horizontal direction. We surmise there is a gradient surface tension and as a result the Marangoni flow that favors receding from the less wettable surface of Ag. The asymmetric electrode induces the semiconductor growth across the channel will enhance the charge transport at the channel. We studied the experimental conditions such as substrate temperature, channel length, drop spacing, and analyzed the different influence on film morphology and device performance. The contact resistance of the OTFT device is systematically analyzed, and the significance of crystal growth controlling process is clarified. The OTFTs prepared under optimal conditions have a nearly 2.5-fold increase in mobility relative to the original device. At the same time,the uniformity of multi-device preparation is also enhanced by the controlled growth of the film.(2) The graphene films were prepared by chemical vapor deposition (CVD) method.The process and parameters of the graphene growth were studied. By comparing the morphology and electrical properties of the films,the optimum CH4 gas flux was determined as 20 sccm, the H2 flux was determined as 20 sccm. Raman spectra shows that the graphene films prepared at the optimum conditions are single layer and can be used as device electrode materials. We explored different methods of transferring and patterning graphene electrodes. After analyzing the advantages and disadvantages of each method,we choose the transferring and then etching method to fabricate the bottom-contact gold-graphene asymmetric electrode device. The semiconductor ink forms a crystal that grows across the channel on an asymmetric substrate. In the case where the level of graphene and the semiconductor material does not match well, the optimization of the crystal morphology still makes the device mobility 2 times higher than the original device.In theory,the asymmetric device structure has a good compatibility with other methods which can enhance the performance of OTFTs. Therefore, further research can try to combine asymmetric structure with other methods.