Study On The Solution Processed Of Organic Thin-film Transistors

Conducting and semiconducting materials are of paramount importance in the modern electronic industry.Improving the electronic performances of these materials as well as simplifying the process can promote the development of the electronic industry,and even bring the industrial evolution.As more researches were put in the organic materials,the conducting property of the organic was discovered which led to the flourish of the organic electronics and a large amount of functional organic materials were designed and produced.Inkjet printing is a new,non-contact,non-pressure and stencil free printing technology.It is capable of depositing very small ink droplets(volume down to picoliter or even femoliter)on the desired positions.After the solvent evaporation from the ink,thin film is formed.This technology can effectively reduce the material cost.Organic thin-films transistors(OTFT)can be made with low-cost solution based processes including direct printing,inkjet printing and etc..When applying these processes into large area production of circuits,the procedure becomes simpler than when using traditional inorganic semiconductors.Furthermore,using organic materials provides the possibility of producing flexible electronic devices.People are now looking forward to the future of low-cost,large area and printable flexible electronics.Therefore,it is of great practical significance to develop OTFT by solution process.This work focuses on OTFT.We first studied the OTFT device structure by fabricating BG-TC and TG-BC types.For the BG-TC devices,device performances were compared by incorporating different dielectric materials including Al2O3,OTS treated Al2O3 and OTS treated SiO2.For the TG-BC devices,dielectric layers of CTYOP,PMMA and PVP were compared.We have developed a substrate surface treating method to precisely control the ink spreading dynamics on the substrate.Based on this technique,we have successfully achieved a record-high resolution printing.The printed device has a TG-BC structure with PET as a flexible substrate.A hydrophobic PVA layer was employed to flattern the substrate surface and induce contact-line pinning of the printed PEDOT droplet by partial dissolution of PVA.The constrained contact shape of the PEDOT ink enables precise control of the electrode pattern size.Channel length as smaller as 2 ?m was printed.The dielectric layer is PMMA.It is dissolved in butyl acetate so that it won't cause damage to the underlying PDQT.Before printing PEDOT gate,PMMA surface was treated to be more hydrophilic,to form good contact at the electrode.The printed device is thus all-solution processed,all organic,flexible and transparent.The TFT array has good performance uniformity across a large area.The proposed method to achieve highest printing resolution(20~30 ?m)has great potential in in manufacturing large area and low-cost electronic devices.Due to the low conductivity of the pristine PEDOT(2.69 S/cm),the calculated mobitliy of the printed OTFT is low at 10-3.After treating with H2SO4,the conductivity is successfully improved to 5.52 × 102 S/cm.From the UV-vis absoption spectrum,after treatment,the PSS absorption peak becomes significantly weaker,indicating the reduction of the PSS component in the film.The relative increase of PEDOT content leads to a dramatic increase of the conductivity.Employing such treated PEDOT electrodes as the source and drain,we have succefully fabricated all-organic,all-solution processed OTFT device.The mobility increased to 1.36cm2V-1s-1.The improvement can be attributed to the increase of PEDOT's conductivity by 2-3 orders of magnitude.The semiconducting layer morphology in the channel can influence the mobility of a OTFT.To control the morphology,solvent vapor annealing could induce reorientation of the molecules,induce crystallization or phase separation.We have studied solvent vapor annealing based on the interaction between organic semiconductor materials and solvent molecules.With the enhancement of interaction between solvent molecules and PCDTPT molecules,the surface roughness is increased gradually,indicating PCDTPT molecules chains relaxation and rearrangement.,leads to more rough surface.Solvent were methanol,xylene,dichlorobenzene.The highest hole mobility was achieved when using CB solvent annealing at 140 ?C for 1h.The improvement can be attributed to the solvent's strong interaction with the semiconductor,causing molecular reorientation.