Study On The Preparation Of Organic Electrochemical Transistors By AC Bipolar Electrodeposition

Organic Electrochemical Transistor(OECT)has been widely used in many fields since it was first reported.It has many advantages.Such as simple manufacturing process,low operating voltage,high sensitivity,and good compatibility with flexible substrates.In this thesis,the OECT arrays was prepared based on alternating current(AC)bipolar electrochemical method.The width and thickness of the organic semiconductor(OS)film and the OECT performance were adjusted by changing the frequency of the alternating voltage.The main work is as follows:(1)AC bipolar electrodeposition method was used to prepare PEDOT:PSS films between microelectrodes with a tip spacing of 10 ?m.The effects of experimental parameters on the morphology of PEDOT:PSS films were explored.By adjusting the driving voltage frequency,PEDOT:PSS films with different widths and thicknesses can be prepared.Their three-dimensional morphology is characterized by atomic force microscope,scanning electron microscope(SEM)and laser microscope.SEM was used to characterize the surface morphology of the PEDOT:PSS film.The results show that as the frequency increases,the film begins to become denser and denser,the surface roughness gradually increases.It's mechanism is explained by Electrochemical impedance spectroscopy(EIS).In addition,the influence of driving voltage amplitude and EDOT monomer concentration on the morphology of PEDOT:PSS film was also investigated.The results show that the amplitude and concentration have little effect on the morphology of PEDOT:PSS film,especially the width and thickness of the film.(2)The cyclic voltammetry was used to analyze the electrochemical process of EDOT monomer polymerization.Two peaks appeared in the cyclic voltammetry curve.The first at 1.15 V was due to the oxidation of EDOT on the electrode surface.The second at 1.40 V is due to the peroxidation of PEDOT on the electrode surface.The current density corresponding to the first peak is approximately linear with the square of the scan rate.This phenomenon indicates that EDOT oxidation process is limited by the mass transfer rate of the reactants in solution(3)According to the previous achievements,an equivalent circuit was proposed.The parameters of the circuit components in the equivalent circuit were determined by EIS.Circuit simulation software(Multisim)was used to calculate the potential distribution at different positions in the experimental setup.The potential was used to explain the mechanism of the driving voltage frequency and amplitude on the morphology of the PEDOT:PSS film.(4)By using the method of alternating current bipolar electrochemi-stry,the preparation of OECT arrays was realized.Their performance is measured by digital source meter.Measurement results show that the performance of OECT arrays have good uniformity.The frequency of the driving voltage is changed to achieve the regulation of the OECT performance.When the frequency of the driving voltage is increased from 50 Hz to 1000 Hz,the maximum sourcr-drain current(Ids)of the OECT decreased from 450 ?A to 160 ?A,the maximum transconductance(gm)decreased from 0.8 mS to 0.15 mS,on/off current ratio(Ion/off)is decreased from 164 to 64,threshold voltage(VT)is reduced from 0.32 V to 0.25 V,time constants for switching-on(?on)is reduced from 75 ms to 22 ms,and time constants for switching-off(?off)is reduced from 227 ms to 126 ms.In order to further explore the mechanism of driving voltage frequency for OECT performance regulation,we associate the performance data of OECT with the size of the OS channel layer.The results show that gm,Ion/off was proportional to W·D/L,VT was proportional to D,?on and ?off were directly proportional to D·(?).The change of VT is weak with the increase of D,the amount of change is only 0.07 V.