| Organic field-effect transistors（OFETs）are a significant class of low-cost electronic devices with advantages such as lightweight,easy processing,and excellent signal amplification capabilities,showing great potential for a wide range of applications in the fields of information technology,sensing,and biomedical engineering.In recent years,the rapid development of OFETs has greatly promoted device mobility comparable to that of polysilicon,which can meet the requirements of logic circuit applications.However,organic materials used in OFETs are susceptible to environmental factors such as light,moisture,oxygen,and temperature,ultimately leading to unstable performance and limited practical applications.Additionally,organic materials degrade over time,resulting in a shorter lifetime for OFETs and further hindering their commercialization.To address these problems,this dissertation employs two strategies to improve the semiconductor layer and the dielectric layer of OFETs,and focuses on the achievement of flexible OFETs with high electrical performance and good stability.Subsequently,the dissertation explores different sensing applications based on these highly stable OFETs.The main contents of this dissertation include the following four sections:First,a series of solution-processed novel semiconductor heterostructured films were developed using the p-type conjugated polymer semiconductor PCDTFBT and the insulating material polystyrene（PS）.By controlling the PS content in the films,the short-range ordering of PCDTFBT was maintained to ensure effective intermolecular charge transfer for the high mobility of flexible OFETs.Simultaneously,the long-range ordering of PCDTFBT was suppressed to reduce leakage currents induced by its intrinsically high conductance and enhance the OFET switching ratio.Various characterization techniques elucidated that the formation of a highly compatible,cross-interconnected reticulated nanoheterostructure of the two-phase polymer materials on the film’s surface and inside is the key to the achievement of high-performance OFETs.The PCDTFBT:PS film-based OFETs showed excellent photostability,with only approximately 3%open-state current fluctuation under multiple laser irradiation.Furthermore,the devices exhibited long-term air stability after exposure to high-humidity air for over 450 days.Secondly,a series of solution-processed PS passivation layer films were developed to modify the polyelectrolyte composite dielectric layer consisting of polyacrylic acid（PAA）and polyethylene glycol（PEG）.By controlling the thickness of the PS interface passivation layer,flexible OFETs with low-operating voltages and high mobilities can be achieved by blocking ion migration generated from hygroscopic PAA:PEG.This passivation was achieved without obviously affecting the double electric layer effect of polyelectrolytes,thus eliminating the impact of electrochemical doping on the semiconductor channel.Furthermore,the PS passivation layer can reduce leakage currents of the polyelectrolyte material and improve the OFET switching ratios.The transfer and output characteristic curves of the OFETs showed a minimal hysteresis effect,with nearly overlapped curves during the forward and reverse scanning.The operational stability of the OFETs was also greatly improved,as the impact of the gate voltage scanning rate has significantly reduced.Thirdly,with the use of an optimized PS passivation layer,a gate-suspended structure for a flexible OFET sensor was designed.By suspending the gate on top of the PAA:PEG dielectric layer,a tiny air gap was formed.It can be seen that different pressures can alter the contact between the gate and the dielectric layer,resulting in a change in device capacitance and pressure response.The suspended structure enabled the OFET pressure sensor to be highly sensitive up to 897.9 k Pa-1,with a low detection limit and fast response.The OFET pressure sensor can monitor the real-time bending rate of the human arm,exhibiting good cyclic stability during different bending conditions.Additionally,the integrated OFET sensor array can achieve high-resolution 2D mapping of pressure imaging.Lastly,based on the optimized PS passivation layer,a flexible optoelectronic OFET synapse with PCDTFBT as a photosensitive layer was developed.The broad spectral properties of PCDTFBT were utilized to make the optoelectronic synaptic device in response to multiple wavelengths of light.By adjusting the characteristics of light pulses,the OFET-based synapse was capable of reproducing some basic functions of biological synapses,including excitatory postsynaptic current（EPSC）,double-pulse facilitation（PPF）,short-term memory（STM）,and long-term memory（LTM）.Through the adjustment of gate voltages and source-drain voltages,the synaptic device can elicit an excitatory response to different light wavelengths.The parameters of such a synaptic device can be modeled to achieve the application in high-pass filters and convolutional neural networks.Moreover,a large-area synaptic OFET array was successfully prepared to facilitate learning and forgetting of patterned light pulses. |
