Fabrication And Characterization Of Doped Devices Based On Bipolar Organic Semiconductors

In recent years,organic semiconductors（OSCs）have been widely used in the field of organic electronics due to their advantages of solution processability,low cost,suitable for the preparation of large-area electronic products and stretchable electronic products.The idea of obtaining p-type and n-type organic semiconductors separately by controllably doping one organi c semiconductor is very attractive,as this not only reduces the cost due to the separate synthesis of different types of OSCs,but also enables to derive some interesting structures,such as homogenous PN junctions,etc.However,the realization of the ab ove ideas faces great challenges due to the difficulty of simultaneously achieving efficient p-type and n-type doping for organic semiconductors.In this thesis,we use the conjugated polymer PBBT-4T-2F with balanced bipolar transport properties as a semico nductor,combined with efficient p-type and n-type dopants,to achieve the first realization of controllable doping to tune organic semiconductors The polarity of the PN junction and the photodetector are constructed on this basis.The specific research contents are as follows:（1）The electrical properties of the bipolar semiconductor PBBT-4T-2F were investigated using an organic field effect transistor（OFET）device,and it was found that the electron and hole mobilities of PBBT-4T-2F were 7.50×10^-3 cm²V^-1s^-1 and 2.08×10^-3 cm²V^-1s^-1,respectively,with highly balanced bipolar transport characteristics,laying the foundation for subsequent p-type and n-type doping regulation.（2）PBBT-4T-2F was doped with high-efficiency p-type dopant Tr TPFB and n-type dopant N-DMBI,respectively,and the doped p-type and n-type semiconductor films were characterized by absorption spectroscopy and electron paramagnetic resonance,confirming the doping effect of the above-mentioned dopants.Using OFET as a platform to study the effect of doping on the electrical properties of semiconductors,it is found that doping can effectively control the polarity of semiconductors:p-type semiconductors are obtained after p-doping,and n-type semiconductors are obtained after n-doping.Then,the effect of doping on the surface morphology and molecular orientation of PBBT-4T-2F films was studied,and the changes of contact resistance and activation energy in OFET devices before and after doping were characterized,and the effect of doping on electron injection and charge transport in OFET devices was explored.（3）On the basis of the above work,a series of p-type semiconductors and n-type semiconductors with high doping concentration were prepared,the changes of their work function and electrical conductivity were measured,and the characterization of thermoelectric devices was carried out,which further confirmed that doping effectively modulate the polarity and electrical properties of PBBT-4T-2F.In addition,an organic PN homojunctio n based on solution processing is constructed for the first time,which provides a good platform for studying organic semiconductor physics and fabricating functional devices such as organic photodiodes.The findings of this thesis provide a paradigm for the use of silicon-like doping techniques in OSCs-based electronic devices.