Study On The Effect Of Electrode Modification On The Performance Of OFETs

Organic field effect transistors（OFETs）have been widely studied for its flexibility,low-cost,simple process,and good biocompatibility,and have been applied in the fields of radio frequency identification（RFID）,flexible display drivers,and electronic paper.However,the problem of the contact between electrodes and organic semiconductors has always been a key element limiting the performance of devices.At present,the main reasons for the contact problem between electrodes and organic semiconductors are as follows:the work function of electrodes not match the HOMO（LUMO）level of the organic materials;dipole is generated when the electrode is in contact with an organic semiconductor.;in addition,when the metal electrodes prepared by evaporation,sputtering,the high-energy metal particles will damage the surface of the organic materials.Therefore,contact problems limit the carrier injection and have a serious impact on the performance of OFETs devices.In addition,high work function electrode materials（Au,Pt,etc.）are widely used as electrode materials for p-type OFETs.These materials have a high work function（～5.0 e V）and can effectively match with the HOMO level（～5.0 e V）of organic semiconductor materials.However,the precious metal properties of materials such as Au and Pt limit their use in the commercial field of low-cost and large-area preparation.Therefore,extensive research has been obtained by electrode modification to improve the work function of the surface of the low work function electrode materials and to improve the injection of carriers into the organic semiconductor materials.In this paper,Cu is used as the electrode material due to its large-area and low-cost preparation,heavy-doped high-resistivity（1-5Ω·cm）n-type silicon as dielectric layer and substrate,and pentacene is used as organic semiconductor material.The effect of electrode modification on the performance of OFETs with different structures is studied.The first part of this experiment,the bottom gate top contact OFETs were prepared by modifying Cu electrode with high work function material-V₂O₅.The results show that when the thickness of V₂O₅ is0.5nm,the device performance is the highest.because the addition of V₂O₅ reduces the injection complex)is formed when V₂O₅ is in contact with pentacene.When the gate voltage is applied,the dissociation of the CT mixed layer will inject holes into the pentacene,improving carrier injection efficiency.Therefore,the addition of V₂O₅ relieves contact problems and improves carrier injection efficiency,thereby improving device performance.In the second part of this experiment,the bottom gate bottom contact OFETs were fabricated by modifying the electrodes with a highly polarized PFBT SAM layer.In this part of the study,it was found that（1）the bottom-gate bottom contact OFETs can improve the growth of the pentacene film after proper annealing（120℃,5min）,thereby improving the carrier transport efficiency.（2）Excessive thick electrodes may result in poor growth of the pentacene film nearby the electrode,thereby affecting device performance.Therefore,bottom gate bottom contact OFETs are not suitable for thick electrodes.（3）After PFBT SAM modification,the device performance is improved,mainly because PFBT forms a SAM layer with a considerable dipole moment on the Cu surface,and the existence of the dipole layer can change the work function of the surface of the Cu electrode.In addition,the template properties of the SAM layer can induce nucleation of the pentacene film.In summary,the modification of the Cu electrode by the PFBT SAM layer can improve the contact problem and improve the device performance.In this paper,the regulation of charge transport by electrode modification improves the performance of OFETs,indicating the importance of electrode modification in controlling interface carrier transport and the practicability of this approach.