The Effect Of The Dielectric Surface Energy On Electrical Properties Of Organic Transistors And Its Mechanism

Organic field-effect transistors（OFETs）are the active devices that regulate the current between the source electrode and drain electrode through gate voltage and dielectric layer.Different from the inorganic devices,the organic devices can keep electrical performance under different deformation states due to their advantages of lightweight and flexibility.OFETs have significant advantages in the application,such as the bionic electronic skin,implanted biochips,flexible display and a new generation of elastic and flexible wear smart products.The mobility is one of the most important parameters to evaluate the organic semiconductor materials and device performance,which determine the switching speed,driving ability and device size.The higher mobility renders the devices possess wider application fields.There is an intensive dependence on the properties of the dielectric layer for the charge transmission and electrical performance of device,because the conductive channel is located at only a few molecular layers near the organic semiconductor/dielectric interface.Hence the dielectric modification has become one of the main methods to improve the mobility.For thin-film transistors,however,the interface properties of the dielectric layer not only affect the carrier transmission,but also directly affect the growth of thin films,which is not conducive to study the intrinsic properties in organic devices.There are many conflicts among the reported results from different groups.In our experiments,organic single-crystal OFETs are fabricated by mechanical transferring,which can avoid the influence of the dielectric properties on the growth of crystal and obtain a new intrinsic regular in OFETs.The main contents are as follows:1.The ultrathin dinaphtho[3,4-d:3′,4′-d′]benzo[1,2-b:4,5-b′]dithiophene（Ph5T2）single crystals are obtained by a physical vapor transport technique and Ph5T2 single-crystal OFETs have been fabricated on eight dielectrics with different surface energy by the mechanical transfer method of"gold film stamping",to study the dielectric properties on the influence of its mobility.The results show that the surface polarity,surface roughness and total surface energy of the dielectric layer are not the key factors to determine the field-effect mobility.Only the closely matching both polar and dispersive components of the surface energy of dielectric with those of the semiconductor are favorable for the OFETs with high device mobility.Such as Ph5T2 single-crystal OFETs with the highest mobility 2.15cm²V^-1s^-1 are obtained on the BPPh-modified Si O₂ dielectric that matches with the Ph5T2surface energy components.The theoretical analysis show that matching surface energy can reduce the interfacial tension of semiconductor/dielectric layer,and then reduce the shallow defect density in conductive channel to obtained the higher mobility.2.To verify the generality of the findings that surface energy components matching can improve mobility,we choose the traditional pentacene and zinc phthalocyanine（ZnPc）single crystals,and fabricate the single-crystal OFETs on three dielectrics（Si O₂,p-6P-modified Si O₂ and OTS-modified Si O₂）with different surface energy.The results show that the maximum mobility was 5.29 cm²V^-1s^-1 and 0.60 cm²V^-1s^-1 on the dielectric layer（p-6P-modified Si O₂ and OTS-modified Si O₂）that are matched with the semiconductor（pentacene and ZnPc）surface energy components,respectively.Based on the pentacene and ZnPc single-crystal OFETs,it verifies successfully the generality of the findings that surface energy components matching can improve the mobility.The conclusion is compatible with the most widely accepted theory on international reports,and can explain most of the existing contradictions between theory and experiment.It is an important breakthrough in the field of basic theory in OFETs,which will greatly simplify the dielectric selection process in device optimization and the intrinsic performance study process of new material.3.Based on the findings of the surface matching to improve the mobility,we have obtained the highest mobility among the reported values based on dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene（DNTT）single crystal OFETs.According to the tested surface energy of DNTT semiconductor material,HMDS-modified Si O₂ dielectric layer which matched with DNTT surface energy is selected,and DNTT single-crystal OFETs are fabricated.The experimental results show that the maximum mobility of DNTT single-crystal OFETs is as high as 13.02 cm²V^-1s^-1 on HMDS-modified Si O₂,which reflects the material intrinsic properties and the correctness of our findings.