Study On Electrical Contact Doping For Polymer Transistors

In the past 30 years,organic electronic has received widespread attention for its excellent flexibility and mechanical properties and will play an important role in flexible electronics in the future.Especially in recent decade,organic electronics have been widely applied to many fields like organic field-effect transistor（OFET）,organic photovoltaic,radio frequency identification tags（RFID）and digital logic circuit.OFET is a voltage-controlled device which uses organic semiconductor as active layer and has the broadest development prospect among all organic devices.Nevertheless,compared with traditional inorganic-semiconductor-based devices,OFET has serious issue on charge injection,especially in those with coplanar architecture.This thesis is dedicated to improving the contact performance between metal and semiconductor,and therefore enhanceing charge injection,and solving the problem of the coplanar polymer transistors that do not work without doping.To improve the charge injection problem caused by contact,in general,the metal with suitable work function is often chosen as the electrode.But even gold with a large work function does not match well with the energy level of p-type polymer semiconductors that typically have wide band gap.Therefore,it is necessary to consider another method,that is,doping.The method adopted in this thesis is contact doping,and the process is to deposite Mo O₃ with different thickness as doping layer at the contact interface between metal electrode and organic semiconductor layer（DPPT-TT）by thermal evaporation.Through a series of experiments,it was found that the coplanar polymer transistor started to work after contact doping,and reached the best performance when the thickness of the doping layer was 3 nm.This thesis analyzed the mechanism of contact doping according to the experimental results.Contact doping can reduce the Schottky barrier at the contact between metal and organic semiconductor,thinning the depletion layer so that the charge carriers can be injected through high-efficiency tunneling.In addition,doping passivates the traps in the contact area.As a result,the overall charge transport is greatly improved.The finding of this thesis provides the possibility of applying OFET to many fields in the future.