Modification of Indium Tin Oxide Surface with HCl for Source/Drain Electrodes in Organic Thin Film Transistors

In recent years, exciting advances have been achieved in pursuing organic thin film transistors (OTFTs) with high mobility. Whereas, the economical infeasibility of Au source/drain (S/D) electrodes that are widely used in OTFTs hinders the further development of OTFTs in industry. In this study, the modified indium tin oxide (ITO) as S/D electrodes is adopted. The ITO is modified by HCl aqueous solutions, its surface work function is improved from 4.8 to 5.5 eV. By first-principle calculations and experiments, the charge analysis shows that the Cl atom traps 0.475 electrons, which indicates that In-Cl dipoles are responsible for the increase of the surface work function, besides the HCl modification leads to In+-Cl- bonds instead of In3+-Cl- bonds on the ITO surface compared with the reported InCl3 modification. More encouragingly, In+-Cl- surface is found to have higher Cl density, higher work function and higher conductivity. TIPS-pentacene, with suitable HOMO level of 5.2 eV, is adopted as organic semiconductor, and the bar-coating process is optimized to realize oriented films. OTFTs with maximum field-effect mobility of 0.77 cm(2) V-1 s(-1) are achieved. The ITO electrodes modified by HCl can be promising in the industry.