The electronic structure of the sputtered indium–tin oxide and a thin conjugated oligomer film interface

The interface formation between indium–tin oxide (ITO) and a conjugated oligomer (Ooct-OPV5, [(2,5-Bis(4-styryl) styryl)1,4-dioctyloxybenzene]), was studied by X-ray and ultraviolet photoelectron spectroscopies (XPS, UPS). The oligomer was stepwise deposited on a sputter-cleaned ITO film under ultrahigh vacuum conditions. The shape and position of the ITO related XPS peaks did not change during the deposition procedure. At the first stages of the Ooct-OPV5/ITO interface formation and up to the completion of ∼1 oligomer monolayer, the oligomer related XPS C1s peak exhibited a high BE component and a ∼0.25 eV upward BE shift, which were attributed to the interfacial interaction. The total work function change upon deposition of the oligomer on ITO was ∼0.20 eV and corresponded to the formation of a dipole layer at the interface. The interfacial band diagram was deduced from the combination of XPS and UPS results.