Surface oxidation activates indium tin oxide for hole injection

Oxygen plasma treatment of indium tin oxide (ITO) results in a change in wo rk function and electron affinity by similar to 0.5 eV. This change correla tes with the measured increase in injected current in simple "hole-only" or ganic devices with O-plasma treated ITO electrodes. Neither addition nor re moval of surface hydroxyl functionality accounts for the observed work func tion and electron affinity changes. X-ray and ultraviolet photoelectron spe ctroscopies show a new type of oxygen species is formed. Oxidation of surfa ce Sn-OH to surface Sn-O-. units is proposed to account for the observed ch anges in O-plasma treated ITO; this proposal can explain a wide variety of previously described ITO surface activation results. (C) 2000 American Inst itute of Physics. [S0021-8979(00)02501-9].