Surface oxidation activates indium tin oxide for hole injection

Oxygen plasma treatment of indium tin oxide (ITO) results in a change in work function and electron affinity by similar to 0.5 eV. This change correlates with the measured increase in injected current in simple hole-only organic devices with O-plasma treated ITO electrodes. Neither addition nor removal of surface hydroxyl functionality accounts for the observed work function and electron affinity changes. X-ray and ultraviolet photoelectron spectroscopies show a new type of oxygen species is formed. Oxidation of surface Sn-OH to surface Sn-O-. units is proposed to account for the observed changes in O-plasma treated ITO; this proposal can explain a wide variety of previously described ITO surface activation results. (C) 2000 American Institute of Physics. [S0021-8979(00)02501-9].