Structure, stability and work functions of the low index surfaces of pure indium oxide and Sn-doped indium oxide (ITO) from density functional theory

Indium sesquioxide is a transparent conducting oxide material widely used in photovoltaic and solid-state lighting devices. We report a study of the surface properties of the thermodynamically stable bixbyite phase of In2O3 using density functional theory. The surface energies follow the order γ(100) > γ(110) > γ(111), with the charge neutral (111) termination being the lowest energy cleavage plane. The surface work functions (vertical ionisation potentials) are calculated using a non-local hybrid density functional, and show good agreement with recent experimental measurements. Finally, SnO2 doping of the (111) surface is presented, where the Sn substitutions are more favourable on the surface sites and the excess electrons are delocalised amongst the In2O3 conduction states; the enthalpy of solution is estimated to be 60 kJ mol−1.