Oxygen concentration as a combinatorial parameter: The effect of continuous oxygen vacancy variation on SnO₂ layer conductivity

Combinatorial materials science is a powerful approach to discover new materials, especially by using the continuous compositional spread (CCS) method, which forms spatially varying stoichiometry across a sample. Though the chemical composition of the candidate materials is typically the primary parameter studied, in the case of metal oxides CCS the oxygen concentration is usually either neglected or studied in a discrete and non-combinatorial manner. The present work reports the use of oxygen concentration as a combinatorial parameter that varies continuously across a sample, using a pulsed laser deposited (PLD) SnO₂ film as a model system. As the oxygen concentration decreases, the SnO₂ crystal lattice expands, the number of defects is increased, and the electrical conductivity rises exponentially. A relatively low electrical resistivity of 8.16∙10⁻⁴ Ω cm is achieved. The sample also showed superior infrared transparency, 67% at 2000 nm, compared to commercial F:SnO₂ (FTO) which is only 12% transparent at this wavelength. The improved transparency and conductivity were achieved within a single experiment, without any additional optimization steps, and with further improvement may allow reconsideration of SnO₂ as a transparent conductive oxide. Our findings serve as a demonstration for the importance of oxygen concentration as a combinatorial parameter.