Tailoring of the Structural and Optoelectronic Properties of Zinc-Tin-Oxide Thin Films via Oxygenation Process for Solar Cell Application

Abstract

In this study, the impact of compositional variation in high resistance transparent (HRT) metal oxide ZTO films of thickness around 100nm has been investigated. The atomic composition in the films has been tailored by the change of RF power and sub-sequent thermal oxygenation in mixed nitrogen and oxygen atmosphere. A phase transition from ZnSnO3 to ZnSnO4 was observed in the X-ray diffraction spectra, indicating the possible oxygen incorporation into the films during the thermal annealing process. Uniform microstructures with compact interconnected grains of around 6-7 nm were found in SEM images while no significant changes been observed upon oxygenation. Besides, the significant alteration of electronic properties was noticed as an effect of compositional variation via oxygenation. All the films showed above 85% of optical transmittance in the visible light spectrum. The optimum optoelectronic properties for RF power has been determined as of 50W (ZnO) and 10W (SnO2) via thermal oxygenation at 400°C where the ratio O/(Zn+Sn) become around 1.6. The significant effect of oxygenation has been realized via primarily fabricated solar cells where the cell with ZnSnO4HRT shows higher efficiency than the ZnSnO3.