Band modification of tin nitride thin films for green energy generation

Abstract

The application of photovoltaic technology is limited due to scarcity and toxicity of the efficient materials used for the energy conversion process. Nitride–based binaries can resolve these challenges by their abundance and non–toxicity as well as flexible structure–property correlations emerging from the moderate electronegativity of the nitrogen atom. In this work, thin films of earth abundant tin nitride (Sn3N4) with optimized bandgap and high absorption coefficient were fabricated by reactive radio–frequency magnetron sputtering. The control over the multiple fabrication parameters concurrently stimulated the thin films to grow with (222) orientation instead of (311) as well as with increased defect density by taking the benefit of nitrogen as sputtering and reactive gas. The gradual reduction in bandgap along with increasing (222) orientation converged the light and the heavy conduction bands and hence increased the valley degeneracy, density of states and absorption coefficient. These features of band evolution were confirmed by integrating the optical analyses with thermoelectric parameters such as conductivity and Seebeck coefficient. The engineered band structure transformed the Sn3N4thin film as a photovoltaic conversion material by narrowing the bandgap from 2.06 eV to an optimized value of 1.51 eV with an absorption coefficient of the order of 104/cm. This study explored the potential of transfiguring earth abundant nitrides as conversion materials for renewable energy harvesting. The experimental strategy used to engineer the band structure can be exploited to optimize the carrier properties of thin films for various applications.