Wurtzite zinc-based oxynitrides as promising photovoltaic absorbers: epitaxy, band-structure engineering and heterostructures

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This project aims to overcome the fundamental problems of thin film solar cells, such as low cell conversion efficiency as well as technical barriers for the use of non-toxic materials. For this purpose, a new class of unconventional semiconductors with wurtzite structure will be developed by alloying ZnO with III-nitrides (AlN, GaN, InN). Bandgap engineering of such Zn-based oxynitride thin films is achievable by modulating the valence and/or conduction band edges. The substitution of both anion (N on O-site) and cation (Al, Ga and In on Zn-site) allows controllable band structures while ensuring crystallinity. As proof of concept we could reduce the bandgap of ZnO-GaN much below the values of the single compounds. The bandgap would be thereby modulated into the visible light or near-infrared regions (near 1.3 eV) for effective solar-light harvesting. The anticipated goal is tackling the critical problems of Zn-based materials in epitaxial growth and band-structure engineering for photovoltaic application.