First principles study for band engineering of KNbO₃ with 3d transition metal substitution

First principles calculations in the framework of density functional theory (DFT) were performed to tune the electronic structures of wide gap KNbO₃ through 3d transition metal substitution, using PBE and HSE06 functionals for the exchange correlation potentials. While PBE functionals are suitable for structural and energetic properties, HSE06 is more reliable for band structure calculations. Impurity bands owing to V, Mn, or Fe are present in the forbidden gap, leading to effective reduction of optical gaps via multiple wavelength absorption. It is discovered that Ti and Cr doped systems are suitable for n type transparent conducting oxide (TCO), the Ni doped system for highly desirable p type TCO, and the Cu doped system is an excellent candidate for p type optical absorber layers. This work provides a systematic and overall perspective on the effects and associated mechanisms of transition metal doping or alloying, thus helping exploitation of perovskite oxides as potential key materials for photovoltaic and transparent photonic applications.