First-principles prediction of a rising star of solar energy material: SrTcO_3

SrTcO3 as a new star of solar energy material is investigated in terms of its band gap evolution with biaxial strain from first-principles calculations. Compared to the theoretical equilibrium lattice constant a(b) of bulk SrTcO3, a set of lattice constants with a deviation of -8.75% to +3.35% are considered to include the strain effect. Since the in-plane lattice constant of SrTcO3 is larger than that of the commonly used substrate SrTiO3(STO)/La0.3Sr0.7Al0.35Ta0.35O9 (LSAT)/NdGaO3(NGO)/LaAlO3(LAO), we mainly focus on the modulation of compressive strain. It is found that the band gap decreases with increasing compressive/tensile strain. When the compressive strain reaches 8.75%, the band gap drops to zero and an insulator-metal phase transition appears. Particularly, upon a compressive strain of 1.3%/2.2%/2.4%/4.1%, which can be realized by growing SrTcO3 on substrate STO/LSAT/NGO/LAO, the band gap becomes 1.56/1.47/1.43/1.12 eV, which falls in the range for efficient solar cell materials. Our work suggests that SrTcO3 is a good candidate for a new solar energy material.