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

SrTcO 3 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 SrTcO 3 , 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 SrTcO 3 is larger than that of the commonly used substrate SrTiO 3 (STO)/La 0.3 Sr 0.7 Al 0.35 Ta 0.35 O 9 (LSAT)/NdGaO 3 (NGO)/LaAlO 3 (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 SrTcO 3 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 SrTcO 3 is a good candidate for a new solar energy material.