Pb-free halide double perovskites: Computational materials design and surface properties

Halide double perovskites have been investigated extensively as lead-free alternatives to lead halide perovskites. Since our theoretical predictions, four crystals have successfully been synthesized: Cs₂BiAgCl₆, Cs₂BiAgBr₆, Cs₂SbAgCl₆, and Cs₂InAgCl₆. These compounds exhibit low carrier effective masses, and Cs₂BiAgBr₆ has a band gap of 1.9 eV, well within the visible range. Hence, these are candidates for opto-electronic applications such as photovoltaics, sensors, and photo-catalysts. In this talk, we will briefly present the computational design principles that lead to the synthesis of these compounds. In addition, we will focus on the structural and electronic properties of the four synthesised compounds and their surfaces. We will show that based on first-principles calculations, double perovskites Cs₂BiAgCl₆ and Cs₂BiAgBr₆ might be promising compounds for photo-catalytic water splitting. For all compounds it is shown that their energy levels, hence their photocatalytic properties, strongly depend on the surface termination. Our computational findings expand the range of potential applications of Pb-free double perovskites.