Computational Discovery of Novel Chalcogenide Perovskites YbMX₃ (M = Zr, Hf; X = S, Se) for Optoelectronics

Chalcogenide perovskites have shown great potential for photovoltaic applications. Most researchers have begun to pay close attention to the crystal synthesis, phase stability, and optoelectronic properties of chalcogenide perovskites AMX₃ (A = Ca, Sr, Ba; M = Ti, Zr, Hf, Sn; X = S, Se). At present, the A-site metal cations are mainly limited to alkaline earth metal cations in the literature. The replacement of the alkaline earth metal cations by Yb²⁺ is proposed as an alternative for chalcogenide perovskites. In this study, the phase stability, and mechanical, electronic, optical, and photovoltaic properties of novel chalcogenides YbMX₃ (M = Zr, Hf; X = S, Se) are theoretically evaluated in detail for the first time. It is mentioned that YbZrS₃ and YbHfS₃ are marginally thermodynamically stable while YbZrSe₃ and YbHfSe₃ exhibit superior phase stability against decomposition. Good mechanical and dynamical stability of these chalcogenide perovskites are verified, and they are all ductile materials. The accurate electronic structure calculations suggest that the predicted direct bandgap of YbMSe₃ (M = Zr, Hf) is within 1.3-1.7 eV. Additionally, the small effective mass and low exciton binding energy of YbMSe₃ (M = Zr, Hf) are favorable for their photovoltaic applications. However, YbZrS₃ and YbHfS₃ show larger direct band gaps with a change from 1.92 to 2.27 eV. The optical and photovoltaic properties of these compounds are thoroughly studied. In accordance with their band gaps, YbZrSe₃ and YbHfSe₃ are discovered to exhibit high visible-light absorption coefficients. The maximum conversion efficiency analysis shows that YbMSe₃ (M = Zr, Hf) can achieve an excellent efficiency, especially for YbZrSe₃, whose efficiency can reach ~32% in a film thickness of 1 μm. Overall, our study uncovers that YbZrSe₃ is an ideal stable photovoltaic material with a high efficiency comparable to those of lead-based halide perovskites.