Janus Bi2XYZ monolayers for light harvesting and energy conversion from first-principles calculations

Abstract

Abstract In this work, two-dimensional (2D) Janus Bi2XYZ (X≠Y≠Z, X/Y/Z = S, Se, Te) are predicted to be stable by means of the first-principles calculations. It is of interest that inversion asymmetry induced out-of-plane electric field causes the indirect–direct band gap crossover, band gaps for Bi2SeSTe, Bi2SSeTe and Bi2STeSe are approximately 0.7 eV (at HSE + SOC level of theory). For these Janus structures, carrier mobility reaches up to 3282.05 cm2 V−1 s−1, highly desirable for electronics, light harvesting and energy conversion. Janus Bi2XYZ show strong light–matter interactions, with the optical absorption covering almost the entire incident solar spectrum, thus ensuring efficient utilization of solar energy. For Janus Bi2XYZ, the piezoelectric coefficient d 11 can be as high as 15.01 pm/V due to the inversion symmetry breaking, higher than most of the reported Janus structures. And there is a linear relationship between the piezoelectric coefficient d 11 and the potential energy difference Δ φ between two outmost atomic layers. Our work thus demonstrates that 2D Janus Bi2XYZ hold great promise in applications in such as electronics, light harvesting and energy conversion.