Two-dimensional Janus monolayers Al2XYZ (X/Y/Z = S, Se, Te, X ≠ Y ≠ Z): first-principles insight into the photocatalytic and highly adjustable piezoelectric properties†
Abstract
Janus materials possess some unique properties that are different from those of a symmetrical structure, which provides them with broad application prospects. In this work, we investigated the photocatalytic and piezoelectric properties of Janus materials Al2XYZ (X/Y/Z = S, Se, Te, X ≠ Y ≠ Z) by first-principles calculations. The results show that Janus monolayers Al2XYZ, with energy, mechanical, thermal, and dynamical stability, have suitable band-edge positions, broad absorption of sunlight (infrared–ultraviolet), high solar-to-hydrogen (STH) efficiency (up to 23.81%) and high carrier transfer in the x-direction (1 × 104 cm2 V−1 s−1). In addition, the photocatalytic water decomposition reaction of the Al2SeTeS monolayer can be carried out spontaneously under an applied potential. The Young's modulus and Poisson's ratio indicated that the Al2XYZ monolayers possess extraordinary flexibility. The in-plane d11 and the out-of-plane piezoelectric coefficient d31 are up to 41.28 pm V−1 and 0.32 pm V−1. Notably, the in-plane piezoelectric coefficient d11 and the out-of-plane d31 are highly adjustable by applying strain/stacking. For Al2SeTeS, they increased by approximately one order of magnitude (d11: from 41.28 pm V−1 to 405.63 pm V−1, d31: from 0.07 pm V−1 to 0.44 pm V−1). These outstanding properties allow Al2XYZ monolayers to be widely used in photocatalysis, flexible nanodevices and piezoelectric sensors.