Highly efficient photocatalytic water splitting and enhanced piezoelectric properties of 2D Janus group-III chalcogenides

Recently, Janus two-dimensional (2D) materials have received considerable interest due to their intrinsic vertical dipole, and hence they have great potential in photocatalytic and piezoelectric applications. Here, a new series of Janus 2D structures MM′XX′ (M, M′ = Ga, In; X, X′ = S, Se, Te) are investigated by means of first-principles calculations. It is found that 2D Janus MM′XX′ exhibit high dynamical stability and have band gaps in the range of 0.89-2.03 eV. Most outstandingly, these MM′XX′ monolayers exhibit appropriate band edge positions, strong light absorption (1 × 10 4 cm −1 ) in the visible light region, high energy conversion efficiencies (up to 18.51%), effective spatial separation and fast transfer of carriers (at least 10 3 cm 2 V −1 s −1 ), which make them promising candidates for photocatalytic water splitting (except InGaSTe which has a small band gap of 0.89 eV). What is more, the in-plane piezoelectric coefficients of these MM′XX′ monolayers (2.62-6.21 pm V −1 ) are comparable to those of the common bulk materials such as α-quartz (2.3 pm V −1 ), wurtzite GaN (3.1 pm V −1 ) and AlN (5.1 pm V −1 ), and the out-of-plane piezoelectric coefficients (0.28-0.41 pm V −1 ) are higher than those of the Janus MXY (M = Mo, W; X, Y = S, Se, Te) monolayers (0.007-0.030 pm V −1 ). Our findings reveal the potential applications of these monolayers as efficient photocatalysts and piezoelectric materials. A series of 2D Janus group-III chalcogenides have been predicted as promising candidates for photocatalytic water splitting and piezoelectric devices.