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 x 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 alpha-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.