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 × 104 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 103 cm2 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.