Computational screening for effective Ge1−xSix nanowire photocatalyst

Abstract

We perform a comprehensive mapping of GeSi nanowire (NW) electronic band characteristics versus the alloy composition and the diameter (up to 3 nm) using hybrid density functional theory (DFT) calculations, the cluster expansion method and Monte Carlo simulations. We reveal that stable alloy GeSi NW configurations across compositions tend to exhibit asymmetric core–shell structures, which enhance spatial separation of the band edges, making them more effective for electron–hole charge separation as compared to conventional symmetric core–shell structures. More importantly, from the composition-size map of the NW band edges, we show that GeSi NWs with diameters below 3 nm are thermodynamically capable of photocatalysing water-splitting reactions (alkaline conditions) and CO₂ reduction. In particular, NWs with diameters of 2 and 3 nm possess desirable properties for efficient photo-conversion; their bandgaps (1.4 to 2.0 eV) match well with the solar spectrum.