Abstract
We propose a two-dimensional material, delta-CS, and show that it is a direct-band-gap semiconductor with strong absorption of solar radiation. Power conversion efficiencies of 7.0% to 20.1% are predicted for solar cells with delta-CS as a donor and a transition metal dichalcogenide as an acceptor. delta-CS also excels in terms of having an exceptionally large negative in-plane Poisson's ratio. Its ferroelasticity with moderate switching barrier is promising for applications in shape memory devices.