1T‴ Transition-Metal Dichalcogenides: Strong Bulk Photovoltaic Effect for Enhanced Solar-Power Harvesting

Ferroelectrics is expected to be an alternative to traditional solar cells, because its bulk photovoltaic effect (BPVE) may overcome the Shockley–Queisser limit. Here, we propose that a family of polar materials without centrosymmetry, distorted 1T (1T′′′) transition-metal dichalcogenides, shows a large BPVE in the infrared and visible light due to their moderate band gaps based on density-functional-theory (DFT) calculations. We find that the BPVEs in bulks are much higher than those in monolayers because of the smaller band gaps and more delocalized valence band states. We further show that strain engineering serves as an efficient strategy to enhance the BPVE of 1T′′′-MoS2 bulk. The shift-current responses in the bulks spotlight their potential for applications into solar energy harvesting. This work provides the theoretical evidence of BPVE in 1T′′′ transition-metal dichalcogenides and guidance on the design of novel materials with an enhanced BPVE for green-energy technologies.