Sn9C15 monolayer with desirable bandgap, high carrier mobilities, and broadband light absorption for photovoltaic devices

Two-dimensional carbon-based materials show considerable promise for applications in a wide range of fields, including aerospace, energy storage, and catalysis, due to their great advantages of abundant carbon resources, relatively low-cost, non-toxicity, and excellent physical and chemical properties. However, their applications in photovoltaics remain limited. Here, we first theoretically predict a stable Sn9C15 monolayer (space group P321). The Sn9C15 monolayer exhibits numerous advantages, which make it an ideal candidate for photovoltaic applications: (1) The Sn9C15 monolayer is a direct bandgap semiconductor with a bandgap of 1.70 eV, which is closer to the optimal bandgap of 1.50 eV for photovoltaic devices; (2) the Sn9C15 monolayer exhibits electron mobilities in excess of 2 × 103 cm2 V-1 s-1; (3) the Sn9C15 monolayer shows a direct bandgap of 1.50 eV under a 3% compressive biaxial strain; (4) the Sn9C15 monolayer shows a benign light absorption in the whole visible region (380-780 nm); (5) the Sn9C15 monolayer possesses an optical bandgap of 0.97 eV and an exciton binding energy of 1.63 eV; and (6) the Sn9C15/TMD heterostructures are predicted to have a power conversion efficiency of 9%-23%. In terms of its formation energy, we expect that the Sn9C15 monolayer will be fabricated similarly to the synthesized Si9C15 monolayer. Importantly, the target bandgap of the Sn9C15 monolayer is achieved by the synergistic mechanism of the crystal lattice spacing and the atomic contribution of band edges (referred to as lattice-band edge synergistic mechanism). We anticipate that this synergistic mechanism will facilitate the design of a great number of new materials with targeted bandgaps.