New Lattices For Silicon Solar Cells

Materials scientists backed by computer simulations have identified several silicon lattice arrangements that are predicted to be more efficient at converting sunlight to electricity than are the cubic diamond structures typically employed in crystalline silicon solar cells (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja5035792). Some of the most efficient solar modules on the market rely on silicon’s diamondlike allotrope. But these crystals harbor an inherent inefficiency: an indirect band gap. Incident light shining on the solar cells needs an assist from lattice vibrations, or phonons, to excite charge carriers to the material’s conduction band and generate an electric current. Julong He of China’s Yanshan University and his coworkers identified six different silicon geometric crystal arrangements (three shown) with direct or quasidirect band gaps that should produce a photocurrent without phonons. In addition, the team’s simulations revealed that the crystals should be stable at room temperature, and five of them should survive beyond 700 °C, which the researchers believe is further cause for optimism. Actually fabricating these structures is the next challenge, but scientists have already developed techniques for packaging group 14 elements into various crystalline configurations, He says.