Silicon is an important electronic material in technological fields, but it is a poor optoelectronic material with a direct optical gap larger than 3 eV. In the last few decades, researchers have studied the structural and electronic properties of silicon in order to improve its optical absorption in the visible light range using analyses of metastable silicon phases, silicon-based alloys, and silicon-based superlattices. We present new first-principles calculations that hydrogenated bilayer silicene—${\mathrm{SiH}}_x$—is a promising silicon-based optoelectronic material capable of revolutionizing how solar power is collected.

We theoretically predict that chemically functionalized hydrogenated bilayer silicene has great potential as a new kind of silicon-based optoelectronic material other than diamond silicon. Hydrogenation can significantly improve the optoelectronic properties of bilayer silicene and yield a widely tunable band gap, which can be realized even at zero temperature. At low hydrogen concentrations, four single- and double-sided hydrogenated bilayer silicene ground-state structures have been identified to have dipole-allowed direct (or quasidirect) band gaps between 1 and 1.5 eV, suitable for solar applications. Our optical calculations confirm that these four hydrogenated bilayer silicene ground states do indeed have much stronger absorbance than diamond silicon, which is currently used in over 90% of solar cells. Surprisingly, at high hydrogen concentrations, we also discover three well-ordered double-sided hydrogenated bilayer silicene structures that have direct (or quasidirect) band gaps within the color range of red, green, and blue. These structures can be used to build a silicon-based, white-light-emitting diode, which has great potential for solid-state lighting.

Hydrogenated bilayer silicene affords the opportunity to create efficient thin-film solar absorbers and silicon-based, white-light-emitting diodes, paving the way for new “green” energy applications.