Chemical functionalization induced photocatalytic performance for water splitting of silicene: A first-principles investigation

To expand the application of silicene in the field of optoelectronics, here, the structural and mechanical stability, electronic, optical and photocatalytic properties of silicene Janus-functionalized by hydrogen and halogen atoms are investigated via density functional theory (DFT) calculations. The stability of Janus-functionalized silicene monolayers is confirmed by ab initio molecular dynamics (AIMD) simulation and the cohesive energy. Mean-while, the linear elastic constants also confirm the mechanical stability of Janus-functionalized silicene mono-layers. After chemical functionalization, the resultant semiconductors exhibit a direct band gap in the range of 1.87-2.62 eV, as calculated by the HSE06 method. The work function for Janus-functionalized silicene mono-layers show a decreasing trend as the atomic number of the halogen is increased. Besides, the results show that the optical absorption of silicene can be effectively improved by the selective functionalization of different halogen atoms on half-hydrogenated silicene. Particularly, the enhanced optical absorption coefficient of visible light in the range from 2.8 x 105 to 4.3 x 105 cm-1 can be obtained. Furthermore, the suitable band edge positions of HSiF, HSiCl and HSiBr fully meet the requirements of redox potential, which suggests these cases could be efficient water splitting materials.