Influence of Sodium Concentration on the Optoelectronic Properties of Silicon Clathrate Films

Due to their original optoelectronic properties and cage-like structure, type-II silicon clathrate (Na x Si 136 ) films are investigated as a new silicon-based material for energy applications. In view of the devices and applications, understanding the energy levels of these clathrates is crucial and needs to be investigated as they vary strongly with Na concentration. In this study, we determined the optical bandgap energy, work function, ionization energy, and surface photovoltage for a wide range of compositions ranging from Na 0.1 Si 136 to Na 23 Si 136 . Our findings reveal that the semiconducting properties and potential as solar cell absorbers are dramatically dependent on the Na concentration, with nearly Na-free cages showing the most promise for device applications.