Enhancing Morphological and Optoelectronic Properties of Silicon Clathrate Films through Thermal Press Annealing and SF6 Treatment

Abstract

Although silicon clathrates were discovered about 60 years ago, there has been little research on diverse applications of such materials beyond thermoelectrics. With a direct bandgap of about 1.7 eV and given the advantages of the silicon element such as abundance, nontoxicity and stability, silicon clathrates hold potential for use in photovoltaics and optoelectronics. Additionally, due to their unique cage structure that can store and release sodium atoms with minimal lattice parameter changes, they are promising for battery applications. However, issues like nonhomogeneity, defects, and poor density in clathrate films have hindered such applications. We provide in this work substantial pathways to mitigate such issues with the use of SF₆ etching and thermal press annealing, enabling an improvement of the optoelectronic properties, by a factor of 7 as observed by the surface photovoltage technique. The photovoltage response of above 200 mV at 0.2 sun being above key photovoltaic thin film absorbers such as CIGS and rivaling III–V semiconductors such as GaAs.