Hexagonal Si polytypes are promising photovoltaic materials, as they have enhanced absorption efficiency of visible light, with a band structure that has been predicted to shift with strain and pressure [1,2]. Until now, synthesis of recoverable hexagonal Si has remained elusive, preventing its industrial application. We recently established the first pure synthesis of hexagonal Si in its bullk form, which is stabilized into the Si-4H structure through high-pressure synthesis [3].

Initial characterization of the pure Si-4H samples has revealed a complex multi-scale structure that adds complexity to their applications to the solar industry. High densities of stacking faults create flake-like crystallites, with unique structures that transform the local order into a powder-like structure over micrometer length-scales. This talk will discuss these recent characterization studies and how they enhance our understanding of hexagonal silicon’s abilities in photovoltaics.

[1] Rödl, C. et al., Physical Review B 92, 045207 (2015).

[2] Karazhanov, S. Z et al.,  Journal of Applied Physics 104, 024501 (2008).

[3] Pandolfi, S. et al., Nano Letters 18, 5989–5995 (2018).