Silicon quantum dot/crystalline silicon solar cells

Abstract

Silicon (Si) quantum dot (QD) materials have been proposed for ‘all-silicon’ tandemsolar cells. In this study, solar cells consisting of phosphorus-doped Si QDs in aSiO2 matrix deposited on p-type crystalline Si substrates (c-Si) werefabricated. The Si QDs were formed by alternate deposition ofSiO2 andsilicon-rich SiOx with magnetron co-sputtering, followed by high-temperature annealing. Current tunnellingthrough the QD layer was observed from the solar cells with a dot spacing of 2 nm or less.To get the required current densities through the devices, the dot spacing in theSiO2 matrix had to be 2 nm or less. The open-circuit voltage was found to increase proportionallywith reductions in QD size, which may relate to a bandgap widening effect in Si QDs or animproved heterojunction field allowing a greater split of the Fermi levels in the Si substrate.Successful fabrication of (n-type) Si QD/(p-type) c-Si photovoltaic devices is anencouraging step towards the realization of all-silicon tandem solar cells based on Si QDmaterials.