Superior heterojunction properties of solution processed copper-zinc-tin-sulphide quantum dots on Si.

CZTS nanocrystals have been synthesized via a new facile and environmentally friendly route using olive oil at a relatively low temperature. Nanocrystals synthesized using olive oil have a smaller average size in comparison to those synthesized with a conventional solvent-like ethylenediamine. Nanocrystals with an average diameter of 40, 20 and 6 nm have been extracted from the olive oil at different centrifugation speeds of 500, 1000 and 2000 rpm, respectively. The photovoltaic characteristics of p-CZTS/n-Si heterojunctions fabricated using the synthesized colloidal quaternary nanocrystals are demonstrated. The device fabricated with smallest sized CZTS nanocrystals, having an average diameter of ∼6 nm, exhibits an enhancement in power conversion efficiency of 61% in comparison to that of the device fabricated with the nanocrystals of 40 nm in diameter. A lower reflectance and higher minority carrier life time along with a larger surface-to-volume ratio resulted in an enhanced power conversion efficiency for smaller sized CZTS nanocrystals.