The silicon bandgap is controlled by quantum confinement of carriers in artificial semiconductor quantum dots, which behave like individual atoms. If they are close enough to interact, atomic-like energy levels broaden out into bands analogous to the conduction and valence bands of a bulk semiconductor. This gives rise to an amorphous-type semiconductor material with electrical and optical properties that may be tuned by adjusting the dot size, density and host material.

In a recent paper about quantum dot/crystalline silicon solar cells published in Nanotechnology it was found that silicon quantum dots surrounded by the 2 nm thick insulating oxide matrix with additional phosphorus doping play an important role in carrier transport. An oxide film on crystalline silicon does not show a device property, unless an ultra-thin oxide layer (<3 nm) in a metal–insulator semiconductor solar cell is used. The photo-generated carriers in the silicon quantum dot/silicon device are transported through silicon quantum dots or trap-assisted tunnelling via defects in the SiO2 matrix until carriers reach the device electrodes.

Successful fabrication of the silicon quantum dot/silicon photovoltaic devices is an encouraging step towards the realization of all-silicon tandem solar cells based on silicon quantum dot materials.