CuInSe₂ quantum dots grown by molecular beam epitaxy on amorphous SiO₂ surfaces

The currently most efficient polycrystalline solar cells are based on the Cu(In,Ga)Se₂ compound as a light absorption layer. However, in view of new concepts of nanostructured solar cells, CuInSe₂ nanostructures are of high interest. In this work, we report CuInSe₂ nanodots grown through a vacuum-compatible co-evaporation growth process on an amorphous surface. The density, mean size, and peak optical emission energy of the nanodots can be controlled by changing the growth temperature. Scanning transmission electron microscopy measurements confirmed the crystallinity of the nanodots as well as chemical composition and structure compatible with tetragonal CuInSe₂. Photoluminescence measurements of CdS-passivated nanodots showed that the nanodots are optoelectronically active with a broad emission extending to energies above the CuInSe₂ bulk bandgap and in agreement with the distribution of sizes. A blue-shift of the luminescence is observed as the average size of the nanodots gets smaller, evidencing quantum confinement in all samples. By using simple quantum confinement calculations, we correlate the photoluminescence peak emission energy with the average size of the nanodots.