Method of fabricating third generation photovoltaic cells based on Si quantum dots using ion implantation

Herein we report the synthesis of silicon quantum dots for novel photovoltaic applications by means of ion implantations process followed by annealing. Nucleation was achieved by impinging Si+ ions into SiO2 thin films grown on a Si (100) substrate and heated at 1100° C and passivating (for photoluminescence (PL) measurements only). The thickness, stoichiometry and depth-profiles versus annealing of all samples were determined by both Rutherford backscattering spectroscopy (RBS) and ellipsometry techniques.We have shown that both implanted Si atoms and native Si atoms (from the SiO2 matrix) contribute to Si nucleation. Transmission electron microscopy (TEM) shows areas of silicon quantum dots (Si-QDs) with sizes varying from 2 to 4 nm, which is less than the Bohr radius of bulk crystalline Si (~ 5 nm). Optical and electrical properties have been investigated by PL and I-V measurements. Passivated silicon nanocrystals (Si-nc) embedded in SiO2 exhibit PL increasing with fluence. According to the statistical model for luminescence emission, we derive a typical radius of 3 nm for luminescent QDs around Lambda = 800 nm. Based in these investigations, p-type Si-QDs / n-type c-Si junctions were fabricated and electrically characterised in the dark and also under an AM1.5G terrestrial solar spectrum for non-implanted, as-implanted and implanted-annealed samples for different fluences. The electrical curves of the structure under illumination demonstrate the photovoltaic behaviour of the Si-QDs. Despite the weakest light conversion of these devices, this result remains very promising and offering unprecedented vast improvements to third generation solar cells.