Method for fabricating third generation photovoltaic cells based on Si quantum dots using ion implantation into SiO2

Abstract

In this paper, we report on the synthesis of silicon quantum dots for photovoltaic applications by means of ion implantation followed by annealing. Nucleation was achieved by implanting Si+ ions into SiO2 thin films, previously thermally grown on a Si(100) substrate, and annealing to 1100 °C. Passivation was used for photoluminescence (PL) measurements. The thickness of the oxide layer, the stoichiometry of the implanted layer, and the depth profiles of the implanted ions were determined for all samples by both Rutherford backscattering spectroscopy (RBS) and ellipsometry techniques. Characterization by transmission electron microscopy (TEM) indicates that the diameter of the silicon quantum dots (Si-QDs) varies 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. When passivated silicon nanocrystals (Si-nc) embedded into SiO2 are excited using a 450 nm diode laser, they exhibit a strong PL emission in the range of 650-1000 nm. Based on these investigations, p-type Si-QDs/n-type c-Si junctions were fabricated and electrically characterized in the dark as well as under an AM1.5G terrestrial solar spectrum for nonimplanted, as-implanted, and implanted-annealed samples for different implantation fluences. The electrical curves of the structures under illumination demonstrate the photovoltaic behavior of the Si-QDs. Despite the weak light conversion of these devices, these results remain very promising and offer potentially unprecedented, vast improvements to third generation solar cells.