Synthesis and properties of Si nanocrystals for photovoltaic applications

Thin films of the Si:O alloy have been systematically characterized in the structural, optical absorption and electrical transport behaviour, by varying the Si content. Magnetron sputtering or plasma enhanced chemical vapour deposition have been used to deposit a single layer, or multilayer structures of Si–rich–SiO2, followed by pure thermal annealing or by infrared laser irradiation. The optical absorption and the electrical transport of Si:O films can be continuously and independently modulated by acting on different parameters. The light absorption increases with the Si content, determining an optical bandgap which can be continuously modulated into the 2.6–1.6 eV range. The electrical resistivity of Si:O films can be varied among five decades, being essentially dominated by the number of Si grains and by the doping. An extensive study on the electrical properties of the multilayer structure under dark and solar light exposure in conditions is discussed. The electrical data demonstrate that the current transport in such systems is mediated by tunnel effect, and the lowest effective energy barrier limiting the carrier transport has been found to be 1.7 eV. These data can be profitably used to better implement Si quantum dots for future photovoltaic technologies.