Abstract:
Both the first generation crystalline  Si and the second generation noncrystalline Si thin film solar cells dominate the current photovoltaic (PV) industry. The third generation nanotechnology approaches aim to decrease costs to well below 1.0 USD/W level of second generation PVs to 0.5 USD/W, potentially to 0.2 USD/W or better, by significantly increasing efficiencies but maintaining the economic and environmental cost advantages of thinfilm deposition techniques. In this paper,  we present a brief review on the recent achievements in Si nanocrystalline and nanowire solar cells as the future PV industry may belong to these nanostructured Si solar cells. The emphasis is on hydrogenated nanocrystalline silicon (ncSi:H) tandem thin film solar cells with the band gap tuned by the dot size, the preliminary application of Si nanowire arrays in planar Si solar cells and radial Si solar cell concept including single nanowire Si solar cells, and multiple exciton generation ncSi:H hot carrier solar cells.

Key words: Nobel Prize, surface chemistry, ammonia synthesis, CO oxidation ,  Si solar cell, nanocrystalline, nanowire, multiple exciton generation