As photovoltaics (PV) cost reduction driven by economies of scale is approaching a limit, technological breakthroughs are likely to become again the next driver for further growth. In this paper, we review the most significant photovoltaic (PV) device technologies. First, commercially available cells and modules are briefly surveyed, focusing on the innovations that have recently reached the market, both in silicon-based and thin-film devices. We then identify some significant pre-market technologies such as organic PV and dye-sensitized solar cells, outlining the advantages as well as the obstacles that still hinder large-scale commercialization. A critical review is finally presented for the most promising approaches and some emerging technologies currently under investigation for simultaneously meeting the three key objectives in PV research, all aiming at further reducing the cost per kWh: low fabrication cost, systems integration, and overcoming the standard limit for photoconversion efficiency. All approaches heavily rely on nanotechnology, as the key mechanisms involved in PV conversion occur at the nanoscale.
