Plasmonic photovoltaics

To date, little systematic thought has been given to the question of how plasmon excitation and light localization might be exploited to advantage in photovoltaics. Using insights derived from the other phenomena studied in the plasmonics field, we outline approaches to dramatically modify the light absorption and carrier collection characteristics of photovoltaic materials and devices. Conventionally, photovoltaic absorbers must be optically 'thick' to enable nearly complete light absorption and photocarrier current collection. They are usually semiconductors whose thickness is typically several times the optical absorption length. For silicon, this thickness is greater than 100 microns, and it is several microns for direct bandgap compound semiconductors, and high efficiency cells must have minority carrier diffusion lengths several times the material thickness. Thus solar cell design and material synthesis considerations are strongly dictated by this simple optical thickness requirement. Dramatically reducing the absorber layer thickness could significantly expand the range and quality of absorber materials that are suitable for photovoltaic devices by, e.g., enabling efficient photocarrier collection across short distances in low dimensional structures such as quantum dots or quantum wells, and also in polycrystalline thin semiconductor films with very low minority carrier diffusion lengths.