Photogeneration and recombination of multiexcitons in nanocrystal quantum dots in relation to solar energy conversion

A usual assumption is that absorption of a single photon by a material produces a single electron-hole pair (exciton), while the photon energy in excess of the energy gap is dissipated as heat. In 2004, we reported for the first time that nanocrystals of PbSe could respond to absorption of a single photon by producing two or more excitons with the unity probability (Phys. Rev. Lett. 92, 186601, 2004). More recently, we observed generation of up to seven excitons per absorbed photon (Nano Lett. 6, 424, 2006), which corresponds to the ultimate limit allowed by energy conservation for the excitation energy used in these measurements. This presentation discusses such aspects of multi-exciton generation in nanocrystals as characteristic time scales of this process, statistics of photogenerated multiexciton populations, the limits on photon-to-exciton conversion efficiencies, and implications of multiexciton generation in photovoltaics and photocatalysis.