Electronic relaxation dynamics in colloidal semiconductor nanocrystals

Colloidal semiconductor heterostructures offer interesting ways of regulating and understanding carrier statics and dynamics. In strongly confined quantum dots, rapid electron cooling has been observed despite the large mismatch between electronic and phonon energies. The rapid carrier relaxation has been attributed to several alternate radiationless processes including electron-hole and electron-surfactant coupling as well as electron trapping. These relaxation processes are studied using various time resolved spectroscopic techniques. It is shown that heterostructures designed to control these processes can exhibit electronic relaxation rates over three orders of magnitude slower than bulk electronic relaxation rates. This corresponds to hot electron lifetimes longer than 1 ns. Phenomena such as the phonon bottleneck and hot electron extraction that will be described in this presentation offer possible routes to “third-generation” photovoltaics with potential efficiencies exceeding the Shockley-Queisser limit.