Sustained Biexciton Populations in Nanoshell Quantum Dots

Multiple-exciton (MX) generation is beneficial to many applications of semiconductors, including photo induced energy conversion, stimulated emission, and carrier multiplication. The utility of MX processes is generally enhanced in small-size semiconductor nanocrystals exhibiting the quantum confinement of photoinduced charges. Unfortunately, a reduced particle volume can also accelerate the nonradiative Auger decay of multiple excitations, greatly diminishing the MX feasibility in nanocrystal-based photovoltaic, laser, and photoelectrochemical devices. Here, we demonstrate that such Auger recombination of biexcitons could be suppressed through the use of a quantum-well (QW) nanoshell architecture. The reported nanoscale geometry effectively reduces Coulomb interactions between photoinduced charges underlying Auger decay. This leads to increased biexciton lifetimes, as was demonstrated in this work through ultrafast spectroscopy methods. In particular, we observed that the biexciton lifetime of CdSe-based QW nanoshells (CdS/CdSe/CdS) was increased more than 30 times relative to that of zero-dimensional CdSe NCs. The slower biexciton decay in QW nanoshells was attributed to a large confinement volume, which compared favorably to other existing MX architectures.