Multiexciton Generation in Seeded Nanorods

ABSTRACT: The stochastic formulation of multiexciton generation (MEG) rates is extended to provide access to MEG efficiencies in nanostructures containing thousands of atoms. The formalism is applied to a series of CdSe/CdS seeded nanorod heterostructures with different core and shell dimensions. At energies above 3Eg (where Eg is the band gap), the MEG yield increases with decreasing core size, as expected for spherical nanocrystals. Surprisingly, this behavior is reversed for energies below this value, and is explained by the dependence of the density of states near the valence band edge, which increases with the core diameter. Our predictions indicate that the onset of MEG can be shifted to lower energies by manipulating the density of states in complex nanostructure geometries. SECTION: Physical Processes in Nanomaterials and Nanostructures Multiexciton generation by which more than a singleelectron−hole pair is generated from a single photon upon optical excitation is a promising direction to collect “hot” carriers, potentially increasing photovoltaic power conversion efficiencies in solar cells to above 45%.1,2 It is common t