Universal Size-Dependent Trend in Auger Recombination in Direct-Gap and Indirect-Gap Semiconductor Nanocrystals

Abstract

We report the first experimental observation of a striking convergence of Auger recombination rates in nanocrystals of both direct- (InAs, PbSe, CdSe) and indirect-gap (Ge) semiconductors, which is in contrast to a dramatic difference (by up to 4-5 orders of magnitude) in the Auger decay rates in respective bulk solids. To rationalize this finding, we invoke the effect of confinement-induced mixing between states with different translational momenta, which diminishes the impact of the bulk-semiconductor band structure on multiexciton interactions in nanocrystalline materials.

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…The timescale of Auger processes is typically on the order of 1-100 ps in single component NCs such as PbSe [199], Si [173], PbS [202], CdTe [203], Ge [204], InAs [205], or Pb-perovskites [161]. The Auger timescales in NCs are faster than those in the corresponding bulk material [204].…”

“…As discussed above, Auger processes in NCs are rapid and efficient because of spatial confinement of charge carriers. Therefore, the most obvious way to reduce Auger recombination rates is to increase the size of NCs [199,201,204,211,218]. However, this may not always be a desired strategy if one wants to make use of quantum confinement effects to tune the electronic properties of NCs.…”

“…Not only do these methods offer control over the charge state of QDs, they also allow for statistically significant measurements on entire ensembles [211], while single-NC experiments are necessarily limited to a small number of NCs. Ensemble transient absorption experiments are most commonly used to study multi-exciton dynamics in NCs [161,173,199,[203][204][205]. Analysis of the fast photoluminescence decay components of NCs under strong excitation can also provide information about multi-exciton decay rates [170,212].…”

Interfacial engineering of core/shell heterostructured nanocrystal quantum dots for light-emitting applications

“…For trions, the recombination of one electron and one hole yields a hot electron (or hole) via AR (Figure 2(a,b)). AR universally takes place in homogeneous (core-only) NQDs regardless of their band structure (direct vs. indirect) or bandgap [39], with a characteristic time scale of 10-100 ps (Figure 2c), far exceeding the radiative recombination rates of charge carriers.…”

Multiple exciton generation in quantum dot-based solar cells

“…As solution-based measurements do not capture all parameters relevant for a material to perform in solar cells, it remains to be seen how efficiencies from the two different environments will correlate. For instance, while increasing the quantum confinement has been shown to boost the efficiency of MEG, it also increases the rate of Auger recombination [52,53]. On the system level (i.e.…”