<Abstrate>

Cesium lead halide perovskite quantum dots (PQDs) have emerged as a promising

new platform for lighting applications. However, to date, light emitting diodes (LED)

based on these materials exhibit limited efficiencies. One hypothesized limiting factor

is fast nonradiative multiexciton Auger recombination. Using ultrafast spectroscopic

techniques, we investigate multicarrier interaction and recombination mechanisms in

cesium lead halide PQDs. By mapping the dependence of the biexciton Auger lifetime

and the biexciton binding energy on nanomaterial size and composition, we find

unusually strong Coulomb interactions among multiexcitons in PQDs. This results

in weakly emissive biexcitons and trions, and accounts for low light emission

efficiencies. We observe that, for strong confinement, the biexciton lifetime depends

linearly on the PQD volume. This dependence becomes sublinear in the weak

confinement regime as the PQD size increases beyond the Bohr radius. We demonstrate

that Auger recombination is faster in PQDs compared to CdSe nanoparticles having

the same volume, suggesting a stronger Coulombic interaction in the PQDs.

We confirm this by demonstrating an increased biexciton binding energy, which reaches

a maximum of about 100 meV, fully three times larger than in CdSe quantum dots.

The biexciton shift can lead to low-threshold optical gain in these materials. These

findings also suggest that materials engineering to reduce Coulombic interaction in

cesium lead halide PQDs could improve prospects for high efficiency optoelectronic

devices. Core–shell structures, in particular type-II nanostructures, which are known

to reduce the bandedge Coulomb interaction in CdSe/CdS, could beneficially be

applied to PQDs with the goal of increasing their potential in lighting applications.

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