Ultrafast photophysical process of bi-exciton Auger recombination in CuInS2 quantum dots studied by transient-absorption spectroscopy

Auger recombination is an ultrafast and unnegligible photophysical process in colloidal semiconductor quantum dots (QDs) due to competition with charge separation or radiative recombination processes, pivotal for their applications ranging from bio-labeling, light-emitting diodes, QD lasing to solar energy conversion. Among diverse QDs, ternary chalcopyrite is recently receiving significant attention for its heavy-metal free property and remarkable optical performance. Given deficient understanding of the Auger process for ternary chalcopyrite QDs, CuInS₂ QDs with various sizes are synthesized as a representative and the bi-exciton lifetime (τ_BX) is derived by virtue of ultrafast time resolved absorption spectrum. The trend of τ_BX varying with size is consistent with the universal scaling of τ_BX versus QD volume (V): τ_BX = γV. The scaling factor γ is 6.6 ± 0.5 ps·nm^-3 for CuInS₂ QDs, and the bi-exciton Auger lifetime is 4-5 times slower than typical CdSe QDs with the same volume, suggesting reduced Auger recombination rate in ternary chalcopyrite. This work facilitates clearer understanding of Auger process and provides further insight for rational design of light-harvesting and emitting devices based on ternary chalcopyrite QDs.