Shell-Thickness-Dependent Biexciton Lifetime in Type I and Quasi-Type II CdSe@CdS Core/Shell Quantum Dots

Suppression of Auger recombination in colloidal quantum dots (QDs) is important for their many applications, ranging from biological tagging, QD lasing, to solar energy conversion. Although it has been reported that the biexciton Auger recombination time of core/shell QDs can be significantly prolonged compared to core-only QDs, a systematic investigation of their dependence on the shell thickness is lacking. In this work, using CdSe@CdS core/shell QDs as a model system, we investigated the shell thickness dependence of biexciton lifetimes in both type I and quasi-type II QDs, prepared using large and small core sizes, respectively. We observe a strong increase of biexciton lifetime with the shell thickness and a larger saturation volume in quasi-type II CdSe@CdS QDs, compared to type I CdSe@CdS QDs. These trends can be attributed to the different thickness dependences of electron–hole wave function overlaps in these materials, which reflect their different extents of conduction band electron delocalization. Our findings provide further insight for rational design of core/shell QDs with suppressed Auger recombination rates.