Efficient carrier multiplication and extraction in aqueous-processed giant CdTe-CdS nanocrystal bulk heterostructures

Auger recombination as an intrinsic mechanism for bypassing the 'phonon bottleneck' plays an important role in semiconductor quantum dots, which makes the possible carrier multiplication or multiple-exciton generation occurred in nanoscale. Here, we show that for aqueous-processed giant CdTe-CdS core-shell nanocrystal solids (the diameter of CdTe core is similar to 20 nm, larger than its bulk exciton Bohr radius of similar to 7.5 nm), it is a type-II structure with small band offsets and strong delocalization of electrons. Thus, there is an efficient carrier multiplication by Auger processes, in comparison with the exciton relaxation behaviors in reference films consisting of large CdTe quantum dots (the diameter is similar to 11 nm) synthesized by an oil-phase approach. The efficient carrier extractions are further demonstrated using TiO2 and MoO3 as carrier transport layers in CdTe-CdS nanocrystal depleted bulk heterostructures, and imbalanced carrier extraction efficiencies by TiO2 and MoO3 are revealed. Our findings unravel the fundamental photophysical mechanisms for the high-efficient all-solid nanocrystal photovoltaics based on aqueous-processed giant CdTe-CdS nanocrystal solids. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

This study investigates the Auger recombination mechanism for carrier multiplication in giant CdTe-CdS core-shell nanocrystal solids processed in water, compared with exciton relaxation behaviors in reference films of large CdTe quantum dots synthesized using an oil-phase approach. Efficient carrier extraction is demonstrated using carrier transport layers, revealing imbalanced carrier extraction efficiencies.