Thick-shell colloidal quantum dots (QDs) are promising building blocks for solar technologies due to their size/composition/shape-tunable properties. However, most well-performed thick-shell QDs suffer from frequent use of toxic metal elements including Pb and Cd, and inadequate light absorption in the visible and near-infrared (NIR) region due to the wide bandgap of the shell. In this work, eco-friendly AgInSe2/AgInS2 core/shell QDs, which are optically active in the NIR region and are suitable candidates to fabricate devices for solar energy conversion, are developed. Direct synthesis suffers from simultaneously controlling the reactivity of multiple precursors, instead, a template-assisted cation exchange method is used. By modulating the monolayer growth of template QDs, gradient AgInSeS shell layers are incorporated into AgInSe2/AgInS2 QDs. The resulting AgInSe2/AgInSeS/AgInS2 exhibits better charge transfer than AgInSe2/AgInS2 due to their favorable electronic band alignment, as predicted by first-principle calculations and confirmed by transient fluorescence spectroscopy. The photoelectrochemical cells fabricated with AgInSe2/AgInSeS/AgInS2 QDs present ≈1.5-fold higher current density and better stability compared to AgInSe2/AgInS2. The findings define a promising approach toward multinary QDs and pave the way for engineering the QDs’ electronic band structures for solar-energy conversion.
