Publication date: 15th December 2025
Colloidal I-III-VI quantum dots (QDs) including AgInS2 are emerging as Restriction of Hazardous Substance (RoHS)-compliant emitters for next-generation optoelectronic technologies, offering compositional flexibility, tunable band gap, and strong chemical stability.1 AgInS2 feature a unique upper valence band structure with two energetically separated maxima at the Γ-point.2 Here, we explore intrinsic exciton and biexciton dynamics in AgInS2 QDs of different sizes (4-10 nm in diameter) by using ultrafast transient transmission spectroscopy. Although dominant nonradiative pathways and mid-gap donor-acceptor pair defects limit free-exciton emission in these QDs, we address this challenge by post-synthetic surface defect passivation at room temperature using dual ligands. As a result, AgInS2 QDs show narrow emission with photoluminescence quantum yield up to 56%. Exciton formation is associated with inter-valence band hole relaxation which slows with smaller QDs due to confinement effects. Interestingly, the biexciton-induced absorption evolves on a similar timescale as hole relaxation, indicating exciton to biexciton transitions involves different excitons during the relaxation process. Fluence-dependent pump-probe measurements further reveal fast biexciton decay in smaller QDs due to exciton-exciton annihilation. Together, our results demonstrate that highly emissive AgInS2 QDs can be achieved through dual-ligand passivation, and the exciton-biexciton dynamics is regulated by inter-valence-band hole relaxation, a feature distinctive to these QDs.
The Bavarian State Ministry of Science, Research, and the Arts through the grant “Solar Technologies go Hybrid (SolTech)".
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