Room-temperature surface engineering of CuInS2 nanocrystals: synergistic effects of ionic salts and dodecanethiol for enhanced optical properties

Abstract

Copper indium sulfide (CIS) quantum dots are promising non-toxic NIR emitters, but low photoluminescence quantum yield from surface defects and trap-assisted recombination limit their use, while core/shell approaches increase size and heterogeneity. Herein, we report a rapid, room-temperature post-synthetic treatment that overcomes these long-standing bottlenecks. Exposure of sub-2 nm CIS nanocrystals to Zn²⁺ or Cd²⁺ salts in a biphasic system, followed by thiol-based surface passivation, yields a remarkable enhancement in PLQY and excited-state carrier lifetime while minimally altering the intrinsic emission linewidth and core size. The strategy relies on controlled defect passivation rather than shell growth, effectively suppressing nonradiative pathways without inducing alloy-driven spectral shifts or particle coarsening. Notably, both chalcopyrite and wurtzite CIS nanocrystals respond favorably to this treatment across the visible-to-NIR window, demonstrating its broad applicability. While Cd²⁺ delivers the highest optical improvement, Zn²⁺ offers a nontoxic and sustainable alternative suitable for biological use. This work establishes a scalable defect-engineering route that decouples quantum yield enhancement from particle size growth, unlocking a new design framework for ultrasmall, bright, NIR-emitting CIS nanocrystals. The resulting materials may serve as compact emitters for bioimaging applications where renal clearance is desirable.