Suppressing Tail Emission from AgIn1–xGaxS2/AgGaS2 Quantum Dots by GaI3–Assisted Interface Reinforcement

Heteroepitaxy of AgGaS 2 (AGS) or GaS x shells on AgIn 1– x Ga x S 2 (AIGS) quantum dots (QDs) enables narrow band-edge emission with a near-unity photoluminescence quantum yield (QY). While this outcome is attributed to the passivation of donor–acceptor pair states on the surface, persistent tail emission, regardless of the QY, implies underlying interfacial defects in the AIGS/AGS QDs. Herein, we identify the latent compositional and crystallographic disorder at the core–shell interface originating from the surface instability of AIGS QDs. The strong coordination of oleylamine to group III cations promotes partial dissolution of the AIGS cores, resulting in a Ga-deficient, structurally disordered phase that contains interfacial donor states that are thermally mixed with the band-edge electron state. The incorporation of GaI 3 weakens the coordination of oleylamine to cations at the surface and in the dissolution products, thereby suppressing the disorder by fostering a Ga-rich environment. The suppressed tail emission, even at 80 K, highlights the importance of surface stabilization in eliminating the interfacial defects.