Suppressing Tail Emission from AgIn_1-xGa_xS₂/AgGaS₂ Quantum Dots by GaI₃-Assisted Interface Reinforcement

Heteroepitaxy of AgGaS₂ (AGS) or GaS_x shells on AgIn_1-xGa_xS₂ (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 GaI₃ 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.