Surface Passivation of Bismuth-Based Perovskite Variant Quantum Dots To Achieve Efficient Blue Emission

Metal halide perovskite quantum dots (QDs) recently have attracted great research attentions. However, blue-emitting perovskite QDs generally suffer from low photoluminescence quantum yield (PLQY) because of easily formed defects and insufficient surface passivation. Replacement of lead with low toxicity elements is also preferred toward potential commercial applications. Here, we apply Cl-passivation to boost the PLQY of MA₃Bi₂Br₉ QDs to 54.1% at the wavelength of 422 nm, a new PLQY record for blue emissive, lead-free perovskite QDs. Because of the incompatible crystal structures between MA₃Bi₂Br₉ and MA₃Bi₂Cl₉ and the careful kinetic control during the synthesis, Cl^- anions are engineered to mainly locate on the surface of QDs acting as passivating ligands, which effectively suppress surface defects and enhance the PLQY. Our results highlight the potential of MA₃Bi₂Br₉ QDs for applications of phosphors, scintillators, and light-emitting diodes.