Enhanced blue photoluminescence and photostability of Cs3Bi2Br9 perovskite quantum dots via surface passivation with silver ions

Abstract

Lead halide perovskite quantum dots (QDs) with color tunability and narrow-band emissions are promising materials of nanophotonic and photoelectronic fields, but the lead toxicity and instability limit their practical applications. On the other hand, lead-free perovskite QDs suffer from the disadvantages of low photoluminescence quantum yields (PLQYs) and poor stability. Here, we demonstrate a green and facile method to synthesize a lead-free perovskite of Cs₃Bi₂Br₉ QDs with greatly improved optical properties and stability. With the introduction of Ag ions, the PLQY of the as-synthesized Cs₃Bi₂Br₉ QDs has been enhanced by 3.93 times, showing a blue emission at 413 nm. We suggest that the introduced Ag(I) complex fixes the bromide on the Cs₃Bi₂Br₉ QD surface, reduces the surface trap density, and thus efficiently passivates the surface. This passivation effect also regulates the exciton recombination process and leads to the increased probability of radiative deactivation. TEM and XPS analyses confirm the existence of Ag atoms on the surface of Cs₃Bi₂Br₉ QDs. Moreover, the effective passivation also improves the photostability of Cs₃Bi₂Br₉ QDs, resulting in 90% PL intensity being retained after 80 min of UV illumination under ambient conditions. We believe that the method used here provides an effective strategy to improve the fluorescence efficiency of lead-free perovskite QDs, which will create opportunities for their applications in lighting and displays.