Stabilization and Fluorescence Enhancement of CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals with Tungstosilicic Acid

It is still challenging to achieve both good stability and high PLQYs for perovskite NCs because of their ionic nature and structural defects. In this work, tungstosilicic acid (TSA) is used for the surface passivation of cesium lead halide perovskite NCs. Near-unity PLQY is achieved for CsPbBr3 NCs after surface passivation with a suitable amount of TSA. XRD in conjunction with XPS analysis shows that TSA binds hydrophobic chains of OAm onto the surface of CsPbBr3 NCs. XPS results also demonstrate that TSA passivation can change the charge distribution of the cations on the surface layers, which can enhance the interaction with surface traps. PL decay analysis reveals that trap states arising from the surface defects are significantly decreased after TSA passivation. TSA-passivated CsPbBr3 NCs demonstrate long-term ambient stability and good resistances to polar solvents and maintain about 80% of their initial PL intensity after storage under ambient conditions for 50 days. It is further found that TSA passivation is able to improve the PLQYs of a broad spectrum of CsPbX3 (X = Cl, Br, I) NCs without hindering the tunability of the band gaps and PL colors of CsPbX3 NCs via anion exchange.