Spectral and dynamic analysis of CsPbBr3 perovskite nanocrystals with enhanced water stability using sodium passivation

Abstract

Sodium (Na) passivated CsPbBr3 nanocrystals (NCs) are synthesized using a modified ligand-assisted reprecipitation method at room temperature. With Na element introducing, small blue-shift absorption and photoluminescence (PL) are observed due to the surface passivation of NCs. The Na passivated NCs with the PL quantum yield of 66% have the improvement of water and thermal stability, with the reduction of 20% comparing with initial PL intensity in water/n-hexane after 12 h and a higher exciton binding energy of 150.8 meV. The spectral and dynamic excitonic recombination for Na: CsPbBr3 NCs are detected by time-resolved PL and transient absorption spectroscopy. The dynamics indicate that the coupling between the lowest excited state and exciton trapping state has significantly enhanced exciton recombination efficiency for Na: CsPbBr3 NCs. It can be observed that faster PL lifetime exists for CsPbBr3 NCs than that of Na: CsPbBr3 NCs in water/n-hexane, which indicates surface defects passivated through sodium incorporation. Na: CsPbBr3 NCs dispersing in NaBr aqueous/nonpolar solution remain bright after 60 days. The obtained results demonstrate that the effective strategies via sodium passivation can improve emission efficiency and stability of perovskite NCs, making them superior potential materials in optoelectronic applications.