Anion Exchange in Cesium Lead Halide Perovskite Nanocrystals via Radiation Chemistry of Halohydrocarbons

Abstract

Cesium halide lead (CsPbX 3 ) perovskite nanocrystals (NCs) have been extensively studied in recent years for their unique capability of postsynthesis anion exchange, providing facile tunability of band gaps and optical properties. In this work, we demonstrate for the first time a simple approach to the tunable anion exchange of CsPbX 3 perovskite NCs via radiation chemistry of inert halohydrocarbons. The anion exchange extents are monitored by shifting of fluorescence emission peaks and ultraviolet−visible absorbance edges and are precisely controlled by tuning the absorbed doses and the adjustable addition of halohydrocarbons. At the same absorbed doses, the anion exchange extents by halohydrocarbons are dependent on the linear attenuation coefficients of halohydrocarbons. Radiation-induced anion exchange can passivate defects in CsPbX 3 NCs, resulting in the fluorescence enhancement. The morphology of perovskite NCs almost remains intact after radiation-induced anion exchange.

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

“…According to the peak splitting at around 15°, the CsPbBr 3 NCs are identified as orthorhombic crystals (ICSD 97851 for CsPbBr 3 ). The XRD pattern of the cubic phase resembles that of the orthorhombic phase, except that the latter shows peak splitting at about 15° (2Θ) due to symmetry lowering . After TSA passivation, the crystalline structure of CsPbBr 3 NCs is not changed, but two diffraction peaks (2Θ = 6.1 and 8.2°) emerge (Figure a).…”

“…The XRD pattern of the cubic phase resembles that of the orthorhombic phase, except that the latter shows peak splitting at about 15°(2Θ) due to symmetry lowering. 8 After TSA passivation, the crystalline structure of CsPbBr 3 NCs is not changed, but two diffraction peaks (2Θ = 6.1 and 8.2°) emerge (Figure 3a). To determine the origin of the two peaks, we perform XRD analysis for TSA, Cs-ST, and OAm-ST and find that only OAm-ST shows nearly the same peaks (Figure 3c).…”

“…However, the band gaps and emission wavelengths of perovskite NCs with compact inert shells may not be tunable via anion exchange anymore. 8,29 Surface passivation can efficiently reduce the structural defects to improve the luminous properties. 10,23,25,26,30−35 Alkylammonium halides, inorganic salts, and ligand molecules that bind strongly to the surface of perovskite NCs were often used for the surface passivation of perovskite NCs according to the literature.…”

“…Cesium lead halide perovskite (CsPbX 3 , X = Cl, Br, I) nanocrystals (NCs) have been successfully applied in the fields of photodetectors, lasers, and particularly light-emitting diodes (LEDs) and solar cells − because of their unique characteristics, including tunable emission wavelengths, high photoluminescence quantum yields (PLQYs), and narrow emission peaks. − However, the PLQYs and structure/performance stability of CsPbX 3 NCs are significantly impaired by their ionic nature and inevitable structure defects originating from their rapid synthesis, ,, especially when facing natural environments with water or other polar solvents, light, and heat, − despite their high defect tolerance compared with semiconductor NCs. − …”

“…Various strategies have been developed to stabilize perovskite NCs, including surface passivation and constructing core–shell structures. − The latter is an effective strategy to coat the CsPbX 3 NCs with compact inert shells. − PbSO 4 , ZnS, SiO 2 , and other materials have been reported to be used as the shell materials. − This method can improve the long-term stability in harsh environments. However, the band gaps and emission wavelengths of perovskite NCs with compact inert shells may not be tunable via anion exchange anymore. , …”