In Situ Formation of Zwitterionic Ligands: Changing the Passivation Paradigms of CsPbBr₃ Nanocrystals

Abstract

CsPbBr 3 nanocrystals (NCs) passivated by conventional lipophilic capping ligands suffer from colloidal and optical instability under ambient conditions, commonly due to the surface rearrangements induced by the polar solvents used for the NC purification steps. To avoid onerous postsynthetic approaches, ascertained as the only viable stability-improvement strategy, the surface passivation paradigms of as-prepared CsPbBr 3 NCs should be revisited. In this work, the addition of an extra halide source (8-bromooctanoic acid) to the typical CsPbBr 3 synthesis precursors and surfactants leads to the in situ formation of a zwitterionic ligand already before cesium injection. As a result, CsPbBr 3 NCs become insoluble in nonpolar hexane, with which they can be washed and purified, and form stable colloidal solutions in a relatively polar medium (dichloromethane), even when longly exposed to ambient conditions. The improved NC stability stems from the effective bidentate adsorption of the zwitterionic ligand on the perovskite surfaces, as supported by theoretical investigations. Furthermore, the bidentate functionalization of the zwitterionic ligand enables the obtainment of blue-emitting perovskite NCs with high PLQYs by UV-irradiation in dichloromethane, functioning as the photoinduced chlorine source.

Highly efficient silica coated perovskite nanocrystals with the assistance of ionic liquids for warm white LEDs

“…5,6,18–21 Unfortunately, the issue of their intrinsic instability toward humidity, polar solvents, heat, and light irradiation, which results from the ionic structure of perovskite NCs and the highly dynamic of surface ligands, has become the major obstacle on the road of commercial applications. 22,23…”

“…Recently, various strategies aimed at improving the stability of perovskite NCs have been developed, including surface engineering, compositional regulation, and shell encapsulation. 23–29 Among these above-mentioned strategies, encapsulating perovskite NCs with robust semiconductor shells ( e.g. , ZnS, 30,31 CdS, 32 Cs 4 PbBr 6 , 33 and CsPb 2 Br 5 34 ), oxide shells ( e.g.…”

“…5,6,[18][19][20][21] Unfortunately, the issue of their intrinsic instability toward humidity, polar solvents, heat, and light irradiation, which results from the ionic structure of perovskite NCs and the highly dynamic of surface ligands, has become the major obstacle on the road of commercial applications. 22,23 Recently, various strategies aimed at improving the stability of perovskite NCs have been developed, including surface engineering, compositional regulation, and shell encapsulation. [23][24][25][26][27][28][29] Among these above-mentioned strategies, encapsulating perovskite NCs with robust semiconductor shells (e.g., ZnS, 30,31 CdS, 32 Cs 4 PbBr 6 , 33 and CsPb 2 Br 5 34 ), oxide shells (e.g., TiO 2 , 35 SiO 2 , 28,29 ZrO 2 , 36 and Al 2 O 3 37 ), or organic shells (e.g., MOF 38 and polymers 39 ) is the most direct and efficient protocol to protect the NC surface.…”

Enhanced emission efficiency in doped CsPbBr3 perovskite nanocrystals: the role of ion valence

“…[6][7][8] Continually improving the luminescence efficiency of materials remains an important challenge facing future practical optoelectronic applications. [9][10][11][12][13] To enhance the luminous efficiency of perovskite NCs, several effective methods, such as surface passivation, [14][15][16][17][18] surface coating, 19,20 and metal ion doping, 21 have been proposed. Doping, the intentional introduction of heteroatoms into a targeted lattice, has great potential in regulating the optical properties of semiconductor materials.…”

“…6–8 Continually improving the luminescence efficiency of materials remains an important challenge facing future practical optoelectronic applications. 9–13 To enhance the luminous efficiency of perovskite NCs, several effective methods, such as surface passivation, 14–18 surface coating, 19,20 and metal ion doping, 21 have been proposed.…”