Organolead Halide Perovskite Nanocrystals: Branched Capping Ligands Control Crystal Size and Stability

Abstract

These are not the final page numbers! Ü Ü uniform. The low absorption/emission intensity of PNC supernatant is attributed to the low concentration of PNCs. This indicates that the as-formed PNCs can be easily collected by centrifugation (Supporting Information, Figure S5 b), which is desirable for cleaning and postprocessing in various applications.To explain the different capping effects of OA and APTES, we propose the following mechanism based on a dissolution-precipitation model (Figure 4 c). The dissolved precursors precipitate as PNCs at the DMF-toluene interface when the DMF precursor solution is injected into toluene. With OA as the capping ligand, the OA molecules adsorbed on the surface of the formed PNCs and PNSs diffuse from DMF to toluene, along with the products. However, the chain configuration of OA molecules cannot effectively prevent the products from dissolving back into DMF across the DMFtoluene interface and some OA ligands remain in the toluene phase because of their non-polar nature. The loss of OA ligands will result in a lack of ligands in the DMF phase, leading to the formation of large particles in the next round of precipitation. This effect becomes more pronounced when the concentrations of the precursors is high. On the contrary, the strong steric hindrance of APTES and the formation of silica can prohibit the dissolution of the as-formed PNCs back into DMF, which helps to maintain the original structural and optical properties of PNCs. Nevertheless, the PNC APTES-20 sample began to flocculate after standing for a few minutes (Supporting Information, Figure S7) because of hydrolysis of Si-O-C 2 H 5 groups attached to the PNC APTES surface, which generate hydroxy (-OH) groups (as indicated by FTIR spectra), resulting in a change in polarity and hydrogen bonding of the ligands.Water-induced degradation is a major problem for organic metal halide perovskites because protons are captured by methylammonium.[8] Similarly, they are also unstable towards other protic solvents such as alcohols.We hypothesized that PNC APTES may exhibit better stability because of the strong steric hindrance and hydrolysis properties of APTES, which reduces the access of protic solvent molecules to the PNCs surface. To test the stability of PNC APTES in protic solvents, 0.5 mg mL À1 of PNC precipitate capped by different ligands was dispersed in ethanol (Supporting Information, Figure S9 a and b). No emission was observed by the naked eye for PNC OA and PNC OABr dispersed in ethanol, and all XRD peaks (Supporting Information, Figure S9 c) of the decomposed products belong to rhombic PbBr 2 (JCPDS#31-0679). However, the PNC APTES precipitate showed high fluorescence intensity after sonication in ethanol, indicating better stability of PNC APTES in protic solvents.Long term stability tests were also conducted in different protic and polar solvents. As shown in Figure 5 a, the relative PL intensity of the PNC APTES-16 precipitate in isopropanol remained almost 70 % after 2.5 h. However, PNC precipitate showed p...

Colloidal lead halide perovskite nanocrystals: synthesis, optical properties and applications

“…Very recently, we and others have demonstrated that the encapsulation of perovskite NCs in a polyhedral oligomeric silsesquioxane matrix or a mesoporous silica shell not only prevents this halide exchange, but also enhances the water resistivity of the NCs. [122][123][124][125] In addition, perovskite NCs are extremely sensitive and tend to degrade or transform in to other compounds (such as metallic lead) under exposure to electron beams. 25 The exact mechanisms of these transformations need to be investigated, as TEM studies are crucial for unambiguous characterization of the morphology of perovskite NCs.…”

Peptide‐Passivated Lead Halide Perovskite Nanocrystals Based on Synergistic Effect between Amino and Carboxylic Functional Groups

“…[6,23,31] It was found that the presence of oleic acid improves the outcome of the synthesis with amino ligands. [6,23,31] It was found that the presence of oleic acid improves the outcome of the synthesis with amino ligands.…”

“…In addition, because of the dominant Brsurface defects in PNCs, the PL enhancement is more sensitive to the amount of R′-NH 3 + than that of R-COO -, as the former should passivate the Brdefect sites. [31] (3 of 7) 1604018 It can be seen from the PL spectra in Figure 1 that the peak position of the main emission band shifts a lot when different carboxylic acids are used, which may be due to different degrees of steric hindrance from the carboxylic capping ligands.…”

Lead Halide Perovskite Nanocrystals in the Research Spotlight: Stability and Defect Tolerance

“…Employing different ligands to improve or change the properties of as-prepared materials is a very common strategy in the colloidal QD field, and this is particularly relevant to increasing the stability of LHP NCs given their innate sensitivity to water and other polar solvents. Figure 6a shows an attempt to use different ligands other than the commonly used OA or OLA by Luo et al 97 By using branched capping ligands, (3-aminopropyl) triethoxysilane (APTES) and polyhedral oligomeric silsesquioxane (POSS) PSS-[3-(2-aminoethyl)amino]propylheptaisobutyl substituted (NH 2 -POSS), the authors showed that APTES and POSS could be used as passivators and stabilizers of MAPbBr 3 NCs. PL monitoring under exposure to ethanol under UV lamp irradiation indicated enhanced stability when using those two ligands.…”

“…Adapted from ref (97). (b) PL of MAPbBr 3 NCs P AD–CB (in black) and P AD (in green) dispersed in toluene and in contact with water as a function of the irradiation time.…”