Research ArticleSURFACE CHEMISTRY

Unconventional route to dual-shelled organolead halide perovskite nanocrystals with controlled dimensions, surface chemistry, and stabilities

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Science Advances  29 Nov 2019:
Vol. 5, no. 11, eaax4424
DOI: 10.1126/sciadv.aax4424
  • Fig. 1 Stepwise representation of the synthetic route to PS-capped MAPbBr3/SiO2 core/shell NCs and PEO-capped MAPbBr3/SiO2 core/shell NCs by exploiting star-like P4VP-b-PtBA-b-PS and P4VP-b-PtBA-b-PEO as nanoreactors, respectively.

    CD, cyclodextrin; BMP, 2-bromo-2-methylpropionate; and TOABr, tetraoctylammonium bromide.

  • Fig. 2 TEM images of PEO-capped MAPbBr3/SiO2 core/shell NCs.

    (A) MAPbBr3 core diameter of 6.1 ± 0.3 nm and SiO2 shell thickness of 8.9 ± 0.4 nm, crafted by capitalizing on star-like P4VP-b-PtBA-b-PEO (Sample A in Table 1) as nanoreactor, and (B) MAPbBr3 core diameter of 6.8 ± 0.3 nm and SiO2 shell thickness of 8.0 ± 0.3 nm, crafted by using star-like P4VP-b-PtBA-b-PS (Sample C in Table 1) as nanoreactor.

  • Fig. 3 Structure and optical characterization of PEO-capped MAPbBr3/SiO2 core/shell NCs.

    (A) XRD patterns of MAPbBr3/SiO2 core/shell NCs capped with PEO, MAPbBr3 core NCs capped with PAA-b-PEO, and pure bulk SiO2. (B) PL spectra of MAPbBr3 core NC before and after the SiO2 shell coating dispersed in toluene. a.u., arbitrary units. (C) Schematic illustration of direct conversion of PbI2 into MAPbI3. (D) Repeated washing of PEO-capped MAPbBr3/SiO2 core/shell NCs using n-hexane as a precipitant and toluene as a good solvent. The decrease in PL intensity in (B) and (D) is due to the change in the NC concentration. (E) Time-resolved PL decay traces of PEO-b-PtBA–capped MAPbBr3 NCs (τ1 = 7.6 ns, τ2 = 25.4 ns, and τave = 17.6 ns) and PEO-capped MAPbBr3/SiO2 core/shell NCs (τ1 = 9.8 ns, τ2 = 29.6 ns, and τave = 19.4 ns), where black and blue curves are the corresponding biexponential fits, respectively.

  • Fig. 4 Investigation into an array of stabilities of PS-capped MAPbBr3/SiO2 core/shell NCs.

    (A) Colloidal stability during repeated solvent washing using n-hexane as a precipitant and toluene as a solvent. The decrease in PL intensity is due to the change in the NC concentration. (B) Chemical composition stability of PS-capped MAPbBr3/SiO2 core/shell NCs (λPS-capped MAPbBr3/SiO2 = 529 nm) mixed with PEO-capped MAPbI3 NCs (λPEO-capped MAPbI3 = 697 nm) in toluene. (C) Photostability of PS-capped MAPbBr3/SiO2 core/shell NC toluene solution in response to continuous illumination of 365-nm UV light at RH of 55 ± 2%. (D) Moisture stability of PS-capped MAPbBr3/SiO2 core/shell NC toluene solution with varied PS chain lengths (i.e., MWPS = 5K and 10K) stored under different moisture conditions (i.e., RH = 50 and 75%). (E) Moisture stability (i.e., RH = 80%) and photostability (under 450-nm illumination) of 10K PS-capped MAPbBr3/SiO2 core/shell NC thin film stored without inert gas protection.

  • Fig. 5 Digital images of evolution of PS-capped MAPbBr3/SiO2 core/shell NC thin film spin coated on a glass substrate immersed into DI water.

    (A) 0 min, (B) 15 min, and (C) 30 min. (D) Schematic illustration of dual-shelled MAPbBr3 NC (i.e., PS-ligated MAPbBr3/SiO2 core/shell NC) in solution (left) and in thin film state (right) when in contact with water. The outer PS chains collapses, forming a dense PS shell situated on the SiO2 shell surface to further effectively distance water from the MAPbBr3 core and result in enhanced water stability.

  • Table 1 Summary of MWs of amphiphilic star-like P4VP-b-PtBA-b-PEO and P4VP-b-PtBA-b-PS triblock copolymers and the corresponding dimension of polymer-capped MAPbBr3/SiO2 core/shell NCs.

    SamplesMn,P4VP*
    (kg/mol)
    Mn,PtBA
    (kg/mol)
    Mn,PS
    (kg/mol)
    Mn,PEO§ (kg/mol)PDI§Dimensions of MAPbBr3/SiO2 core/shell
    NCs (core diameter/shell thickness) (nm)
    Sample A800014,60050001.156.1 ± 0.3/8.9 ± 0.4
    Sample B930021,60050001.188.0 ± 0.3/9.8 ± 0.4
    Sample C850013,8005,0001.196.8 ± 0.3/8.0 ± 0.3
    Sample D780015,60010,0001.196.0 ± 0.4/8.9 ± 0.5

    *Number average MW of the inner P4VP block (Mn,P4VP) was calculated from 1H NMR data. The calculation method was adapted from a previous work (33).

    †Number average MW, Mn of each PtBA block calculated on the basis of 1H NMR data from the MW difference between PtBA block and P4VP block. The intermediate PtBA block can be calculated by the following equation Mn,PtBA = Aa/9Ab/4 × Mn,P4VP × MtBAM4VP, where Mn,P4VP and M4VP are MWs of the inner P4VP block and the 4VP monomer, respectively. Ab and Aa are the integral area of the protons in the pyridine group of P4VP block and the integral area of methyl protons in the tert-butyl group of PtBA block, respectively. Mn,PtBA and Mn,P4VP are MWs of the intermediate PtBA block and the inner P4VP block, respectively. Ae and Ab are the integral area of methyl protons in the tert-butyl group of PtBA block and the integral area of protons in the pyridine group of P4VP block, respectively. MtBA and M4VP are MWs of the tBA monomer and the 4VP monomer, respectively.

    ‡Number average MW of the outer PS block was calculated from 1H NMR data based on the following equation Mn,PS = (9×AbAa × MPtBAMtBA  4 × MP4VPM4VP) × MSt5, where Mn,PS, Mn,PtBA, and Mn,P4VP are the MWs of the outer PS block, intermediate PtBA block, and inner P4VP block, respectively. Aa and Ab are the integral area of methyl protons in the tert-butyl group of PtBA block and the integral area of protons in the phenyl group and the pyridine group of PS and P4VP blocks, respectively. MSt, MtBA, and MP4VP are MWs of St, tBA, and 4VP monomers, respectively.

    §PDI was recorded by DMF GPC.

    The core diameter and shell thickness of core/shell NCs were determined by performing image analysis on TEM images of MAPbBr3/SiO2 core/shell NCs.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax4424/DC1

      Experimental Section

      Table S1. Dipole moment and normalized polarity of common organic solvents.

      Fig. S1. Characterization of macroinitiator and various 21-armed star-like homopolymer and copolymers.

      Fig. S2. NMR spectra of polymers and DLS measurements of star-like P4VP-b-PtBA-b-PEO copolymer in different solvents.

      Fig. S3. Structural characterization of PNCs prepared by conventional method and star-like block copolymer nanoreactor strategy, respectively.

      Fig. S4. XRD patterns, UV-vis absorption and PL spectra, and TEM images of perovskites.

      Fig. S5. UV absorption spectra of MAPbI3 PNCs prepared by different methods.

      Fig. S6. XRD patterns of MAPbI3 prepared by reacting MAI with PbI2 dissolved in different solvents.

      Fig. S7. Stability of MAPbX3 PNCs synthesized by conventional method (i.e., LARP) upon exposure to various common polar organic solvents by the addition of a designated volume of these solvents into the purified PNC toluene solution.

      Fig. S8. MAPbBr3 PNCs prepared by conventional method when exposed to repeated solvent washing and mixing with PNCs of different compositions.

      Fig. S9. Digital images of evolution of PS-capped MAPbBr3/SiO2 core/shell NCs dispersed in toluene with the addition of 20% water (by volume) under 365-nm UV light.

    • Supplementary Materials

      This PDF file includes:

      • Experimental Section
      • Table S1. Dipole moment and normalized polarity of common organic solvents.
      • Fig. S1. Characterization of macroinitiator and various 21-armed star-like homopolymer and copolymers.
      • Fig. S2. NMR spectra of polymers and DLS measurements of star-like P4VP-b-PtBA-b-PEO copolymer in different solvents.
      • Fig. S3. Structural characterization of PNCs prepared by conventional method and star-like block copolymer nanoreactor strategy, respectively.
      • Fig. S4. XRD patterns, UV-vis absorption and PL spectra, and TEM images of perovskites.
      • Fig. S5. UV absorption spectra of MAPbI3 PNCs prepared by different methods.
      • Fig. S6. XRD patterns of MAPbI3 prepared by reacting MAI with PbI2 dissolved in different solvents.
      • Fig. S7. Stability of MAPbX3 PNCs synthesized by conventional method (i.e., LARP) upon exposure to various common polar organic solvents by the addition of a designated volume of these solvents into the purified PNC toluene solution.
      • Fig. S8. MAPbBr3 PNCs prepared by conventional method when exposed to repeated solvent washing and mixing with PNCs of different compositions.
      • Fig. S9. Digital images of evolution of PS-capped MAPbBr3/SiO2 core/shell NCs dispersed in toluene with the addition of 20% water (by volume) under 365-nm UV light.

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