Research ArticleMATERIALS SCIENCE

Nanoscale mapping of chemical composition in organic-inorganic hybrid perovskite films

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Science Advances  25 Oct 2019:
Vol. 5, no. 10, eaaw6619
DOI: 10.1126/sciadv.aaw6619
  • Fig. 1 Nano-FTIR analysis of OIHP films.

    (A) Synchrotron broadband IR radiation is focused onto a metallic tip that tightly confines the fields at its apex for further interaction with the sample surface in standard tapping-mode AFM. AFM mapping retrieves nanoscale morphology (B) and IR broadband intensity (C) of individual grains in the ~150-nm-thick OIHP film. The IR broadband image (C) reveals changes in the vibrational response of specific OIHP grain boundaries that are further associated to early stages of organic depletion in the film. Scale bar, 200 nm.

  • Fig. 2 Topography and IR broadband imaging of the perovskites.

    Topography images (5 μm by 5 μm) of (A) CsFAMA and (D) CsFAMA degraded samples. The topography of the CsFAMA sample shows an even background layer with grains ranging from few to several hundreds of nanometers. The IR broadband image revealed an inhomogeneity in vibrational activity. Particles with stronger activity are associated with higher height observed in the region highlighted by the white dashed square a in (A) and (B), but nanoparticles with stronger activity not associated with higher height in the topography image as highlighted in square b are also observed. The induced degradation led to a growth of the grains, and the vibrational activity became more intense (E). From the IR broadband intensity histograms, there is a shift in the intensity from 0.36 mV in the CsFAMA sample (C) to 0.48 mV in the CsFAMA degraded sample (F). Scale bars, 1 μm.

  • Fig. 3 ATR-FTIR and nano-FTIR comparison of perovskites.

    (A) Far-field ATR-FTIR absorbance of MAPbI3 (top) and CsFAMA (bottom) perovskite films. The main molecular absorption of MA at 1470 cm−1 (symmetric NH3+ stretching) is very low in CsFAMA perovskite related to the molecular ratio between MA and FA. In the CsFAMA spectrum, the main molecular absorption around 1700 cm−1 is attributed to antisymmetric C-N stretching of the FA molecule. Nano-FTIR absorbance spectrum (B) and respective ATR-FTIR far-field spectrum (C) of a 370-nm-thick CsFAMA perovskite film. a.u., arbitrary units.

  • Fig. 4 Nanoscale chemical composition investigation by nano-FTIR.

    (A and E) AFM topography map (1 μm by 1 μm) of pristine CsFAMA and degraded CsFAMA perovskites, respectively. (B and F) Respective IR broadband images revealing heterogeneity in vibrational activity. Topography and IR broadband response do not completely correlate, as shown by the profiles in (C) and (G) related to pristine and degraded CsFAMA, respectively. (D and H) Nano-FTIR point spectra from the regions marked by numbers in (A), (B), (E), and (F). The characteristic vibrational mode of FA shows up only in grains with a weaker IR broadband response. For the degraded CsFAMA (H), the FA vibrational mode is less pronounced. The location 3′ is one of the few where the FA mode can be seen outside isolated grains. Scale bars, 200 nm.

  • Fig. 5 Structural characterization through high-resolution XRD.

    Crystal structure of black perovskite (α-phase) with a cubic structure (Pm3m space group), yellow FAPbI3 nonperovskite (δ-phase or 2H polytype) with a hexagonal structure (P63mc space group), and lead iodide (PbI2) with a hexagonal structure (Pm1 space group). The high-resolution diffractogram (A) of the CsFAMA sample confirms the α-phase perovskite and lead iodide in smaller quantity. The intensity of the PbI2 diffraction peak (B) of the CsFAMA degraded sample increased. The complete XRD of the CsFAMA degraded sample is available in the Supplementary Materials (fig. S4). The high-resolution XRD measurements were performed at 7 keV.

  • Fig. 6 Nanoscale chemical composition investigation by nano-FTIR of FAMA perovskite.

    (A and B) AFM topography map (5 μm by 5 μm) of FAMA perovskite and IR broadband image, respectively (scale bars, 200 nm). (C and D) Respective 1 μm by 1 μm images revealing heterogeneity in vibrational activity similar to pristine CsFAMA perovskite (scale bars, 200 nm). (E) Profiles of the topography and IR broadband. (F) Nano-FTIR point spectra from the regions marked in (C) and (D) reveal the presence of vibrational mode of FA in all marked locations. (G) The XRD pattern reveals that the FAMA sample is composed mostly of cubic perovskite, hexagonal phases, and PbI2 in less quantity. The high-resolution XRD measurements were performed at 7 keV.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaaw6619/DC1

    Perovskite preparation

    Solar cell characterization

    Fig. S1. Photovoltaic performance of CsFAMA solar cell.

    Fig. S2. High-resolution cross-sectional SEM image of the device.

    Fig. S3. Nano-FTIR of the intentionally degraded CsFAMA film at 100°C for 30 min.

    Fig. S4. High-resolution XRD pattern of the CsFAMA degraded perovskite sample deposited onto Si/Au substrate.

    Fig. S5. Comparison between intensity of the spectra collected at different regions of the FAMA film.

    Table S1. Film composition as obtained from Rietveld refinement using the software MAUD.

  • Supplementary Materials

    This PDF file includes:

    • Perovskite preparation
    • Solar cell characterization
    • Fig. S1. Photovoltaic performance of CsFAMA solar cell.
    • Fig. S2. High-resolution cross-sectional SEM image of the device.
    • Fig. S3. Nano-FTIR of the intentionally degraded CsFAMA film at 100°C for 30 min.
    • Fig. S4. High-resolution XRD pattern of the CsFAMA degraded perovskite sample deposited onto Si/Au substrate.
    • Fig. S5. Comparison between intensity of the spectra collected at different regions of the FAMA film.
    • Table S1. Film composition as obtained from Rietveld refinement using the software MAUD.

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