APPLICATIONS  |  PEROVSKITE CRYSTALS


 

HYPERSPECTRAL STUDY OF AGED PEROVSKITE CRYSTALS

The search for flexible, cheap, and easy to process photovoltaic materials took a new turn in the past years with the rapid evolution of organometallic perovskite solar cells. These new type of cells might soon dethrone the current champion of photovoltaics: silicon. Their high carrier mobility, strong absorption in the visible and tunable band gap make it an ideal candidate for the production of low cost solar panels. However, there is one drawback: their stability is precarious and their current life time (~ 2000 solar peak hours) is not even near silicon’s performances (~ 52 000 hours in bright sunlight). If research groups want to take to the market this new star of photovoltaics, a better understanding of the photophysics and the degradation mechanisms is essential.

Photon etc’s global hyperspectral imaging platform (IMA™) is perfectly suited to find the answers to the questions scientists have been asking themselves about perovskite’s outstanding properties. IMA™ can characterize rapidly the structural properties of 2D and 3D perovskite crystals as well as complete photovoltaic devices through optical measurements. IMA™ captures images wavelength after wavelength and provides spectrally resolved luminescence and transmittance maps over large areas (100 x 100 µm2 - 1 x 1 mm) without any spatial scanning and with a high spatial resolution (~µm).

We present here hyperspectral data of perovskite crystals taken with IMA™. These results were acquired in collaboration with Prof. David Cooke (McGill University) and Prof Mercouri Kanatzidis (Northwestern University). Figure 1 presents hyperspectral PL data of a perovskite. In only a few minutes, a million PL spectra from 550-900 nm (with 1 nm step size) were acquired over an area of 670 x 900 µm2. Figure 1 (a) and (b) show two different monochromatic PL images taken at 625 nm and 750 nm respectively. It is possible to observe the different spectral features on figure 1 (c) and a map of the emission peak shift taken over a specific region (see figure 1 (d)).

Figure 2 presents hyperspectral transmittance data of a different perovskite sample over a 180 x 134 µmarea. Figure 3 presents the PL data taken over the same area as the one presented in figure 2. Figure 3 (b) presents spectral features of designated areas of Figure 3 (a) while a map of the emission peak shift over the same field of view is shown on figure 3 (c). In a few minutes, the whole spectral content of large area of perovskite crystal is acquired and its structural features can be easily.

Hyperspectral global imaging gives quickly access to the spatial distribution of:

  • surface defects
  • grain boundaries
  • phase segregation
  • disorder

This efficient method provides a deep characterization of perovskite microstructure and will significantly help the understanding of the degradation phenomenon in those materials and bring them one step closer to commercialization.

 

FIG 1. Hyperspectral photoluminescence data acquired with IMA™ (532 nm excitation laser). (a) Monochromatic PL image at 625 nm, (b) monochromatic PL image at 750 nm, (c) PL spectra extracted from different regions on the sample (see corresponding colored arrows on (a)), (d) map of the PL shift.

FIG 2. Hyperspectral transmittance images taken with IMA™. (a) Monochromatic transmittance image at 610 nm, (b) monochromatic transmittance image at 840 nm, (c) transmittance spectra extracted from different regions on the sample (see corresponding colored arrows on (a-b)).

FIG 3. Hyperspectral photoluminescence images acquired with IMA™ (532 nm excitation laser). (a) Monochromatic PL image at 770 nm, (b) PL spectra extracted from different regions on the sample (see corresponding colored arrows (a)), (c) map of the PL shift.

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