Assessing the Key Challenges of the Next Generation of Solar Cells

In the last 20 years commercial, scientific and societal efforts have pushed solar cells from costly niche markets to commercial equality with legacy energy sources. New studies carried out on perovskite solar cells have shown immense potential. Undoubtedly, this emerging range of material displays the strongest growth in terms of efficiency ever seen in the photovoltaics field.

Perovskite seems to be the ideal candidate for the next generation of solar technology because it is easy to manufacture through roll-to-roll processes, is relatively low-cost, and has a thickness of just ~0.5 µm. Despite this fact, the durability of perovskite is still preventing it from leaving the laboratory; surprisingly, its sensitivity to light and heat are among its weaknesses.

Perovskite Solar Cells

The microstructure of the perovskite solar cell influences its efficiency and this candidate can be developed through more improved understanding. In order to shed light on this material, researchers are turning to hyperspectral global imaging. This imaging technique gives in-depth information over millions of point on the surface of the material, within minutes or even seconds.

Reflectance, transmittance and luminescence images quantified at hundreds of wavelengths offer important physicochemical properties at the micrometer scale. During the characterization of perovskite devices or films, it should be remembered that they have a really low damage threshold. When analyzing this family of material, it is necessary to stay at low power density as this will ensure two things: damage will not be caused to the sample, and the experiment can be performed in realistic conditions of solar panels operation.

Characterization of Perovskite Solar Cells with Hyperspectral Global Imaging

Overview of the characterization that can be carried out with hyperspectral global imaging:

• Maps of maximum luminescence intensity give information associated with losses. It is essential that a good solar cell is as luminescent as possible [1], and rapid acquisition of local information on the luminescence offers a better understanding of the device’s overall efficiency.
• It is possible to localize spectral signatures and assign them to grain boundaries, defects, phase segregation, and so on. Luminescence maps can therefore give information on the composition and uniformity of a given solar cell.
• When hyperspectral imaging is combined with a photometric calibration module, local information on the charge transport efficiency, quasi-fermi level splitting, and EQE [2] can also be obtained.

Hyperspectral global electro- and photoluminescence imaging provided important insight on the hybrid perovskite solar cells we are producing in my lab: identification of spatial inhomogeneities lead to a better understanding of the limited fill factors of those devices.

Dr. HENK BOLINK (ICMOL)

Results from Prof. Bolink and the team from EDF R&D and the Institute of Research and Development on Photovoltaic Energy (now the IPVF) are presented here: [2]. Results presented below were acquired during another recent collaboration with Prof. Docampo.

Perovskite crystals—from Dr. Pablo Docampo research group

Figure 1. Monochromatic photoluminescence image extracted at 784 nm

Figure 2. PL spectra extracted from different region of the sample (see corresponding targets)

Figure 3. Map of the PL maximum intensity

References

[1] Miller et al., IEEE J. Photovolt., Vol. 2, No. 3, July 2012, DOI: 10.1109/JPHOTOV.2012.2198434

[2] El-Hajje et al., Energy Environ. Sci., May 2016, DOI: 10.1039/c6ee00462h

This information has been sourced, reviewed and adapted from materials provided by Photon etc.

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