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Hyperspectral Luminescence Characterization of Multicrystalline Copper-Indium Disulfide cells

Within the second-generation solar cells, copper indium disulfide (CuInS2 or CIS) is one of the most promising materials. It has been under the scope of scientists in the field of photovoltaics since the early 90s, when it already exhibited an efficiency exceeding 10% [1]. Its high absorption coefficient, direct band gap (1.52 eV) [2] and nontoxicity make it an ideal candidate for both thin films and quantum dot-sensitized solar cells. However, CIS efficiency seems to have reached a plateau. To keep improving the next generation of CIS cells and go beyond this limitation, a clear understanding of the impact of the fabrication methods on the cell’s properties is necessary.

a) Integrated PL map of the device, b) PL spectra of selected regions on the studied area. Adapted from [3].
Fig. 1 - a) Integrated PL map of the device, b) PL spectra of selected regions on the studied area. Adapted from [3].

With this in mind, researchers at IPVF (formerly IRDEP - Institute of Research and Development on Photovoltaic Energy) characterized multicrystalline CuInS2 cells using spectrally and spatially resolved photoluminescence (PL) imaging. The hyperspectral platform (IMA) provides a high spectral (< 2 nm) and spatial resolution (~µm). The device is uniformly excited by a 532 nm laser over the whole field of view under the microscope objective. Fig. 1 a) shows the integrated PL map of the device and Fig. 1 b) presents PL spectra of selected regions on the studied area [3]. The global imaging modality provides rapid highlights of spatial inhomogeneity. With this technique, researchers are able to spatially monitor several properties. Indeed, PL maxima offers detailed maps of both the bandgap and the fluctuations of the quasi-Fermi level splitting [4]. With the help of a spectral and photometric absolute calibration module, researchers can extract maps of optoelectronics properties of their devices (e.g.: EQE, Voc, etc.) and improve the fabrication methods.

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[1] Scheer, R., Walter, T., Schock, H. W., Fearheiley, M. L., & Lewerenz, H. J. (1993). CuInS2based thin film solar cell with 10.2% efficiency. Applied Physics Letters, 63(24), 3294–3296.

[2] Suriakarthick, R., Nirmal Kumar, V., Indirajith, R., Shyju, T. S., & Gopalakrishnan, R. (2014). Photochemically deposited and post annealed copper indium disulphide thin films. Superlattices and Microstructures, 75, 667–679.

[3] A. Delamarre, L. Lombez, J.F. Guillemoles, M. Verhaegen, B. Bourgoin. (2011). Characterisation of solar cells using hyperspectral imager, poster presented during PVSEC2011 conference. EDF, IRDEP , CNRS, ParisTech and Photon etc.

[4] Delamarre, A., Paire, M., Guillemoles, J.-F., & Lombez, L. (2014). Quantitative luminescence mapping of Cu(In, Ga)Se2 thin-film solar cells. Progress in Photovoltaics: Research and Applications, 23(10), 1305–1312.

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