Within the second generation solar cells, copper indium disulfide (CuInS2 or CIS) is one of the most promising material. 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% . Its high absorption coefficient, direct band gap (1.52 eV)  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.
With this in mind, researchers at 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 2 nm spectral resolution and a spatial resolution below 2 μm. The device is uniformly excited by a 532 nm laser over the whole field of view under the microscope objective. FIG. 1 shows the integrated PL map of the device and FIG. 2 presents PL spectra of selected regions on the studied area . The global imaging modality provides rapid highlights of spatial inhomogeneities. 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 . With the help of their patented spectral and photometric absolute calibration method (see section below), researchers at IRDEP can extract maps of optoelectronics properties of their devices (e.g. : EQE, Voc, etc.)
While a confocal microscope coupled to a spectrometer could provide similar data, we can show that this alternative time-consuming technique is impractical (FIG. 3). In this case, the 532 nm laser is focused onto the cell front contact and the PL cartography is obtained one point at a time. Comparing the acquisition time of the two methods, global hyperspectral and confocal microscopy, we see that a 150x150 µm² map at 107 W/m² takes only 8 minutes to acquire with the former, but would take hundreds of hours with a confocal microscope .
 Scheer R., Walter T., Schock H. W., Fearheiley M. L., Lewerenz H. J., CuInS2 based thin film solar cell with 10.2% efficiency, Applied Physics Letters, 63, (1993).
 Suriakarthick R. et al., Photochemically deposited and post annealed copper indium disulfide thin films, Superlattices and Microstructures, (2014).
 Delamarre A. et al., Characterisation of solar cells using hyperspectral imager, IRDEP.
 Delamarre A. , Paire M., Guillemoles J.-F. and Lombez L., Quantitative luminescence mapping of Cu(In,Ga)Se2 thin-film solar cells, Progress in Photovoltaics, 10, 1002, (2014).