Improved Accuracy of Photoluminescence Images for Quality Control in Solar Cell Production

Photoluminescence (PL) imaging has become an important method for assessing solar cell quality. In practice, laser or camera inhomogeneities can cause a 10-40% PL-intensity variation across the PL-image of a sample, which obscure the valuable PL-information. Using the PL-image of a homogeneous reference sample, the systeminduced inhomogeneities are quantified and corrected for. But as there is no perfect homogeneous reference sample, this reference method introduces new inhomogeneities to the corrected PL-image. In this paper, a method is presented for inline-PL-imaging that can deliver more accurate PL-images without the need for a homogeneous reference sample. In this correction method, a sample needs to be measured twice, with a 90° rotation in-between. The rotation enables the distinction between system imperfections and sample imperfections. A rigorous approach is followed to overlay the two PL-images precisely and merge them into a corrected PL-image. The result can be used as a reference to correct all other PL-images (assuming that the laser was not restarted in-between the measurement). With that procedure, we introduce an effective workaround that helps to strongly improve the representation of sample imperfections in PLimages within a production environment without the need for a homogenization of the illumination.