Photoluminescence-Based Method for Imaging Buffer Layer Thickness in CIGS Solar Cells

Recent improvements in Cu(In,Ga)Se ₂ (CIGS) solar cells have made use of thinner CdS layers. The homogeneity of this layer is critical to maintain a high-quality CdS/CIGS heterojunction. We present an imaging method based on photoluminescence (PL) intensity ratios using UV and red excitation. UV light is partially absorbed by the CdS, while it is transparent to red photons. Hence, inhomogeneity in the CdS layer thickness produces different UV excitation of the underneath CIGS layer, while the red excitation is uniform, leading to contrast in the PL image ratio. The method is highly sensitive to detect defects or pinholes in the CdS layer and can be used as a rapid method for CdS deposition quality control.