Copper indium gallium selenide (CIGS) thin film photovoltaic devices are in the early stages of large-scale commercialization. Their high performance, uniformity, reliability, and a low carbon footprint make them an attractive alternative to standard silicon solar cells. Due to the complex processing required and the associated manufacturing costs, reliable in-line quality control technology is needed. By identifying defective cells early in production, faulty batches can be excluded from further processing, saving resources and costs. We show that micro-Raman spectroscopy (RS) and hyper-spectral imaging (HSI) are powerful tools for quality control and process improvement. Distinctive features in the Raman spectra allow the estimation of the copper to gallium plus indium (CGI) ratio, which is an important criterion for the cell’s efficiency. With HSI in the visible and near infrared range (VNIR) and the near-infrared spectral range (NIR) in combination with machine learning techniques, the layer thickness and CGI ratio are accurately predicted.
Novel thin-film solar cells based on Copper Indium Gallium Selenide (CIGS) are an alternative to standard crystalline silicon cells. This work tests whether two proposed optical methods: Micro-Raman spectroscopy (RS) and photoluminescence (PL) imaging, can measure quality parameters of CIGS PV plates during their manufacture. The investigation followed three steps. Step 1: semi-finished CIGS cells were deposited on a soda-lime glass carrier and measured with Raman and PL. The test cells consisted of a Molybdenum (Mo) back contact, a CIGS layer (varied in the absorber thickness), and a CdS layer. The measurements were used to train models for predictive quality monitoring. Step 2: the plates were finished by adding an iZnO buffer layer, ZnO:Al (AZO) front electrode and divided into 32 cells by scribing down to the Mo layer and electrically tested. I-V parameters such as the open circuit voltage VOC, shunt resistance Rsh, and EQE were measured. Step 3: the finished cells were again measured using the two proposed methods to estimate the composition, efficiency, and VOC of the thin-film cells. Our results show that the proposed methods can non-destructively predict the absorber composition and cell electrical parameters and can therefore be used to exclude samples with poor cell performance at an early production stage.
Copper Indium Gallium Selenide (CIGS) thin-film solar cells are a promising technology, but inline quality inspection systems are required for efficient high-volume production. Tests with two candidate methods: Raman spectroscopy and photo-luminescence imaging, are reported in this paper. The methods were used to estimate material compositions of CIGS samples that were varied in absorber thickness and the composition of the CIGS absorber layer. Our results indicate that both methods can be valuable for contact-free inline inspection during the manufacture of CIGS solar cells, both individually and in combination.
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