Raman spectroscopy and photoluminescence imaging for predictive quality monitoring of CIGS solar cells

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.