Advanced Photoluminescence Imaging Method for Robust and Scalable Perovskite Quality Monitoring in Monolithic Tandem Solar Cells

Photoluminescence-based characterization techniques are widely employed in perovskite solar cell research, offering a noninvasive and contactless means of obtaining information about the implied open-circuit voltage ( $i{V}_{\mathrm{oc}}$) and, hence, the absorber quality. Driven by the idea of developing a robust yet quantitative in-line imaging method for perovskite/Si tandem solar cells, we have extended an intensity-dependent photoluminescence method initially reported for single-junction solar cells. This method enables local quality assessment of the perovskite thin-film absorbers processed over planar and textured silicon bottom solar cells with high spatial resolution. A single effective parameter k, also called optical ideality factor, is extracted, which accounts for the complex superposition of locally competing recombination processes. This work demonstrates that our method, called k-imaging, is a robust and versatile characterization tool for perovskite/Si tandem solar cells that allows the assessment of the general thin-film absorber quality as well as of specific defects for both scientific and industrial applications. Consequently, it accelerates perovskite research and paves the way for highly reproducible perovskite deposition processes toward commercialized perovskite/Si tandem solar cells.