Application of optical hyperspectral imaging for rapid material assessment of perovskite/silicon tandem cells

The development of the perovskite/silicon tandem solar cell technology faces several substantial challenges related to up-scaling of the deposition processes, long-term stability, and inline-capable metrology solutions. The perovskite-related cell layer stacks consist of several additional layers such as hole- and electron transport layers, absorber and transparent conductive contacting layers. This necessitates innovative metrology solutions to assess process and material quality of this complex layer stack. In this work, we demonstrate a new workflow using optical hyperspectral imaging (HSI) to rapidly identify defects and non-uniformities in perovskite/silicon tandem cells. This spatial-optical inspection method requires new ways of analyzing the measurement data due to the vast amount of data collected in one measurement. Here, we present an approach encompassing data acquisition and preprocessing as well as data analysis through classification and clustering of spectral fingerprints. As this approach does not rely on any specific physical model, it is characterized by a universal applicability to a wide range of multilayer stack devices. Specifically, we demonstrate the effectiveness of optical-HSI in characterizing layer inhomogeneities in tandem cells subject to stress testing. We show that there is spatial correlation between HSI-derived classes, LBIC signatures, and locally different Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth-profile responses. The results indicate that HSI provides rapid and non-destructive insights into material characteristics going beyond established imaging techniques, thus enabling improved quality control. This study highlights the potential of optical-HSI as a complementary tool to conventional techniques applied in process control in the photovoltaic industry.