Optical inspection approach for in-line industrial monitoring of nano and micrometric layers quality in thin film photovoltaics technologies

Photovoltaic (PV) energy will play a key role in Europe’s transition to climate-neutrality by decentralizing and decarbonizing energy production. Currently, the EU funds are concentrated on finding new generations of PV technologies with higher efficiency, lower costs, lower carbon footprint, and high customizability (shape, colour transparency, flexibility, etc.) for ubiquitous integration solutions (building integrated PV, vehicles integrated PV, internet of things, agrivoltaics, etc.). PV technologies based on thin films (TF – like chalcopyrite, perovskite, kesterite) meet all these requirements and are suited to be manufactured with high levels of automation and Industry 4.0 approaches. However, due to the use of multielement materials and multilayer architectures, the manufacturing processes meet various challenges, including the significant impact of each production step on the final product performance. Currently, these steps are barely monitored, making it difficult to detect relevant deviations from the standard processes, due to the absence of in-line compatible methodologies that can be easily integrated and adapted to the customizable products, like TFPV technologies.
In this regard, the current work presents an innovative, fast, non-destructive, easy implementable and adaptable approach for quality control for several properties of different layers at various production steps in TF devices. This approach includes application of spectral and imaging reflectance (%R) and transmittance (%T) spectroscopies to detect deviations from the standard process affecting such critical material parameters as composition, structure and presence of defects, and layer thicknesses. The approach is tested on chalcopyrite, kesterite, and perovskite-based TFPV technologies, including nanometric and micrometric layers used in these technologies. The large-scale (from 10×10 cm2 up to 100×100 cm2) chalcopyrite, perovskites, and kesterite-based solar modules used for the present study were fabricated at industrial or pre-industrial pilot lines of ZSW, Saule, and IREC, respectively. The approach was developed using mainly spectral %R and %T by measuring a statistically relevant number of points (tens per sample). This allowed to select the optimal spectral ranges, and to extend the approach to imaging %R and %T, directly analysing the homogeneity of the respective property of the whole or a representative part of the module by a hyperspectral approach.
The confident results of the spectral and preliminary results of the imaging %R and %T allow to establish this new approach as a fast and non-destructive tool for in-line monitoring of different complex production processes with high accuracy and lateral resolution, as well as to propose this tool for the research community as an option for monitoring their TF baseline processes, with the aim to reduce the material waste, thus to improve the sustainability of both research studies and industrial processes.