EOL thin-film PV modules have been installed in Germany on an ever-increasing scale in recent years. Depending on the different support measures, this boom has already reached most EU member states and led to an increase in installed PV capacity. According to the expectations of the Association of PV Manufacturers (Solar Power Europe), this development will continue in the coming years and reach other economic regions of the world [SOLA-15].
EOL thin-film PV modules have gained importance alongside the classic silicon wafer-based PV module technologies. Their success is due to the high degree of automation in production and the resulting lower purchase price, despite the significantly lower efficiency compared to the classic silicon-wafer-based PV module technologies.
EOL thin-film PV modules consist of light-absorbing semiconductors, which are applied to a glass substrate by chemical bath or vapor phase deposition. In this process, the active metal and semiconductor layers are bonded between two glass plates to form a strong, durable composite. This compact and complex structure directly illustrates the technical challenges that a recycling process for EOL thin-film PV modules faces.
In combination with the expected growth rates, the aspect of module disposal is also coming into focus. There is a lack of market-relevant disposal capacities for silicon wafer-based or EOL thin-film PV modules. EOL thin-film PV modules have so far simply been added to the material flow of the waste glass in diluted doses. The valuable metals are finally lost dissipatively.
The mobilisation of these significant quantities of valuable and increasingly in demand metals for recycling is to be seen as a future challenge for material-flow-specific take-back solutions and recycling technologies in the light of "urban mining". However, the complex structure of EOL thin-film PV modules makes it difficult to separate them into fractions that can be fed into conventional recycling routes.
Due to its innovative process approach, the "PhotoRec" process provides highest selectivity with low process complexity and can thus make a substantial contribution to securing the raw material supply of the solar industry. The long-term goal is to achieve a yield of 90% of semiconductor metals.
The process principle of microwave heating in a vacuum leads to extraordinarily favourable treatment parameters, as the strategic target components remain in the metallic state at low process pressure, low oxygen partial pressure and very high, focused energy density. Furthermore, these process parameters lead to accelerated reaction kinetics, which reflect the economic process potential of short treatment times.
The proposed process thus combines a high resource efficiency with optimized energy efficiency and high productivity potential and, with a high degree of innovation, shows for the first time a solution path how strategic metals can be recovered economically from complex composites even in low concentrations.