PhotoRec

EOL thin-film PV modules have been installed on an ever-increasing scale in Germany in recent years. Depending on the various support measures, this boom has already spread to most EU member states and led to an increase in installed PV output. 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].

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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 classic silicon wafer-based PV module technologies.

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EOL thin-film PV modules consist of light-absorbing semiconductors that are applied to a glass substrate by chemical bath or vapor phase deposition. The active metal and semiconductor layers are bonded between two glass plates to form a solid, durable composite. This compact and complex structure directly illustrates the technical challenges facing a recycling process for EOL thin-film PV modules.

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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. To date, EOL thin-film PV modules have simply been added to the waste glass material flow in diluted doses. The valuable metals are ultimately lost through dissipation.

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The mobilization of these significant quantities of valuable and increasingly sought-after metals for material 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.

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Thanks to its innovative process approach, the "PhotoRec" process achieves maximum selectivity with low process complexity and can therefore make a substantial contribution to securing the supply of raw materials for the solar industry. In the long term, the aim is to achieve a yield of 90% of semiconductor metals.

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The process principle of microwave heating in a vacuum leads to extraordinarily favorable 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. In addition, these process parameters lead to accelerated reaction kinetics, which reflect the economic process potential of short treatment times.

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The proposed process thus combines high resource efficiency with optimized energy efficiency and high productivity potential and, with a high degree of innovation, is the first to demonstrate a solution for recovering strategic metals from complex composite materials in an economical way, even in low concentrations.