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This article examines some of the basic questions about silicon module recycling: (1) What can be recovered from silicon modules? (2) What recycling technologies are needed? (3) What are the potential revenues for different recycling scenarios? And (4) what are the major challenges for different recycling scenarios? Three recycling scenarios are considered: module reuse, component extraction, and material extraction. Recycling process sequences for different scenarios are outlined. The discussions conclude that module reuse generates the highest revenue with the fewest processing steps, while material extraction leads to the lowest revenue with the most processing steps. It is suggested that gentle and clean separation of silicon solar cells from the glass pane is a critical technology for silicon module recycling. It is also argued that two low‐concentration metals must be recovered from silicon modules: silver as a scarce material and lead as a toxic material. Their recovery requires chemical methods, while bulky materials including glass cullet, aluminum frame, and copper wiring can be recovered with physical methods. The silicon in the cells can be extracted with different qualities: ferro‐silicon, metallurgical‐grade silicon, or solar‐grade silicon, with a higher revenue and more complicated recycling process for purer silicon. Markets outside the solar industry for the recovered silicon should be explored. The biggest challenge for module reuse is to find a large and sustained market for hundreds of gigawatts peak of decommissioned modules a year, and the biggest challenge for component extraction is the many different module and cell structures on the market and cell efficiency variability. For all the three scenarios, the cost of collecting and processing waste modules is a common challenge.

The impact of the transition metals iron, chromium, nickel, titanium and copper on solar‐cell performance is investigated. Each impurity is intentionally added to the silicon feedstock used to grow p‐type, directionally solidified, multicrystalline silicon ingots. A state‐of‐the‐art screen‐print solar‐cell process is applied to this material. Impurities like iron, chromium and titanium cause a reduction in the diffusion length. Nickel does not reduce the diffusion length significantly, but strongly affects the emitter recombination, reducing the solar‐cell performance significantly. Copper has the peculiarity of impacting both base‐bulk recombination as well as emitter recombination. Two models based on the Scheil distribution of impurities are derived to fit the degradation along the ingot. Solar‐cell performances are modelled as a function of base‐bulk recombination and emitter‐bulk recombination. The model fits the experimental data very well and is also successfully validated. Unexpectedly, the distribution of impurities along the ingot, due to segregation phenomena (Scheil distribution), leaves its finger‐print even at the end of the solar‐cell process. A measure of impurity impact is defined as the level of impurity that causes a degradation in cell performance of less than 2% up to 90% of the ingot height. The advantage of this impurity‐impact metric is that it comprises the different impurities’ physical characters in one single parameter, which is easy to compare.

Since June 2003 Deutsche Solar AG is operating a recycling plant for modules with crystalline cells. The aim of the process is to recover the silicon wafers so that they can be reprocessed and integrated in modules again. The aims of the Life Cycle Analysis of the mentioned process are (i) the verification if the process is beneficial regarding environmental aspects, (ii) the comparison to other end-of-life scenarios, (iii) the ability to include the end-of-life phase of modules in future LCA of photovoltaic modules. The results show that the recycling process makes good ecological sense, because the environmental burden during the production phase of reusable components is higher than the burden due to the recycling process. Moreover the Energy Pay Back Time of modules with recycled cells was determined.

The effects of phosphorous gettering and hydrogenation on the minority carrier recombination at crystal defects in directionally solidified multicrystalline silicon are described. Representative industrial wafers, both p- and n-type, and current technologies for the gettering and hydrogenation are used. The main result of this work is a strong link between activation of extended crystal defects (ECDs) by gettering and their passivation by hydrogenation. It is shown that gettering or annealing increases the recombination at active as well as inactive ECDs. Surprisingly, hydrogenation can neutralize this change in activity due to the gettering. However, it neutralizes only part, at most, of the ECD activity already present before the gettering. Therefore, under current industrial processing techniques, these two high-temperature process steps individually give large change but together much less net change of the crystal defect activity. Related phenomena are observed in wafers with strongly varying impurity concentration. Finally, there is little difference in these observations between n- and p-type wafers.