An worldwide crew of researchers has proposed a sequence of processes to recuperate silicon and different metals from recycled photo voltaic cells. Their objective is to reuse the recovered silicon within the PV provide chain.
A European group of scientists is investigating the technical feasibility of bodily restoration of metallic contacts from photo voltaic cells faraway from end-of-life photo voltaic panels and the qualification of recovered silicon to be used this once more within the PV provide chain.
“This actuality urgently requires the design and adoption of low-cost, efficient, and a number of methods to recycle and reuse all PV elements, and particularly those who require extra power of their make and due to this fact chargeable for the best environmental impression quote. : the photo voltaic cells,” defined the scientists.
Demetalization
For metallic contact restoration, the group used potassium hydroxide (KOH)-ethanol-water options to optimize the demetallization course of. It examined completely different answer configurations of outdated monocrystalline photo voltaic cells. The entrance contacts of the cells are made with silver screen-printing paste, in addition to the again contacts, though in addition they have traces of different metals, resembling aluminum, iron, or lead.
“The working situations for every experiment had been as follows: 105 min immersion in 250 mL of etching answer, with a strong/liquid ratio of 0.004 g/mL, magnetic stirring, and temperature from 60 C to 70 C ,” the scientists mentioned. Pre- and post-treatments are carried out to reduce the presence of impurities on the floor of the pattern.
The demetallization experiments had three variables – completely different working temperatures (60 C, 65 C, and 70 C), completely different parts of KOH (10%, 15%, and 20%), and completely different charges of ethanol (5%, 10%, and 15). %). The course of is carried out in a 250 mL tall beaker the place the cell fragments are launched in a vertical place held by plastic forceps.
“The design of the experiments permits to conclude that the temperature is probably the most influential parameter of the burden loss and the demetallization charge, whereas the ethanol-temperature interplay is probably the most influential issue of the minority provider lifetime,” they mentioned. “Processing at a temperature of 60 C in a ten% KOH – 5% ethanol answer for 105 min was discovered to be the most suitable choice for recovering pure metals whereas preserving as a lot silicon as doable.”
Recrystallization
Regarding the method of recrystallizing the recovered silicon, the tutorial began with “cleaned fragments of outdated B-doped multicrystalline industrial wafers”, manufactured within the 2000’s. They use a Czochralski (Cz) grower to supply an ingot, which is sliced into 79 wafers. It goes by way of phosphorous diffusion gettering (PDG) processes, to enhance their transport properties.
“After the profitable progress and slicing of the wafers, a full optoelectronic characterization program was carried out,” mentioned the analysis group. “It reveals the achievement of the essential necessities to make new photo voltaic cells, when it comes to wafer resistivity (about 1 Ω cm), oxygen content material (about 1,018 cm3), mobility (about 1,000 cm2 / V⋅s ), and provider lifetimes (exceeding the 100 μs threshold in all instances and reaching a most worth of 350 μs).”
The crew used the recovered supplies to make phosphorus/aluminum again floor discipline (P/Al-BSF) photo voltaic cells. The construction consists of evaporated metallic contacts, with titanium/palladium/silver (Ti/Pd/Ag) for the entrance contact and Al for the again. Finally, the IV traits had been obtained underneath at some point of sunshine in 4 cells and in contrast with a reference.
“From our outcomes, we conclude that the principle gadget efficiency limitations noticed in units made out of recrystallized materials and demetallized wafer fragments will not be because of the degradation of the fabric high quality on the finish suffered through the restoration and use levels of silicon substrates however pitfalls throughout cell manufacturing,” the crew concluded.
Its evaluation is introduced within the paper “Validation of recycling processes for demetallization and recrystallization of silicon photo voltaic cells,” revealed in Solar Energy. The analysis was carried out by scientists from Complutense University of Madrid in Spain, Polytechnic University of Madrid, and Leibniz Institute for Crystal Growth (IKZ) in Germany.
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