Polycrystalline Silicon Passivating Contacts for High-Efficiency Silicon Solar Cells

Ph D Defense
2022-08-22 14:00
KU Leuven, Universiteitshal, Promotiezaal, 01.46 - Naamsestraat 22
3000 Leuven, België

Promovendus/a: Meriç Firat

Promotor(en): Prof. dr. ir. Jozef Poortmans, Dr. María Recamán Payo

There is a broad scientific consensus that meeting the growing energy demand of the society using fossil fuels is not a viable option to establish a sustainable future. On the contrary, it is necessary to transition to a global energy system based on renewables with net-zero greenhouse gas emissions by 2050, to limit the average global warming to 1.5-2°C and mitigate the adverse effects of climate change. Photovoltaics (PV) is a technology which enables direct conversion of solar energy, the most abundant renewable energy resource, into electricity. While PV has already become the cheapest source of electricity, to facilitate the transition of the global energy system to a sustainable path, the PV market needs to grow rapidly and reach an annual production capacity of ~3 TW by 2050, which is significantly larger than the current capacity of ~0.2 TW per year. This requires reducing the cost of PV devices further, and the most effective strategy for this purpose is to increase the efficiency of the solar cells and modules, without increasing the complexity and cost of manufacturing significantly.

The current mainstream product of the PV industry, the so-called p-PERC silicon solar cell, appears to be reaching its limit, with 24% being foreseen as the maximum achievable efficiency on average in mass production. The upcoming n-TOPCon solar cell technology incorporates a passivating contact, which reduces losses in the efficiency of p-PERC solar cells due to the recombination of electrical charge carriers generated by the absorption of solar energy. As a result, n-TOPCon solar cells yield higher efficiencies than p-PERC, up to 26%. Nevertheless, fabrication of n-TOPCon solar cells require additional process steps compared to p-PERC, leading to similar costs for the two technologies.

In this thesis, two approaches for reducing the complexity and cost of fabricating n-TOPCon solar cells were studied: (i) use of a simplified (in situ) doping process and (ii) omission of a thermal anneal. By the development of the in situ doping process, a leaner fabrication sequence was established for n-TOPCon solar cells. Using this approach, a high efficiency of 23% was demonstrated experimentally, and a roadmap to boost the efficiency to 25.5% by further developments was established. While the omission of the thermal anneal could lead to a further simplified fabrication sequence, highly efficient solar cells could not be demonstrated by this method due to high recombination losses. The underlying reasons for these losses were investigated and paths for potential improvements suggested.

In addition to process simplification, an advanced characterization study of the passivating contacts in n-TOPCon solar cells was undertaken for more accurately describing and modeling such devices. This resulted in the first experimental demonstration of doping non-uniformities adjacent to the passivating contacts, which can improve the understanding of the working principle of n-TOPCon solar cells.

All Dates

  • 2022-08-22 14:00

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