AUTHOR=Míguez Novoa José Manuel , Hoffmann Volker , Forniés Eduardo , Mendez Laura , Tojeiro Marta , Ruiz Fernando , Funes Manuel , del Cañizo Carlos , Fuertes Marrón David , Dasilva Villanueva Nerea , Caballero Luis Jaime , Arıkan Bülent , Turan Raşit , Canar Hasan Hüseyin , Sánchez Plaza Guillermo TITLE=Production of upgraded metallurgical-grade silicon for a low-cost, high-efficiency, and reliable PV technology JOURNAL=Frontiers in Photonics VOLUME=5 YEAR=2024 URL=https://www.frontiersin.org/journals/photonics/articles/10.3389/fphot.2024.1331030 DOI=10.3389/fphot.2024.1331030 ISSN=2673-6853 ABSTRACT=

Upgraded metallurgical-grade silicon (UMG-Si) has the potential to reduce the cost of photovoltaic (PV) technology and improve its environmental profile. In this contribution, we summarize the extensive work made in the research and development of UMG technology for PV, which has led to the demonstration of UMG-Si as a competitive alternative to polysilicon for the production of high-efficiency multicrystalline solar cells and modules. The tailoring of the processing steps along the complete Ferrosolar’s UMG-Si manufacturing value chain is addressed, commencing with the purification stage that results in a moderately compensated material due to the presence of phosphorous and boron. Gallium is added as a dopant at the crystallization stage to obtain a uniform resistivity profile of ∼1 Ω cm along the ingot height. Defect engineering techniques based on phosphorus diffusion gettering are optimized to improve the bulk electronic quality of UMG-Si wafers. Black silicon texturing, compatible with subsequent gettering and surface passivation, is successfully implemented. Industrial-type aluminum back surface field (Al-BSF) and passivated emitter and rear cell (PERC) solar cells are fabricated, achieving cell efficiencies in the range of those obtained with conventional polysilicon substrates. TOPCon solar cell processing key steps are also tested to further evaluate the potential of the material in advanced device architectures beyond the PERC. Degradation mechanisms related to light exposure and operation temperature are shown to be insignificant in UMG PERC solar cells when a regeneration step is implemented, and PV modules with several years of outdoor operation demonstrated similar performance to reference ones based on poly-Si. Life cycle analysis (LCA) is carried out to evaluate the environmental impact of UMG-based PV technology when compared to poly-Si-based technology, considering different scenarios for both the manufacturing sites and the PV installations.