A passivating contact for silicon solar cells formed during a single firing thermal annealing

• Published in: Nature energy Vol. 3; no. 9; pp. 800 - 808
• Main Authors: Ingenito, Andrea, Nogay, Gizem, Jeangros, Quentin, Rucavado, Esteban, Allebé, Christophe, Eswara, Santhana, Valle, Nathalie, Wirtz, Tom, Horzel, Jörg, Koida, Takashi, Morales-Masis, Monica, Despeisse, Matthieu, Haug, Franz-Josef, Löper, Philipp, Ballif, Christophe
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2018; Nature Publishing Group
• Subjects: 639/301; 639/4077; 639/4077/909/4101/4096/946; Annealing; Boron; Carbon content; Crystallization; Current carriers; Economics and Management; Electric contacts; Electrical properties; Energy; Energy conversion efficiency; Energy Policy; Energy Storage; Energy Systems; High temperature; Open circuit voltage; Photovoltaic cells; Renewable and Green Energy; Silicon; Solar cells; Temperature requirements; Thin films
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/s41560-018-0239-4

Passivating contacts are indispensable for achieving high conversion efficiency in crystalline-silicon solar cells. Their realization and integration into a convenient process flow have become crucial research objectives. Here, we report an alternative passivating contact that is formed in a single post-deposition annealing step called ‘firing’, an essential step for current solar cell manufacturing. As firing is a fast (<10 s) and high-temperature (>750 °C) anneal, the required microstructural and electrical properties of the passivating contact are stringent. We demonstrate that tuning the carbon content of boron-doped silicon-based thin films inhibits firing-induced layer delamination without preventing a partial crystallization. The latter promotes charge-carrier selectivity, even in the absence of a diffused doped region beyond the oxide, by inducing hole accumulation near the wafer surface. We fabricated proof-of-concept solar cells employing the developed technology, demonstrating an open circuit voltage of 698 mV and an efficiency of 21.9%, and show how it could be a drop-in replacement for today’s rear contacts based on locally opened dielectric passivation stacks. To minimize recombination losses and therefore increase the conversion efficiency of crystalline silicon solar cells, researchers have relied on passivating contacts. Here, the authors demonstrate a hole-selective passivating contact that exploits the firing step currently employed in industrial manufacturing.