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Characterization of POCl3-based codiffusion processes for bifacial N-type solar cells

: Rothhardt, P.; Meier, S.; Maier, S.; Jiang, K.Y.; Wolf, A.; Biro, D.


IEEE Journal of Photovoltaics 4 (2014), No.3, pp.827-833
ISSN: 2156-3381
ISSN: 2156-3403
Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit BMUB
0325491; THESSO
Journal Article
Fraunhofer ISE ()

Bifacial n-type silicon solar cells typically feature two highly doped areas, namely, a boron-doped emitter and phosphorus-doped back-surface field (BSF). Complexity of the process sequence for forming these highly doped areas is one of the major obstacles for industrial application. This study investigates a POCl3-based codiffusion process that allows for forming boron-doped emitter and phosphorus-doped BSF in one single high-temperature step. As a boron source, we use a borosilicateglass (BSG) layer deposited before the diffusion process using atmospheric pressure chemical vapor deposition. We discuss the influence of the POCl3 concentration in the process atmosphere with respect to recombination and contact formation of the BSF. By tuning the POCl3 concentration, we achieve specific contact resistances of screen printed contacts below 5 m and dark saturation current densities below 160 fA/cm(2) on a textured surface. We present solar cell results on 156-mm n-type Cz wafers with peak efficiencies of 19.6%.