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Development, characterization and modelling of doping profile, contact resistance, and metal spiking in diffused and screen-printed boron emitters

: Wöhrle, N.; Lohmüller, E.; Werner, S.; Greulich, J.

Fulltext urn:nbn:de:0011-n-3791313 (1.4 MByte PDF)
MD5 Fingerprint: f776ab9ba10cc077f45e2f5bb4c4db68
Created on: 15.3.2016

European Commission:
31st European Photovoltaic Solar Energy Conference and Exhibition, EU PVSEC 2015 : 14 to 18 September 2015, Hamburg, Germany
Hamburg, 2015
ISBN: 3-936338-39-6
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <31, 2015, Hamburg>
Conference Paper, Electronic Publication
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Silicium-Photovoltaik; Pilotherstellung von industrienahen Solarzellen; Messtechnik und Produktionskontrolle; Boron-Emitter; spiking; resistance; profile; crystallites

Opposed to phosphorus n+-emitters on p-type silicon solar cells, p+-emitters on n-type silicon solar cells show altered properties with respect to e.g. dopant diffusion, electrical contacting, and metal induced recombination. This work tries to paint a consistent picture whose results base on deep-penetrating metal spikes (often also referred to as crystallites) formed below Ag-Al screen printing pastes during the contact firing process. By optimizing BBr3 diffusion processes, emitter dark saturation current densities of as low as 30 fA/cm² on alkaline textured and passivated surface are obtained. For considering the interplay between boron doping profile and spike depth regarding the specific contact resistance C, BBr3 diffusion processes are adapted yielding profiles with similar surface concentration but different junction depth. Apart from the maximum boron concentration, the junction depth of the doping profiles impacts C obtained for two examined Ag-Al pastes: deeper junctions lead to lower C. This finding is confirmed by an analytical model taking metal spikes with penetration depths of several 100 nm into account. The known issue of increased recombination below the Ag-Al metallization is addressed by a new simulation approach, which models the actual geometric shape of metal spikes in a three-dimensional (3D) simulation utilizing the quasisteady-state photoconductance (QSSPC) technique. With these 3D QSSPC simulations, we discuss the impact of metal spiking in boron emitters in relation to depth and surface coverage of the spikes, and discuss the scenario which leads to dark saturation current densities of metallized boron emitters in the range of several 1000 fA/cm².