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Selective boron emitters using laser-induced forward transfer versus laser doping from borosilicate glass

: Fernandez-Robledo, S.; Kluska, S.; Greulich, J.; Nekarda, J.


IEEE Journal of Photovoltaics 7 (2017), Nr.5, S.1254-1263
ISSN: 2156-3381
ISSN: 2156-3403
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Photovoltaik; Silicium-Photovoltaik; Dotierung und Diffusion

Although highly doped boron selective emitters (SEs) can be formed by using laser doping (LD) from the borosilicate glass remaining after boron tribromide tube diffusion, the dopant concentration is limited. This limitation can be overcome by using a laser-induced forward transfer (DLIFT) approach. In this work, SEs formed by DLIFT and LD are compared to a homogenous tube diffusion (Diff) emitter. We investigated the correlation of the emitter saturation current density (j0e) and the specific contact resistance (ρc) with the sheet resistance (Rsheet) and the laser pulse energy density (Ep,d). For passivated emitters, j0e of DLIFT and LD emitters was around ten times higher than j0e of Diff emitters. For metallized emitters, simulated j0e of DLIFT emitters was lower than j0e of LD and Diff emitters for Rsheet glt; 40.0 Ω/sq. Moreover, we show how j0e can be further reduced by increasing the surface dopant concentration of the boron emitter and by reducing the laser-induced defects in the silicon crystal. Additionally, the metallization of DLIFT emitters with aluminum-silver paste by screen printing provided low contact resistances between metal and silicon (ρc <; 1.0 mΩ · cm2). Thus, p-type emitters can be optimized by forming an SE with the highly doped boron regions achieved by DLIFT under the screen-printed metallization.