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Advanced BBr3 diffusion with second deposition step for selective emitter formation by laser doping

: Lohmüller, S.; Lohmüller, E.


Physica status solidi. Rapid research letters 12 (2018), No.7, Art. 1700442
ISSN: 1862-6254
ISSN: 1862-6270
Journal Article
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Photovoltaik; Silicium-Photovoltaik; Dotierung und Diffusion; Pilotherstellung von industrienahen Solarzellen; doping; diffusion; glass; BSG; doping

The concept of attaching a second deposition step at the end of boron tribromide (BBr3) diffusion is introduced, where second deposition describes an active ni­tro­gen flow through the BBr3 bubbler. This approach pro­vides a high­er boron dose in the borosilicate glass (BSG) which facilitates the formation of laser‐doped se­lec­tive emitters. It is found that the second deposition hardly impacts the as‐diffused charge carrier con­cen­tra­tion profile in comparison to BBr3 dif­fu­sion without second deposition. The emitter sheet re­sis­tance Rsh ≈ 110 Ω sq−1 and emitter dark saturation cur­rent den­si­ty j0e ≈ 25 fA cm−2 (alkaline textured, Al2O3/SiNX passi­va­tion) are similar for both processes. The BBr3 diffusion process forms a BSG/silicon dioxide (SiO2) stack layer on the silicon. The BBr3 diffusion with second deposition step results in an 8 nm thicker BSG/SiO2 stack layer (total thickness: 42 nm) with fac­tor two higher boron dose compared to the BBr3 diffusion without second deposition. After laser doping, the charge carrier concentration is higher for the BBr3 pro­cess with second deposition resulting in stronger local doping with about 10 Ω sq−1 lower Rsh. For laser‐doped and Al2O3/SiNX‐passivated areas, a promising process combination results in j0e = (250 ± 30) fA cm−2 at Rsh = (65 ± 1) Ω sq−1.