Screen-Printable Contacts for Industrial N-TOPCon Crystalline Silicon Solar Cells

Optimally prepared industrial
n
-type bifacial tunnel oxide passivated contacts c-Si solar cells (156 × 156 mm) fabricated with cost effective screen-printable front-side (FS) and rear-side (RS) silver pastes had a median solar cell efficiency of 22.21% ± 0.10% and bifaciality efficiency factor of 82.9%. A FS paste comprising silver, metallic aluminum, and inorganic frit was designed to contact
p⁺
boron-diffused Si emitter surfaces with SiN
_x
:H–Al
₂
O
₃
antireflection-passivation layers. A RS paste comprising silver and inorganic frit was designed to contact
n⁺
phosphorous-doped surfaces with tunnel-SiO
_x
/
n⁺
poly-Si/SiN
_x
:H layers. The bifacial electrical data indicates efficiency is being limited by the FS contact. The final FS bulk silver metal region microstructure shows isolated metallic aluminum particles surrounded by solidified liquid phase within the bulk sintered silver conductor line. The FS silver metal-
p⁺
boron-diffused emitter contact region shows continuous interfacial (IF) films decorated with silver colloids located between the bulk silver metal and emitter surface. The final RS silver metal-
n⁺
phosphorus diffused contact region again shows continuous IF films between the bulk silver metal and semiconductor surface. A microstructural model suggests electrical contact for both the FS and RS contact regions occurs by a tunneling mechanism though the residual IF films.