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Reverse bias behavior of diffused and screen-printed n-type Cz-Si solar cells

: Lohmüller, E.; Fertig, F.; Werner, S.; Geisemeyer, I.; Clement, F.; Biro, D.


IEEE Journal of Photovoltaics 4 (2014), No.6, pp.1483-1490
ISSN: 2156-3381
Journal Article
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Silicium-Photovoltaik; Pilotherstellung von industrienahen Solarzellen; cells; pattern; current; Emitter; depth

In this study, we investigate current flow in reverse bias mode and its impact on conversion efficiency for large-area n-type Cz-Si H-pattern and n-type Cz-Si metal wrap through (MWT) solar cells. Shunting is studied as a function of the boron emitter doping profile and by comparing MWT cells with two different phosphorus-doped back surface field (BSF) structures. Less shunting is observed for cells with deeper boron-doped emitters (depth d ≈ 700 nm) compared with cells with shallower emitters (d ≈ 500 nm). Cells with a deeper doping profile have initial shunt resistances of RP > 30 kΩ · cm2 (without prior reverse load), while cells with shallower emitters exhibit initial values of RP ≈ 9 kΩ · cm2, irrespective of the cell type. Furthermore, cells with deeper boron doping profiles show significantly lower current flows under reverse bias. We observe a halving of the RP-values after reverse biasing the H-pattern and the MWT cells with structured BSF where, on the other hand, the conversion efficiencies are hardly affected. MWT cells featuring a BSF below the external p-type contacts show a drop in conversion efficiency of 0.3%abs. This is due to degradation of the electrical insulation between via paste and BSF after reverse bias stress.