Reverse Bias Behavior of Diffused and Screen-Printed n-Type Cz-Si Solar Cells

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 R P > 30 kΩ · cm 2 (without prior reverse load), while cells with shallower emitters exhibit initial values of R P ≈ 9 kΩ · cm 2 , 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.