Simulation Study of Metal-semiconductor Back Contact p-c-Si/Al on Silicon Heterojunction Solar Cells

The silicon HIT (heterojunction with intrinsic thin layer) solar cell has great potential to improve photovoltaic efficiency and reduce costs because of the low temperature deposition technology of hydrogenated amorphous silicon a-Si:H combined with the high stable efficiency of crystalline silicon c-Si. To gain insight into the general functioning of the HIT solar cell, we have studied in this article the semiconductor-metal junction at the back contact of HIT p-type c-Si solar cell: (indium tin oxide (ITO)/hydrogenated n-doped amorphous silicon (n-a-Si:H)/hydrogenated intrinsic polymorphous silicon (i-pm-Si:H)/p-doped crystalline silicon (p-c-Si)/aluminum (Al)). Using computer modeling, we have found that unlike the junction on ITO/ n-a-Si:H on the front HIT solar cells which does not depend on the front contact barrier height b0, an increase in the back contact barrier height bL leads to an upward band bending in the valence band in this type of cell which eliminates the barrier for holes and makes more photogenerated holes able to pass from the active layer (p-doped crystalline silicon p-c-Si) to the metal (aluminium). The increase in the electric field by changing the surface band bending at the junction p-c-Si/Al causes an increase in VOC which leads to an increase in the solar cell efficiency from 17.21 % to 17.38 %. Choosing metal with high work function like palladium, chrome or ruthenium, could be the best choice as a back contact for this type of solar cell.