Investigation of the interface defect density at pm-Si:H/c-Si and the surface recombination speeds on silicon heterojunction solar cells

Abstract

We carefully analyze in this article, the influence of the interface defect density of the defective surface between crystalline silicon and hydrogenated polymorphous silicon (i-pm-Si:H/n-c-Si) on the current density-voltage (J–V) characteristic of n-type HIT solar cells (ITO/p-a-SiC:H/i-pm-Si:H/n-c-Si/Al). We have also studied the variation of the electrons and holes surface recombination speeds on the front and the back face of the studied cell. The results show that the recombination rate is higher on the front surface of the c-Si wafer when the defect density increases. Indeed, we have found that for the two values of the front contact barrier height at the ITO/p-a-SiC:H, when the interface defect density increases, the Voc and the FF drop. Thus, the efficiency goes from almost 20 to 2 %. These results allow us to conclude that to have a good Voc, the surface of the active layer should be passivated to have a interface defect density less than 1011 cm−2. For the variation of the surface recombination speed SnL with the interface defect density for electrons at the back face of the solar cell, no sensitivity is observed. For small values of these defects, the efficiency increases when the holes surface recombination speed SpL is decreased, but for large values of interface defect density, no improvement is observed, even for low surface recombination speeds.