A study on the improvement of amorphous silicon/crystalline silicon heterojunction solar cells by microwave processing

Abstract

The postdeposition microwave heating treatment is carried out on the n-type crystalline silicon with bifacial deposited intrinsic hydrogenated amorphous silicon layers (i/c-Si/i) used as a precursor for amorphous silicon/crystalline silicon heterojunction (SHJ) solar cells. The passivation of i/c-Si/i heterostructure was improved significantly in 5 s microwave processing and two cycles of this processing later it could be stabilized. The results of FTIR show that the hydrogen within (i)a-Si:H layer is released rapidly during the process and the microstructure factor R* continues to decrease versus the processing time. An appropriate amount of hydrogen atoms released from Si–H bonds (especially weak bonds) move to the interface to saturate the dangling bonds favoring the passivation performance but excessive hydrogen release from the layers could lead to extremely poor passivation. The SHJ solar cell with a microwave-treated precursor of i/c-Si/i achieved an improved efficiency of 1.6%_abs corresponding to the reference cell and improved surface passivation quality is the main reason for the efficiency gain, while the efficiency of the cells with the other two microwave-treated precursors of i/c-Si/i/p and n/i/c-Si/i/p increased by 1.1%_abs and decreased by 0.7%_abs, respectively, which may due to the difference in temperature rise during the processing. In addition, the cell with the microwave-treated precursor of i/c-Si/i shows a greater degradation of about 0.4%_abs after storage in the N₂ atmosphere for 312 h, while the cells with the other two precursors show good stability. It indicates that weak bonds formed by dopant atoms with hydrogen may be broken and released during the process, which may play an important facilitator role in the mechanism of degradation after the SHJ solar cells are fabricated.