Study of the correlation between hydrogenated amorphous silicon microstructure and crystalline silicon surface passivation in heterojunction solar cells

摘要

The properties of hydrogenated amorphous silicon (a-Si:H) thin layers were studied by spectroscopic ellipsometry (SE) and Fourier transform infrared spectroscopy (FTIR) measurements to determine their effects on the surface passivation of crystalline silicon (c-Si) in heterojunction solar cells. It was demonstrated that the high bulk quality of a-Si:H layers with denser structures was not sufficient for the passivation of c-Si surfaces in Silicon Heterojunction (SHJ) solar cells, in which the passivation performance is strongly governed by the total hydrogen content (C_H) as a-Si:H layers are ultra-thin. High effective carrier lifetime and implied open-circuit voltage (V_(∝,im)), as well as low surface recombination velocity, were obtained at the appropriate C_H values, and the optimal windows of C_H and of the hydrogen content in the Si-H_2 configuration (C_2) were determined to be 5.0 ～ 8.5 and 2.9 ～ 6.8 at.%, respectively. For C_H values higher than 8.5 at.%, the passivation effect was degraded due to the deteriorated bulk properties of the a-Si:H layers. However, V_(∝,im) decreased when C_H was lower than 5.0 at.% because the number of H atoms was insufficient to saturate the dangling bonds at the a-Si: H/c-Si interface even though the a-Si:H layers had dense microstructures.