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

Abstract

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 (CH) as a‐Si:H layers are ultra‐thin. High effective carrier lifetime and implied open‐circuit voltage (Voc,im), as well as low surface recombination velocity, were obtained at the appropriate CH values, and the optimal windows of CH and of the hydrogen content in the Si–H2 configuration (C2) were determined to be 5.0 ∼ 8.5 and 2.9 ∼ 6.8 at.%, respectively. For CH values higher than 8.5 at.%, the passivation effect was degraded due to the deteriorated bulk properties of the a‐Si:H layers. However, Voc,im decreased when CH 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.