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 (C H ) as a-Si:H layers are ultra-thin. High effective carrier lifetime and implied open-circuit voltage (V oc,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 oc,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.

Physical criteria for the interface passivation layer in hydrogenated amorphous/crystalline silicon heterojunction solar cell

“…Hydrogen atoms in the form of monohydride (SiH) were preferred to those in the form of dihydride (SiH2) for the passivation [9]. For an excellent passivation layer, the crystallinity should be lower than 10% [10] and C H should be 5.0-8.5% [11]. Many researchers achieved excellent passivation performance when the passivation layer was deposited just close to the onset of the amorphous-to-crystalline transition phase [12,13].…”