We investigate the influence of argon plasma assistance on the depletion of SiH4 in the preparation of pc-Si:H films via plasma-enhanced chemical vapor deposition (PECVD). From optical emission spectrometry (OES) data of the pc-Si:H deposition, we infer that the excited Ar+ and metastable Ar+ states enhance the dissociation of SiH4 and H-2 molecules to generate ultra-depletion of SiH4. The ultra-depletion of SiH4 increases the lsc-Si:H thinfilm deposition rate from 4.5 A/s to 23.4 angstrom/s at 6-sccm flow of SiH4. This ultra-depletion condition facilitates the gradual substitution of H-2 by Ar, which leads to reduced crystallinity at low argon fractions (far), preferential crystallographic orientation along the (111) direction, and fluctuation of the hydrogen content and microstructure factor (R). Thus, the properties of the pc-Si:H thin films can be controlled via control of the atomic hydrogen generation and physical sputtering effects. The highest photosensitivity (2.2 x 10(3)) is observed at far = 56%. Furthermore, we fabricate an a-Si:H/pc-Si:H tandem solar cell with a total thickness of 1450 nm. The cell exhibits an initial efficiency of 11.44%, and the efficiency reduces to 10.24% after 1000 h of light soaking. The cell also exhibits a significantly higher V-oc x FF stability over that of J(SC).