A hydrogen-plasma treatment has been used for the first time to fabricate wide-gap, high-quality a-Si:H films. The hydrogen content (CH) of a-Si:H films substantially increases by the hydrogen-plasma treatment after deposition, without deteriorating the opto-electric properties of the films. The photoconductivity (σph) of ≥ 10-5 ο-1 cm-1, photosensitivity ( σ ph/σ d) of > 106 and SiH2/SiH of <0.2 are achieved for a film with CH of ∼25 atomic >%. The optical gap of the film is > 1.70 eV by the (α h ν )1/3 plot, and is >2 eV by the Tauc's plot. The open circuit voltage of a-Si solar cells exceeds 1 V conserving the fill factor of > 0.7 when the wide-gap a∼Si:H films are used as the i-layer, which proves the wide band gap and low defect density.