M.I.S. solar cells of amorphous silicon on stainless steel, with a top barrier contact of Ni/TiOx, have given 4.8% power conversion efficiency without an antireflection coating. The insulating layer, with an optimum thickness of ≈ 2nm, compensates for the low work function of nickel compared with platinum, and enables similar high open-circuit voltages (up to 680 mV) to be obtained. The fill factor is not appreciably degraded by the addition of an insulating layer, unless this is thicker than = 3 nm. Under illumination, the diode characteristics change compared with their behaviour in the dark; the diode factor, the barrier height, and the series resistance are all dependent on light intensity.