A method of hydrogenation of a silicon photovoltaic junction device is provided, the silicon photovoltaic junction device comprising p-type silicon semiconductor material and n-type silicon semiconductor material forming at least one p-n junction. The method comprises: i) ensuring that any silicon surface phosphorus diffused layers through which hydrogen must diffuse have peak doping concentrations of 1×1020 atoms/cm3 or less and silicon surface boron diffused layers through which hydrogen must diffuse have peak doping concentrations of 1×1019 atoms/cm3 or less; ii) providing one or more hydrogen sources accessible by each surface of the device; and iii) heating the device, or a local region of the device to at least 40° C. while simultaneously illuminating at least some and/or advantageously all of the device with at least one light source whereby the cumulative power of all the incident photons with sufficient energy to generate electron hole pairs within the silicon (in other words photons with energy levels above the bandgap of silicon of 1.12 eV) is at least 20 mW/cm2.