The improvement of tandem hydrogenated amorphous/microcrystalline Si solar cells under prolonged exposure to reverse bias direct current electric fields and illumination has been investigated. In this work, the authors show that the application of reverse bias stress in the presence of illumination slows down the solar cell ageing kinetics (caused mainly by the Staebler–Wronski effect and by the increase in the series resistance) and, in suitable conditions, it produces an improvement of the solar cell characteristic parameters as a function of stress time. The authors discuss the effect of temperature, electric field intensity, and illumination level.