Role of electric field and electrode material on the improvement of the ageing effects in hydrogenated amorphous silicon solar cells

The effects of prolonged exposure to reverse bias DC electric fields and illumination as a function of temperature in hydrogenated amorphous Si (a-Si:H) photovoltaic p-i-n cells have been investigated. These are strongly affected by the well known Staebler-Wronski effect, occurring during light soaking of a-Si:H photovoltaic cells. In this work we show that the application of a reverse bias stress in presence of illumination not only slows down the solar cell ageing kinetics but even produces an improvement of the cells parameters as a function of stress time. We discuss the effect of temperature, electric field intensity and illumination level. We also show that different types of bottom contact over which the a-Si:H is grown by PECVD have a strong influence on the recovery-improvement kinetics: SnO:F (FTO) transparent conductive oxide (TCO) and molybdenum bottom contacts to the p-type a-Si:H layer are here compared. Finally, we demonstrate that an analogous improvement (reduction) of sheet resistance is observed in single thin films of doped a-Si:H deposited on SiO2 under the application of high intensity electric fields.