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

• Reverse bias applied to a-Si solar cells produces an improvement of the performance.
• Sheet resistance improvements is observed in single thin films too.
• Type of bottom contact has a strong influence on the recovery-improvement kinetics.
• Improvement is due to the motion of light ions from the oxide to the a-Si:H films.

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.