Corrosion protection of silver coated reflectors by atomic layer deposited Al2O3

• Evaporated silver films are used for solar concentrators.
• Atomic Layer Deposition was used to apply alumina film on silver films.
• At least 50 nm of alumina is need to provide silver with corrosion protection.
• Failure of the alumina coatings occurs by delamination from the silver film.

Silver is used for the production of the reflective surface of the solar concentrators due to its optical properties and good durability. However, in particular conditions, e.g. when exposed in presence of ozone and pollutants containing sulphur compounds, corrosion attacks might occur. In this work the potential of the Atomic Layer Deposition (ALD) technique to deposit thin and compact ceramic films to shield the silver reflective film against weathering was investigated. Al2O3 films applied onto glass samples coated with a physical vapor deposited silver film were applied by means of Atomic Layer Deposition to increase its durability during outdoor exposure. The effect of a different number of self-terminating gas–surface reactions in the ALD chamber (which lead to different thickness of the deposits) was investigated. The appearance and the physical properties of the coatings were explored by means of FE-SEM observations and ToF-SIMS analyses. The corrosion protection properties of the Al2O3 deposits were investigated by means of electrochemical techniques such as potentiodynamic curves and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of the different samples was characterized. The electrochemical measurements revealed that a ∼80 nm thick Al2O3 deposit is able to decrease up to two orders of magnitude the corrosion current compared to the bare silver substrate.