Electrochemical Stability of n-Si Photoanodes Protected by TiO2 Thin Layers Grown by Atomic Layer Deposition

Abstract

This work investigates the n-Si photoanodes corrosion protection by Atomic Layer Deposition (ALD) of a TiO2 film. A specific electrochemical experimental sequence (including successive rest potential measurements and voltammetries under illumination or not) has been established to study the stability of the electrodes in KOH. Depending on the deposition conditions (precursor composition and temperature), the electrochemical properties of the layers are different. The photoanodes coated using titanium tetraisopropoxide (TTIP) at low temperature exhibit a low photocurrent (j ph) that is progressively enhanced during the electrochemical sequence and their stability decreases. When using tetrakis(dimethylamido)titanium (TDMAT), the j ph is almost constant and the film prevents from corrosion. The characterizations show that the ALD parameters drive the microstructure of the layer that is found critical for the electrochemical response. A hydrogen doping occurring during the open circuit potential measurements under illumination is evidenced by IR spectroscopy. It is mainly localized at the grain boundaries and pores of the layers as well as in the n-Si and it modifies the charge transfer at the electrode/solution junction and the hydrogen diffusion weakens the film causing the Si corrosion. The different charge transfer mechanisms are finally proposed depending on the ALD conditions and the film thickness.