Enhanced photoelectrochemical effciency and stability using a conformal TiO2 film on a black silicon photoanode

Black silicon (b-Si) is a surface-nanostructured Si with extremely efficient light absorption capability and is therefore of interest for solar energy conversion. However, intense charge recombination and low electrochemical stability limit the use of b-Si in photoelectrochemical solar-fuel production. Here we report that a conformal, ultrathin, amorphous TiO2 film deposited by low-temperature atomic layer deposition (ALD) on top of b-Si can simultaneously address both of these issues. Combined with a Co(OH)(2) thin film as the oxygen evolution catalyst, this b-Si/TiO2/Co(OH)(2) heterostructured photoanode was able to produce a saturated photocurrent density of 32.3mAcm(2) at an external potential of 1.48V versus reversible reference electrode (RHE) in 1M NaOH electrolyte. The enhanced photocurrent relative to planar Si and unprotected b-Si photoelectrodes was attributed to the enhanced charge separation effciency as a result of the effiective passivation of defective sites on the b-Si surface. The 8-nm ALD TiO2 layer extends the operational lifetime of b-Si from less than half an hour to four hours.