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 32.3 mA cm^-2 at an external potential of 1.48 V versus reversible reference electrode (RHE) in 1 M NaOH electrolyte. The enhanced photocurrent relative to planar Si and unprotected b-Si photoelectrodes was attributed to the enhanced charge separation efficiency as a result of the effective 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.

Nature Energy 2, Article number: 17045 (2017)
doi:10.1038/nenergy.2017.45

http://www.nature.com/articles/nenergy201745