ALD Pt nanoparticles and thin-film coatings enhancing the stability and performance of silicon photocathodes for solar water splitting

Abstract

We report on thin-film coatings and catalyst nanoparticles both deposited by atomic layer deposition (ALD) on silicon (Si) photocathodes that simultaneously enhance their performance and stability. Regarding thin-film coatings, we scan various materials (SiO₂, TiO₂ and Al₂O₃) appropriate for the electrical passivation of Si surface defects, which result in high minority carrier lifetimes (up to 100 μs). However, these passivating layers seem to act as a barrier for the photogenerated carriers obstructing them from participating in the hydrogen evolution reaction, thus limiting the onset potential (V_on). Regarding platinum (Pt) nanoparticles, two deposition approaches are followed based on using different co-reactants during the ALD process, i.e. an O₂ pulse or a N₂-plasma pulse, with the latter resulting in a higher V_on (505 mV). By combining thin-film SiO₂ coatings of various thicknesses deposited on top of ALD Pt nanoparticles, a synergetic effect of performance and stability enhancement is observed, with V_on values reaching 525 mV. Finally, by systematically studying the Si photocathodes in a day/night cycle operation and using the case of electroless deposited Pt nanoparticles as a benchmark, the N₂-plasma deposited Pt nanoparticles coated by ultra-thin SiO₂ film show an enhanced stability (85 h-4 days/night cycles).