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

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 mu s). 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 O-2 pulse or a N-2-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 N-2-plasma deposited Pt nanoparticles coated by ultra-thin SiO2 film show an enhanced stability (85 h-4 days/night cycles).