The integration of light-absorbers with functional catalysts is one of the primary challenges in the area of Solar Fuels research. In this work, we report progress in improving the band-edge properties of p-Si(111) photocathodes for the goal of dihydrogen (H2) production. While silicon possesses a nearly ideal band-gap [Eg = 1.1 eV] for the H2 half-reaction of water-splitting, the band-edge of methylated p-Si(111)-CH3 surfaces is far too negative due to the δ+ dipole effect (and corresponding low p-type barrier height) of the Si-CH3 unit. Here, we find that exchange of Si-CH3 for other alkyl or aryl reagents modulates the band-edge by 250-350 mV, improving the operating potential of p-Si(111)-R|Pt devices closer to the H+/H2 standard potential. Secondly, the identity of the metal oxide protection layer (Al2O3 or TiO2) also modulates the observed band-edge. Taken in summary, this synergistic, hybrid molecular / materials (HMM) approach leads to p-Si(111)|R|MO|Pt photocathodes that operate well positive of NHE under 1-sun illumination. The significant effects of the Pt overlayer on electron transport (ET) through varying film thicknesses (5-200 Å) will also be highlighted. The implications for deriving 'wireless' solar water-splitting devices will be discussed.

Hybrid molecular/materials passivation of p-silicon(111) photocathodes: Band-edge modulation with organic surface linkers and thin film Al2O3 or TiO2

249th National Meeting (2015)

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