We have studied solar water splitting with a composite semiconductor electrode, composed of an n-i-p junction
amorphous silicon (a-Si, Eg≈ 1.7 eV) layer, an indium tin oxide (ITO) layer, and a tungsten trioxide (WO3, Eg 2.8 eV)
particulate layer. The n-i-p a-Si layer, which had more accurately a structure of n-type microcrystalline ( c) 3C-SiC:H
(25 nm)/i-type a-Si:H (400 nm)/p-type a-SiCx:H (25 nm), was prepared on a TiO2-covered F-doped SnO2 (FTO)/glass
plate by a Hot-Wire CVD method. The ITO layer (100 nm thick) was deposited on the p-type a-Si by the DC magnetron
sputtering method, and the WO3 particulate layer was formed by a doctor-blade method, using a colloidal solution of
commercial WO3 powder of 10-30 nm in diameter. The composite electrode thus prepared was finally heat-treated at
300°C for 1 h. The anodic (water oxidation) photocurrent for the composite electrode in 0.1 M Na2SO4 yielded an IPCE
(incident photon to current efficiency) of about 6 % at 400 nm and was stable for more than 24 h. Besides, the onset
potential lay a little (by about 0.05 V) more negative than the equilibrium hydrogen evolution potential, indicating a
possibility of solar water splitting with no external bias. A preliminary result for the water photooxidation with an "n-
GaP/p-Si/Pt dot" electrode is also reported briefly.
A surface alkylated and metal nano-dotted n-Si electrode yields an efficient and stable photovoltaic characteristic in an aqueous redox electrolyte. It generates a high photovoltage due to a unique effect of metal nano-contact and is stabilized by surface alkylation. In the present work, we have prepared a composite electrode, composed of the surface methylated and Pt nano-dotted n-Si single crystal electrode and a tungsten trioxide (WO3) particulate thin film, to decompose water into oxygen and H+ ions under solar irradiation. The onset potential of the oxygen evolution photocurrent for the composite electrode shifts to the negative by about 0.2 V compared with that for the WO3 electrode alone, indicating that the two-step, Z-scheme mechanism operates in the composite electrode, leading to generation of a high photovoltage that comes from a series sum of the photovoltage in the Si and that in the WO3. It is discussed that a composite "polycrystalline Si / visible-light responsive metal-oxide thin-film" electrode is a promising approach to high-efficiency and low-cost solar water splitting.
Conference Committee Involvement (3)
Solar Hydrogen and Nanotechnology III
11 August 2008 | San Diego, California, United States
Solar Hydrogen and Nanotechnology II
27 August 2007 | San Diego, California, United States
Solar Hydrogen and Nanotechnology
14 August 2006 | San Diego, California, United States
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