Abstract
Phosphonic acid multi-layers are used to tune the band alignment in heterojunction devices used for photoelectrochemistry and photovoltaics.
Highlights
Stable and tunable phosphonic acid dipole layer for band edge engineering of photoelectrochemical and photovoltaic heterojunction devices†
After assessing several oxide materials (Fig. S1 and S2, Electronic supplementary information (ESI)†), we found that Al2O3 performed best as anchoring layer and is straight-forward to deposit homogeneously in well-defined thicknesses by atomic layer deposition (ALD)
We have shown that inorganic, molecular phosphonic acid layers can be used as interface dipole layers to increase the photovoltage of several heterojunctions employed for photoelectrochemical (PEC) water splitting
Summary
Stable and tunable phosphonic acid dipole layer for band edge engineering of photoelectrochemical and photovoltaic heterojunction devices†. A key challenge for photoelectrochemical water splitting is that high performance semiconductors are not stable in aqueous electrolytes, necessitating corrosion protection layers such as TiO2. The bands of most high performance semiconductors are poorly aligned with TiO2, limiting the photovoltage. We describe a method to overcome this limitation through the placement of a tunable dipole layer at the interface of the p- and n-type materials, shifting the relative band positions to enable an increased photovoltage. The introduction of a phosphonic acid (PA, H3PO3) layer increases the photovoltage of TiO2-protected Si, Sb2Se3, and Cu2O photocathodes. The dipole effect scales with PA surface coverage, and gives even larger shifts when multilayers are employed. By varying the thickness from submonolayer to multilayer (up to 2 nm), we are able to tune the photovoltage of p-Si/TiO2 over a range of 400 mV
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