BiVO4 has become the top-performing semiconductor among photoanodes for photoelectrochemical water oxidation. However, BiVO4 photoanodes are still limited to a fraction of the theoretically possible ...photocurrent at low applied voltages because of modest charge transport properties and a trade-off between light absorption and charge separation efficiencies. Here, we investigate photoanodes composed of thin layers of BiVO4 coated onto Sb-doped SnO2 (Sb:SnO2) nanorod-arrays (Sb:SnO2/BiVO4 NRAs) and demonstrate a high value for the product of light absorption and charge separation efficiencies (ηabs × ηsep) of ∼51% at an applied voltage of 0.6 V versus the reversible hydrogen electrode, as determined by integration of the quantum efficiency over the standard AM 1.5G spectrum. To the best of our knowledge, this is one of the highest ηabs × ηsep efficiencies achieved to date at this voltage for nanowire-core/BiVO4-shell photoanodes. Moreover, although WO3 has recently been extensively studied as a core nanowire material for core/shell BiVO4 photoanodes, the Sb:SnO2/BiVO4 NRAs generate larger photocurrents, especially at low applied voltages. In addition, we present control experiments on planar Sb:SnO2/BiVO4 and WO3/BiVO4 heterojunctions, which indicate that Sb:SnO2 is more favorable as a core material. These results indicate that integration of Sb:SnO2 nanorod cores with other successful strategies such as doping and coating with oxygen evolution catalysts can move the performance of BiVO4 and related semiconductors closer to their theoretical potential.
Bismuth vanadate (BiVO4) is promising for solar‐assisted water splitting. The performance of BiVO4 is limited by charge separation for >70 nm films or by light harvesting for <700 nm films. To ...resolve this mismatch, host–guest architectures use thin film coatings on 3D scaffolds. Recombination, however, is exacerbated at the extended host–guest interface. Underlayers are used to limit this recombination with a host‐underlayer‐guest series. Such underlayers consume precious pore volume where typical SnO2 underlayers are optimized with 65–80 nm. In this study, conformal and ultrathin SnO2 underlayers with low defect density are produced by atomic layer deposition (ALD). This shifts the optimized thickness to just 8 nm with significantly improved space efficiency. The materials chemistry thus determines the dimension optimization. Lastly, host–guest architectures are shown to have an applied bias photon‐to‐charge efficiency of 0.71 %, a new record for a photoanode absorber prepared by ALD.
Underlayer, underlayer, arriba, arriba! The performance of BiVO4 for solar‐assisted water splitting is limited by charge separation for >70 nm films or by light harvesting for <700 nm films. Conformal and ultrathin SnO2 underlayers produced by atomic layer deposition shift the optimized thickness to just 8 nm with significantly improved space efficiency.
The performance of BiVO4 photoanodes, especially under front-side illumination, is limited by the modest charge transport properties of BiVO4. Core/shell nanostructures consisting of BiVO4 coated ...onto a conductive scaffold are a promising route to improving the performance of BiVO4-based photoanodes. Here, we investigate photoanodes composed of thin and uniform layers of BiVO4 particles coated onto Sb-doped SnO2 (Sb:SnO2) nanotube arrays that were synthesized using a sacrificial ZnO template with controllable length and packing density. We demonstrate a new record for the product of light absorption and charge separation efficiencies (ηabs × ηsep) of ∼57.3 and 58.5% under front- and back-side illumination, respectively, at 0.6 V RHE. Moreover, both of these high ηabs × ηsep efficiencies are achieved without any extra treatment or intentional doping in BiVO4. These results indicate that integration of Sb:SnO2 nanotube cores with other successful strategies such as doping and hydrogen treatment can increase the performance of BiVO4 and related semiconductors closer to their theoretical potential.
Abstract
Bismuth vanadate (BiVO
4
) is promising for solar‐assisted water splitting. The performance of BiVO
4
is limited by charge separation for >70 nm films or by light harvesting for <700 nm ...films. To resolve this mismatch, host–guest architectures use thin film coatings on 3D scaffolds. Recombination, however, is exacerbated at the extended host–guest interface. Underlayers are used to limit this recombination with a host‐underlayer‐guest series. Such underlayers consume precious pore volume where typical SnO
2
underlayers are optimized with 65–80 nm. In this study, conformal and ultrathin SnO
2
underlayers with low defect density are produced by atomic layer deposition (ALD). This shifts the optimized thickness to just 8 nm with significantly improved space efficiency. The materials chemistry thus determines the dimension optimization. Lastly, host–guest architectures are shown to have an applied bias photon‐to‐charge efficiency of 0.71 %, a new record for a photoanode absorber prepared by ALD.
The Front Cover shows SnO2 as an effective underlayer for the photoelectrochemical (PEC) water splitting on bismuth vanadate (BiVO4), a promising oxide for water splitting. It is often prepared with ...a host–guest architecture and an underlayer that limits charge recombination at the host–guest interface. Despite widespread use of underlayers relatively little is understood about how the underlayer materials chemistry affects the resulting performance. This is particularly important for host–guest architectures where the short transport paths needed for high PEC efficiency provide a high interfacial area for recombination. To mitigate blocking of pore volume by the interlayer, a very thin SnO2 of only 8 nm (usually 60–80 nm) is prepared by atomic layer deposition, giving rise to improved space efficiency. More information can be found in the Full Paper by B. Lamm et al. on page 1916 in Issue 9, 2019 (DOI: 10.1002/cssc.201802566).
Abstract
Invited for this month′s cover are the Stefik and Rao groups at the University of South Carolina and Worcester Polytechnic Institute. The image shows a fantastical submarine ...solar‐water‐splitting process using the host‐guest architectures described in the report. The Full Paper itself is available at
10.1002/cssc.201802566
.
Invited for this month′s cover are the Stefik and Rao groups at the University of South Carolina and Worcester Polytechnic Institute. The image shows a fantastical submarine solar‐water‐splitting ...process using the host‐guest architectures described in the report. The Full Paper itself is available at 10.1002/cssc.201802566.
“To mitigate blocking of pore volume by the interlayer, a very thin SnO2…” This and more about the story behind the research that inspired the Cover image is presented in the Cover Profile. Read the full text of the corresponding research at 10.1002/cssc.201802566. View the Front Cover here: 10.1002/cssc.201901062.
Metal oxides with moderate band gaps are desired for efficient production of hydrogen from sunlight and water via photoelectrochemical (PEC) water splitting. Here, we report an α-SnWO4 photoanode ...synthesized by hydrothermal conversion of WO3 films that achieves photon to current conversion at wavelengths up to 700 nm (1.78 eV). This photoanode is promising for overall PEC water-splitting because the flat-band potential and voltage of photocurrent onset are more negative than the potential of hydrogen evolution. Furthermore, the photoanode utilizes a large portion of the solar spectrum. However, the photocurrent density reaches only a small fraction of that which is theoretically possible. Density functional theory based thermodynamic and electronic structure calculations were performed to elucidate the nature and impact of defects in α-SnWO4 prepared by this synthetic route, from which hole localization at Sn-at-W antisite defects was determined to be a likely cause for the poor photocurrent. Measurements further showed that the photocurrent decreases over time due to surface oxidation, which was suppressed by improving the kinetics of hole transfer at the semiconductor/electrolyte interface. Alternative synthetic methods and the addition of protective coatings and/or oxygen evolution catalysts are suggested to improve the PEC performance and stability of this promising α-SnWO4 material.
We investigate the impact of grain boundaries and interfaces on dynamics of photoexcited charge carriers in polycrystalline lead sulfide (PbS) films and at interfaces between polycrystalline PbS and ...ZnO by studying transient photoconductivity over sub-picoseconds to microseconds timescales using time-resolved terahertz spectroscopy and time-resolved microwave conductivity measurements. Narrow band gap bulk-like polycrystalline PbS with high absorption in the infrared paired with wide band gap metal oxide current collectors holds promise for infrared photodetectors and photovoltaics for converting infrared radiation to electricity. We find that grain boundaries in polycrystalline PbS suppress long-range conductivity and confine photoexcited carriers within individual crystallites. The mobility of photoexcited holes inside the ∼150 nm crystallites reaches 750 cm2/V s, and their lifetime exceeds hundreds of microseconds, while electrons get rapidly trapped at grain boundary states. The presence of PbS/ZnO interfaces dramatically reduces the lifetime of the photoexcited free holes in the PbS crystallites. Moreover, we detect no injection of free electrons from PbS to ZnO. Optimal transfer of photoexcited electrons, as is needed for optoelectronic devices with PbS/ZnO heterojunctions, may require engineering PbS/ZnO heterojunctions with buffer layers or organic ligands to passivate deleterious interface states.
PDF
