Effect of charge selective contacts on the quasi Fermi level splitting of CuGa<sub>3</sub>Se<sub>5</sub> thin film photocathodes for hydrogen evolution and methylviologen reduction

Yang, Cheng; Xiao, Chengcan; Mahmoudi, Behzad; Scheer, Roland; Maijenburg, A. Wouter; Osterloh, Frank E.

doi:10.1039/d2ey00062h

Cited by 12 publications

(15 citation statements)

References 63 publications

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“…The measurement configuration is shown in Figure S10. We previously showed that the SPV signal generated under these conditions equals the photovoltage V ph of the illuminated FTO/BiVO 4 electrode, 34,35 i.e., the difference of the electrochemical potentials at the front (E F,f ) and back (E F,b ). SPV spectra for a BiVO 4 photoelectrode in contact with the triiodide/iodide electrolyte are depicted in Figure 6a.…”

Section: ■ Results and Discussionmentioning

confidence: 97%

BiVO₄–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

Daemi,

Kaushik,

Das

et al. 2023

J. Am. Chem. Soc.

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BiVO4 is an important photoanode material for water oxidation, but its photoelectrochemistry regarding the triiodide/iodide redox couple is not well understood. Here, we use a combination of open circuit potential measurements, photoelectrochemical scans, and liquid surface photovoltage spectroscopy (SPS) to confirm that BiVO4/triiodide/iodide electrolyte contacts produce up to 0.55 V photovoltage under 23 mW/cm–2 illumination from a 470 nm LED. Inspired by these results, we construct FTO/BiVO4/KI(I2)aq/Pt sandwich photoelectrochemical cells from electrochemically grown 0.5 × 0.5 cm2 BiVO4 and Mo-doped BiVO4 films. Under AM 1.5 illumination, the devices have up to 0.22% energy conversion efficiency, 0.32 V photovoltage, and 1.8 mA cm–2 photocurrent. Based on SPS, hole transfer to iodide is sufficiently fast to prevent the competing water oxidation reaction. Mo doping increases the incident photon-to-current efficiency to up to 55% (at 425 nm under front illumination) by improving the BiVO4 conductivity, but this comes at the expense of a lower photovoltage resulting from recombination at the Mo defects and a detrimental Schottky junction at the interface with FTO. Additional photovoltage losses are caused by the offset between the BiVO4 valence band edge and the triiodide/iodide electrochemical potential and by electron back transfer to iodide at the FTO back contact (shunting). Overall, this work provides the first example of a BiVO4–liquid photovoltaic cell and an analysis of its limitations. Even though the larger band gaps of metal oxides constrain their solar energy conversion efficiency, their transparency to visible light and deep valence bands makes them suitable for tandem photovoltaic devices.

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Section: ■ Results and Discussionmentioning

confidence: 97%

BiVO₄–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

Daemi,

Kaushik,

Das

et al. 2023

J. Am. Chem. Soc.

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“…The advantage of SPS compared to conventional photoelectrochemical characterization techniques is the high sensitivity of the method, since already small charge carrier concentrations (10 10 per cm −2 ) result in potentials on the mV scale [85] . Recently, we have expanded VKP‐SPS to include solid‐liquid interfaces [86] . This is possible by covering the sample with a drop of the electrolyte and a glass cover slip, as shown in Figure 6A.…”

Section: Resultsmentioning

confidence: 99%

Mesoporous CuFe₂O₄ Photoanodes for Solar Water Oxidation: Impact of Surface Morphology on the Photoelectrochemical Properties**

Einert

Waheed

Moritz

et al. 2023

Chemistry A European J

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Metal oxide‐based photoelectrodes for solar water splitting often utilize nanostructures to increase the solid‐liquid interface area. This reduces charge transport distances and increases the photocurrent for materials with short minority charge carrier diffusion lengths. While the merits of nanostructuring are well established, the effect of surface order on the photocurrent and carrier recombination has not yet received much attention in the literature. To evaluate the impact of pore ordering on the photoelectrochemical properties, mesoporous CuFe2O4 (CFO) thin film photoanodes were prepared by dip‐coating and soft‐templating. Here, the pore order and geometry can be controlled by addition of copolymer surfactants poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (Pluronic® F‐127), polyisobutylene‐block‐poly(ethylene oxide) (PIB‐PEO) and poly(ethylene‐co‐butylene)‐block‐poly(ethylene oxide) (Kraton liquid™‐PEO, KLE). The non‐ordered CFO showed the highest photocurrent density of 0.2 mA/cm2 at 1.3 V vs. RHE for sulfite oxidation, but the least photocurrent density for water oxidation. Conversely, the ordered CFO presented the best photoelectrochemical water oxidation performance. These differences can be understood on the basis of the high surface area, which promotes hole transfer to sulfite (a fast hole acceptor), but retards oxidation of water (a slow hole acceptor) due to electron‐hole recombination at the defective surface. This interpretation is confirmed by intensity‐modulated photocurrent (IMPS) and vibrating Kelvin probe surface photovoltage spectroscopy (VKP‐SPS). The lowest surface recombination rate was observed for the ordered KLE‐based mesoporous CFO, which retains spherical pore shapes at the surface resulting in fewer surface defects. Overall, this work shows that the photoelectrochemical energy conversion efficiency of copper ferrite thin films is not just controlled by the surface area, but also by surface order.

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“…These experiments were conducted using the contact potential difference (CPD) method in air to initially eliminate the complexity of the solid/liquid interface and to independently compare results to the PEC characteristics. Such measurements have been used extensively for probing buried photovoltaic junctions, − as well as for determining the quasi-Fermi level splitting in semiconductor photoelectrode materials. , As shown in Figure , for the case of InP/TiO x heterostructures, remarkable differences between the shapes and magnitudes of intensity-dependent SPV from TTIP/H 2 O and TDMAT/H 2 O samples are observed. In particular, the TDMAT/H 2 O sample exhibits an S-like dependence of SPV as a function of light intensity, with the onset of photovoltage only occurring at higher light intensities.…”

Section: Resultsmentioning

confidence: 99%

Engineering Defects and Interfaces of Atomic Layer-Deposited TiO_x-Protective Coatings for Efficient III–V Semiconductor Photocathodes

Bienek,

Fuchs,

Kuhl

et al. 2023

ACS Photonics

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III–V compound semiconductors offer optoelectronic properties that are well suited for the conversion of solar energy to chemical fuels. While such materials suffer from poor stability under photoelectrochemical (PEC) conditions, atomic layer deposition (ALD) of titanium oxide (TiO x ) has emerged as a powerful approach for creating corrosion protection layers, thereby enabling efficient and robust interfaces. However, the role of defects within TiO x layers and at the semiconductor/TiO x interface on the PEC performance remains poorly understood and controlled. Here, we use p-type InP as a model III–V semiconductor to investigate the impact of defects in ALD TiO x on junction formation, interfacial charge transport, and photocarrier recombination, which underpin characteristics of PEC devices. We show that defect concentrations in TiO x can be tuned over a broad range, resulting in significant modulation of the optical constants, electrical conductivity, and interface chemistry. While plasma-enhanced ALD yields films with low midgap-state concentrations, it introduces series resistance losses due to oxidation of the substrate. In contrast, thermal ALD suppresses interface oxidation but leads to electronically active defect states within the band gap of TiO x . By controlling these defect states, the nature of junction formation can be tuned, and high photovoltage photocathodes can be achieved. In particular, ALD TiO x layers possessing high carrier concentrations form buried InP/TiO x pn heterojunctions, whereas less defective layers preserve semiconductor/electrolyte junction energetics to achieve large photovoltages and applied bias photon-to-current efficiencies. These results highlight the power of ALD for engineering photoelectrode interfaces and provide a new route for tailoring the junction formation between buried and PEC junctions.

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Effect of charge selective contacts on the quasi Fermi level splitting of CuGa₃Se₅ thin film photocathodes for hydrogen evolution and methylviologen reduction

Abstract: The defect-copper chalcopyrite CuGa3Se5 is a promising photocathode material for solar hydrogen generation. Here we assess its performance with photoelectrochemical measurements and vibrating Kelvin probe surface photovoltage spectroscopy.

Cited by 12 publications

References 63 publications

BiVO₄–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

BiVO₄–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

Mesoporous CuFe₂O₄ Photoanodes for Solar Water Oxidation: Impact of Surface Morphology on the Photoelectrochemical Properties**

Engineering Defects and Interfaces of Atomic Layer-Deposited TiO_x-Protective Coatings for Efficient III–V Semiconductor Photocathodes

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Effect of charge selective contacts on the quasi Fermi level splitting of CuGa3Se5 thin film photocathodes for hydrogen evolution and methylviologen reduction

Abstract: The defect-copper chalcopyrite CuGa3Se5 is a promising photocathode material for solar hydrogen generation. Here we assess its performance with photoelectrochemical measurements and vibrating Kelvin probe surface photovoltage spectroscopy.

Cited by 12 publications

References 63 publications

BiVO4–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

BiVO4–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

Mesoporous CuFe2O4 Photoanodes for Solar Water Oxidation: Impact of Surface Morphology on the Photoelectrochemical Properties**

Engineering Defects and Interfaces of Atomic Layer-Deposited TiOx-Protective Coatings for Efficient III–V Semiconductor Photocathodes

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Effect of charge selective contacts on the quasi Fermi level splitting of CuGa₃Se₅ thin film photocathodes for hydrogen evolution and methylviologen reduction

BiVO₄–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

BiVO₄–Liquid Junction Photovoltaic Cell with 0.2% Solar Energy Conversion Efficiency

Mesoporous CuFe₂O₄ Photoanodes for Solar Water Oxidation: Impact of Surface Morphology on the Photoelectrochemical Properties**

Engineering Defects and Interfaces of Atomic Layer-Deposited TiO_x-Protective Coatings for Efficient III–V Semiconductor Photocathodes