Electric Fields Control TiO2(e(-)) + I3(-) → Charge Recombination in Dye-Sensitized Solar Cells.

The journal of physical chemistry letters · 2014 · Unclear · Insufficient evidence

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UnclearInsufficient evidencePaper 3007

Study snapshot

PublicationThe journal of physical chemistry letters · 2014

Study typein_vitro

Reported directionUnclear

Evidence ratingInsufficient

Abstract

The electric fields generated by excited-state electron injection into anatase TiO2 nanocrystallites are screened by cations present in the external electrolyte. With some assumptions, a newly discovered electroabsorption signature enables quantification of the electric field strength experienced by surface-anchored dye molecules. Here, it was found that the fields increased in the order Na(+) < Li(+) < Mg(2+) < Ca(2+), with magnitudes of 1.1 MV/cm for Na(+) and 2.2 MV/cm for Ca(2+), values that were insensitive to whether the anion was iodide or perchlorate. The magnitude of the field was directly related to average TiO2(e(-)) + I3(-) → charge recombination rate constants abstracted from time-resolved kinetic data. Extrapolation to zero field provided an estimate of recombination dynamics when diffusion alone controlled I3(-) mass transport, k = 300 s(-1). The decreased rate constants measured after excited-state injection were attributed to migration of I3(-) away from the TiO2. Cation transference coefficients were tabulated that ranged from t = 0.97 for Ca(2+) to 0.40 for Na(+) and represented the ability of the unscreened electric field to block the TiO2(e(-)) + I3(-) → charge recombination reaction. This data provides the first compelling evidence that the anionic nature of I3(-) inhibits unwanted charge recombination in dye-sensitized solar cells.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typein_vitro

Effect directionunclear

PopulationNot supplied

Sample sizeNot supplied

ExposureNot supplied

Evidence strengthInsufficientConfidence: 74% · Peer reviewed: yes

Main findings

Electroabsorption measurements were used to quantify electric field strengths experienced by dye molecules; fields increased from Na+ (1.1 MV/cm) to Ca2+ (2.2 MV/cm) and were reported as insensitive to whether the anion was iodide or perchlorate. The field magnitude was directly related to TiO2(e−) + I3− charge recombination rate constants derived from time-resolved kinetics; extrapolation to zero field estimated k = 300 s−1 when diffusion alone controlled I3− transport. Decreased recombination rate constants after injection were attributed to I3− migration away from TiO2, and tabulated cation transference coefficients (0.40 for Na+ to 0.97 for Ca2+) were presented as reflecting the ability of the unscreened field to block recombination.

Outcomes measured

Electric field strength at surface-anchored dye molecules (MV/cm)
TiO2(e−) + I3− charge recombination rate constants (s−1)
Cation transference coefficients (t)

Limitations

No organism/human health outcomes; study is on electrochemical/photophysical processes in dye-sensitized solar cells
Sample size and experimental replication not stated in the abstract
Exposure parameters typical for EMF epidemiology (frequency, SAR, duration) not applicable/not reported

View raw extracted JSON

{
  "study_type": "in_vitro",
  "exposure": {
    "band": null,
    "source": "electric fields in dye-sensitized solar cells (electrolyte/cation screening)",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "Electric field strength at surface-anchored dye molecules (MV/cm)",
    "TiO2(e−) + I3− charge recombination rate constants (s−1)",
    "Cation transference coefficients (t)"
  ],
  "main_findings": "Electroabsorption measurements were used to quantify electric field strengths experienced by dye molecules; fields increased from Na+ (1.1 MV/cm) to Ca2+ (2.2 MV/cm) and were reported as insensitive to whether the anion was iodide or perchlorate. The field magnitude was directly related to TiO2(e−) + I3− charge recombination rate constants derived from time-resolved kinetics; extrapolation to zero field estimated k = 300 s−1 when diffusion alone controlled I3− transport. Decreased recombination rate constants after injection were attributed to I3− migration away from TiO2, and tabulated cation transference coefficients (0.40 for Na+ to 0.97 for Ca2+) were presented as reflecting the ability of the unscreened field to block recombination.",
  "effect_direction": "unclear",
  "limitations": [
    "No organism/human health outcomes; study is on electrochemical/photophysical processes in dye-sensitized solar cells",
    "Sample size and experimental replication not stated in the abstract",
    "Exposure parameters typical for EMF epidemiology (frequency, SAR, duration) not applicable/not reported"
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "electric field",
    "electroabsorption",
    "TiO2",
    "dye-sensitized solar cells",
    "charge recombination",
    "triiodide",
    "cations",
    "screening",
    "time-resolved kinetics"
  ],
  "suggested_hubs": []
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1021/jz5016444
PubMed: 26276343

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