Self-Quenching and Slow Hole Injection May Limit the Efficiency in NiO-Based Dye-Sensitized Solar Cells

Jens Föhlinger, Somnath Maji, Allison M. Brown, Edgar Mijangos, Sascha Ott, Leif Hammarström

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

A series of bis-tridentate ruthenium complexes was designed to feature opposite localizations of their lowest metal-to-ligand charge transfer (MLCT) excited states, relative to a carboxylic acid that served as binding group to mesoporous NiO. The purpose was to study the effiect of MLCT direction on the rates of hole injection into NiO and subsequent charge recombination. Surprisingly, fs-transient absorption spectroscopy showed that the two heteroleptic, cyclometalated complexes of this series did not inject holes into NiO, but their excited states were nevertheless quenched in a rapid process (on the time scale of hundreds of picoseconds). An identical result was obtained for the dyes on non-reactive ZrO2 and we therefore attribute the short MLCT lifetime to self-quenching, due the high surface concentrations of the dyes. We further show that self-quenching on this time scale can potentially compete with hole injection also for functional NiO sensitizers. A ruthenium polypyridine complex, which has previously been used for NiO-based solar cells, was shown to inject holes only very slowly (τ ≈ 5 ns), in contrast to the common notion that hole injection in dye NiO systems is ultrafast (predominantly sub-ps time scale). The hole injection yield was estimated to only ca. 20 %, which matches the reported APCE value of the corresponding device [Freys, J. C.; Gardner, J. M.; D'Amario, L.; Brown, A. M.; Hammarström, L., Dalton Trans. 2012, 41,pp. 13105]. Therefore, we suggest that self-quenching and slow injection might be a reason for the low photovoltaic performance of some p-type dye-sensitized solar cells.

Original languageEnglish
JournalJournal of Physical Chemistry C
DOIs
Publication statusAccepted/In press - Jan 29 2018

Fingerprint

Charge transfer
Quenching
Coloring Agents
Ruthenium
Dyes
solar cells
dyes
Metals
quenching
Ligands
injection
Excited states
charge transfer
Carboxylic Acids
Absorption spectroscopy
Carboxylic acids
ligands
ruthenium
Solar cells
metals

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Self-Quenching and Slow Hole Injection May Limit the Efficiency in NiO-Based Dye-Sensitized Solar Cells. / Föhlinger, Jens; Maji, Somnath; Brown, Allison M.; Mijangos, Edgar; Ott, Sascha; Hammarström, Leif.

In: Journal of Physical Chemistry C, 29.01.2018.

Research output: Contribution to journalArticle

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