Chemical and physical reduction of high valence ni states in mesoporous Nio film for solar cell application

Luca D'Amario, Roger Jiang, Ute B. Cappel, Elizabeth A. Gibson, Gerrit Boschloo, Håkan Rensmo, Licheng Sun, Leif Hammarström, Haining Tian

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)


The most common material for dye-sensitized photocathodes is mesoporous NiO. We transformed the usual brownish NiO to be more transparent by reducing high valence Ni impurities. Two pretreatment methods have been used: Chemical reduction by NaBH4 and thermal reduction by heating. The power conversion efficiency of the cell was increased by 33% through chemical treatment, and an increase in open-circuit voltage from 105 to 225 mV was obtained upon heat treatment. By optical spectroelectrochemistry, we could identify two species with characteristically different spectra assigned to Ni3+ and Ni4+. We suggest that the reduction of surface Ni3+ and Ni4+ to Ni decreases the recombination reaction between holes on the NiO surface with the electrolyte. It also keeps the dye firmly on the surface, building a barrier for electrolyte recombination. This causes an increase in open-circuit photovoltage for the treated film.

Original languageEnglish
Pages (from-to)33470-33477
Number of pages8
JournalACS Applied Materials and Interfaces
Issue number39
Publication statusPublished - Oct 4 2017


  • Characterization
  • Dye-sensitized solar cell
  • Hole UV-vis spectrum
  • P-type
  • Photovoltage
  • Recombination

ASJC Scopus subject areas

  • Materials Science(all)

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