Relaxation of electron carriers in the density of states of nanocrystalline TiO2

Luca Bertoluzzi, Isaac Herraiz-Cardona, Ronen Gottesman, Arie Zaban, Juan Bisquert*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations

Abstract

Band gap localized states and surface states play a dominant role in the application of nanocrystalline metal oxides to photovoltaics and solar fuel production. Electrons injected in nanocrystalline TiO2 by voltage or photogeneration are mainly located in band gap states. Therefore, charging a nanoparticulate semiconductor network allows one to recover the density of states (DOS) in the energy axis. However, shallow traps remain in equilibrium with the conduction band electrons, while deep traps do not. We show that the characteristic peak of the apparent DOS mixes an exponential DOS and a monoenergetic surface state. A model that incorporates the trap's kinetics proves to be very efficient to assess the important parameters that determine both contributions via variation of charging rate. Contrary to the common theory, we demonstrate that the peculiar capacitance peak of nanocrystalline TiO2 can be mainly attributed, in some cases, to deep traps in the exponential distribution.

Original languageAmerican English
Pages (from-to)689-694
Number of pages6
JournalJournal of Physical Chemistry Letters
Volume5
Issue number4
DOIs
StatePublished - 20 Feb 2014
Externally publishedYes

Keywords

  • chemical capacitance
  • cyclic voltammetry
  • demarcation level
  • kinetics
  • localized states

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