Effect of annealing on the sub-bandgap, defects and trapping states of ZnO nanostructures

Ruri Agung Wahyuono, Felix Hermann-Westendorf, Andrea Dellith, Christa Schmidt, Jan Dellith, Jonathan Plentz, Martin Schulz, Martin Presselt, Martin Seyring, Markus Rettenmeyer, Benjamin Dietzek*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


Annealing treatment was applied to different mesoporous ZnO nanostructures prepared by wet chemical synthesis, i.e. nanoflowers (NFs), spherical aggregates (SPs), and nanorods (NRs). The sub-bandgap, defect properties as well as the trapping state characteristics after annealing were characterized spectroscopically, including ultrasensitive photothermal deflection spectroscopy (PDS), photoluminescence and photo-electrochemical methods. The comprehensive experimental analysis reveals that annealing alters both the bandgap and the sub-bandgap. The defect concentration and the density of surface traps in the ZnO nanostructures are suppressed upon annealing as deduced from photoluminescence and open-circuit voltage decay analysis. The photo-electrochemical investigations reveal that the surface traps dominate the near conduction band edge of ZnO and, hence, lead to high recombination rates when used in DSSCs. The density of bulk traps in ZnO SPs is higher than that in ZnO NFs and ZnO NRs and promote lower recombination loss between photoinjected electrons with the electrolyte-oxidized species on the surface. The highest power conversion efficiency of ZnO NFs-, ZnO SPs-, and ZnO NRs-based DSSC obtained in our system is 2.0, 4.5, and 1.8%, respectively.

Original languageEnglish
Pages (from-to)112-121
Number of pages10
JournalChemical Physics
Publication statusPublished - 1 Feb 2017


  • Bulk traps
  • Dye-sensitized solar cells
  • OCVD
  • PDS
  • Surface traps
  • ZnO


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