Sputter-Deposited Titanium Oxide Layers as Efficient Electron Selective Contacts in Organic Photovoltaic Devices

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

DOI

  • Mina Mirsafaei, University of Southern Denmark, Sønderborg
  • ,
  • Pia Bomholt Jensen
  • Mehrad Ahmadpour, University of Southern Denmark, Sønderborg
  • ,
  • Harish Lakhotiya
  • John Lundsgaard Hansen
  • Brian Julsgaard
  • Horst Günter Rubahn, University of Southern Denmark, Sønderborg
  • ,
  • Rémi Lazzari, Sorbonne Université
  • ,
  • Nadine Witkowski, Sorbonne Université
  • ,
  • Peter Balling
  • Morten Madsen, SDU NanoSYD, University of Southern Denmark, Sønderborg

Organic photovoltaics (OPVs) has recently reached power conversion efficiencies of 17.3%, making it a green technology that not only offers short energy payback times and diverse photovoltaic integration schemes, but also can deliver competitive power outputs. OPVs typically employs electron selective contact layers made from low work function n-type metal oxide semiconductors, such as titanium oxide (TiO2) or zinc oxide (ZnO), developed from a variety of deposition techniques. However, in the case of TiO2 interlayers, the appearance of unwanted s-shape characteristics has been reported extensively in the literature in the past, for a variety of different deposition methods used. It has been shown that the s-shape arises from negatively charged chemisorbed oxygen, and that it can be deactivated by UV light illumination, which, however, is hardly compatible with real-life OPV application. In this work, we introduce sputtered crystalline titanium oxide layers as efficient s-shape-free electron selective extraction layers in organic solar-cell devices. We demonstrate that the onset of crystallization takes place at substrate growth temperatures of approximately 100 °C for the TiOx thin films, and that the crystallization onset temperature correlates well with a strong increase in device performance and the removal of any s-shape characteristics. Optical, structural, compositional, and electronic energy-level characterizations of the TiOx layers are shown in the present work, and point to the formation of an oxide with a low surface-defect density, developed from the sputter-crystallization process. Importantly, well-functioning s-shape-free PTB7:PC70BM devices are demonstrated for TiOx growth temperatures of 155 °C.

Original languageEnglish
JournalACS Applied Energy Materials
Volume3
Issue1
Pages (from-to)253-259
Number of pages7
ISSN2574-0962
DOIs
Publication statusPublished - Jan 2020

    Research areas

  • metal oxide interlayers, organic photovoltaics, s-shape-free, sputter deposition, titanium oxide, TRANSPORT LAYER, POLYMER SOLAR-CELLS, FILM, STABILITY, ANATASE

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