Structural and electrical functionality of NiO interfacial films in bulk heterojunction organic solar cells

Michael D. Irwin, Jonathan D. Servaites, D. Bruce Buchholz, Benjamin J. Leever, Jun Liu, Jonathan D. Emery, Ming Zhang, Jung Hwan Song, Michael F. Durstock, Arthur J. Freeman, Michael J. Bedzyk, Mark C. Hersam, Robert P H Chang, Mark A. Ratner, Tobin J. Marks

Research output: Contribution to journalArticlepeer-review

161 Scopus citations


The functionality of NiO interfacial layers in enhancing bulk heterojunction (BHJ) organic photovoltaic (OPV) cell performance is investigated by integrated characterization of the electrical properties, microstructure, electronic structure, and optical properties of thin NiO films grown on glass/ITO electrodes. These NiO layers are found to be advantageous in BHJ OPV applications due to favorable energy band levels, interface passivation, p-type character, crystallinity, smooth surfaces, and optical transparency. The NiO overlayers are fabricated via pulsed-laser deposition and found to have a work function of ∼5.3 eV. They are investigated by both topographic and conductive atomic force microscopy and shown to passivate interfacial charge traps. The films also have an average optical transparency of >80% in the visible range, crucial for efficient OPV function, and have a near-stoichiometric Ni:O surface composition. By grazing-incidence X-ray diffraction, the NiO thin films are shown to grow preferentially in the (111) direction and to have the fcc NaCl crystal structure. Diodes of p-n structure and first-principles electronic structure calculations indicate that the NiO interlayer is preferentially conductive to holes, with a lower hole charge carrier effective mass versus that of electrons. Finally, the implications of these attributes in advancing efficiencies for state-of-the-art OPV systems-in particular, improving the open circuit voltage (VOC)-are discussed.

Original languageEnglish (US)
Pages (from-to)2218-2226
Number of pages9
JournalChemistry of Materials
Issue number8
StatePublished - Apr 26 2011


  • NiO
  • electron blocking layer
  • hole transport layer
  • interfacial layer
  • nickel oxide
  • organic photovoltaics
  • organic solar cells

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Materials Chemistry


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