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 journalArticle

109 Citations (Scopus)

Abstract

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
Pages (from-to)2218-2226
Number of pages9
JournalChemistry of Materials
Volume23
Issue number8
DOIs
Publication statusPublished - Apr 26 2011

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Transparency
Electronic structure
Heterojunctions
ITO glass
Thin films
Photovoltaic cells
Open circuit voltage
Pulsed laser deposition
Charge carriers
Volatile organic compounds
Passivation
Surface structure
Band structure
Atomic force microscopy
Diodes
Electric properties
Optical properties
Crystal structure
X ray diffraction
Microstructure

Keywords

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

ASJC Scopus subject areas

  • Materials Chemistry
  • Chemical Engineering(all)
  • Chemistry(all)

Cite this

Structural and electrical functionality of NiO interfacial films in bulk heterojunction organic solar cells. / Irwin, Michael D.; Servaites, Jonathan D.; Buchholz, D. Bruce; Leever, Benjamin J.; Liu, Jun; Emery, Jonathan D.; Zhang, Ming; Song, Jung Hwan; Durstock, Michael F.; Freeman, Arthur J; Bedzyk, Michael J.; Hersam, Mark C; Chang, Robert P. H.; Ratner, Mark A; Marks, Tobin J.

In: Chemistry of Materials, Vol. 23, No. 8, 26.04.2011, p. 2218-2226.

Research output: Contribution to journalArticle

Irwin, MD, Servaites, JD, Buchholz, DB, Leever, BJ, Liu, J, Emery, JD, Zhang, M, Song, JH, Durstock, MF, Freeman, AJ, Bedzyk, MJ, Hersam, MC, Chang, RPH, Ratner, MA & Marks, TJ 2011, 'Structural and electrical functionality of NiO interfacial films in bulk heterojunction organic solar cells', Chemistry of Materials, vol. 23, no. 8, pp. 2218-2226. https://doi.org/10.1021/cm200229e
Irwin, Michael D. ; Servaites, Jonathan D. ; Buchholz, D. Bruce ; Leever, Benjamin J. ; Liu, Jun ; Emery, Jonathan D. ; Zhang, Ming ; Song, Jung Hwan ; Durstock, Michael F. ; Freeman, Arthur J ; Bedzyk, Michael J. ; Hersam, Mark C ; Chang, Robert P. H. ; Ratner, Mark A ; Marks, Tobin J. / Structural and electrical functionality of NiO interfacial films in bulk heterojunction organic solar cells. In: Chemistry of Materials. 2011 ; Vol. 23, No. 8. pp. 2218-2226.
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AU - Song, Jung Hwan

AU - Durstock, Michael F.

AU - Freeman, Arthur J

AU - Bedzyk, Michael J.

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AB - 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.

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