Contact-induced mechanisms in organic photovoltaics: A steady-state and transient study

Sarah R. Cowan, Jian V. Li, Dana C. Olson, Erin L Ratcliff

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The role of the contacts in thin-film, blended heterojunctions (<100 nm thick) organic photovoltaics is explored, specifically considering concepts of carrier selectivity, injection, and extraction efficiency, relative to recombination. Contact effects are investigated by comparing two hole-collecting interlayers: a phosphonic acid monolayer on indium tin oxide (ITO) and a nickel oxide thin film. The interlayers have equivalent work functions (≈5.4 eV) but widely variant energy band offsets relative to the lowest unoccupied molecular orbital of the acceptor (electron blocking versus not), which are coupled to large differences in carrier density. Trends in open-circuit voltages (VOC) as a function of light intensity and temperature are compared and it is concluded that the dominant mechanism limiting VOC for high density of states contacts is free carrier injection, not surface recombination or extraction barriers. Transient photocurrent decay measurements confirm excess reinjected carriers decrease the extraction efficiency via increased recombination and decrease free carrier lifetime, even at high internal electric fields, due to space charge accumulation. These results demonstrate that the energetics and injection dynamics of the interface between interlayers and high carrier density electrodes (typically ITO and metals) must be considered with fabrication and processing of interlayers, in addition to possible carrier selectivity and the interface with the active layer.

Original languageEnglish (US)
Article number1400549
JournalAdvanced Energy Materials
Volume5
Issue number1
DOIs
StatePublished - Jan 1 2015

Fingerprint

Tin oxides
Volatile organic compounds
Indium
Carrier concentration
Thin films
Nickel oxide
Carrier lifetime
Molecular orbitals
Open circuit voltage
Photocurrents
Electric space charge
Band structure
Oxide films
Heterojunctions
Monolayers
Metals
Electric fields
Fabrication
Electrodes
Acids

Keywords

  • Characterization tools
  • Charge transport
  • Electrodes
  • Organic electronics

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

Cite this

Contact-induced mechanisms in organic photovoltaics : A steady-state and transient study. / Cowan, Sarah R.; Li, Jian V.; Olson, Dana C.; Ratcliff, Erin L.

In: Advanced Energy Materials, Vol. 5, No. 1, 1400549, 01.01.2015.

Research output: Contribution to journalArticle

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