Formation of interfacial traps upon surface protonation in small molecule solution processed bulk heterojunctions probed by photoelectron spectroscopy

Erin L Ratcliff, Ronald C. Bakus, Gregory C. Welch, Tom S. Van Der Poll, Andres Garcia, Sarah R. Cowan, Bradley A. MacLeod, David S. Ginley, Guillermo C. Bazan, Dana C. Olson

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

This work expands on the recently reported protonation of the donor molecule 7,7′-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′] dithiophene-2,6-diyl)bis(4-(5′-hexyl-[2,2′-bithiophen]-5-yl)-[1,2,5] thiadiazolo[3,4-c]pyridine) (d-DTS(PTTh2)2) by the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) interlayer to include an electrostatic picture of interfacial energetic states. Ultraviolet photoemission spectroscopy results initially suggested favorable band level alignment for hole extraction between d-DTS(PTTh2)2 and PEDOT:PSS. However photovoltaic device performance yields a low fill factor and photovoltage, indicative of poor hole-extraction at the hole-collecting interface, relative to the nickel oxide device. Further investigation into the interfacial composition via theory and X-ray photoelectron studies of both the interface and a control system of d-DTS(PTTh2)2 reacted with p-toluenesulfonic acid verify the presence of a chemically unique species at the interface arising from protonation reaction with the residual acidic protons present in PEDOT:PSS that was masked in the UPS experiment. From these results, the energy band diagram is re-interpreted to account for the interfacial chemical reaction and modified interfacial density of states. Additionally, the detrimental protonation reaction is avoided when the pyridyl[1,2,5]thiadiazole acceptor unit was replaced with a 5-fluorobenzo[c][1, 2,5]thiadiazole acceptor unit, which shows no such reaction with the PEDOT:PSS substrate. These results indicate the necessity of using a large analytical toolkit to elucidate the energetics and mechanisms of buried interfaces that will impact dynamics of hole collection.

Original languageEnglish (US)
Pages (from-to)6223-6234
Number of pages12
JournalJournal of Materials Chemistry C
Volume1
Issue number39
DOIs
StatePublished - Oct 21 2013

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Protonation
Photoelectron spectroscopy
Heterojunctions
Thiadiazoles
Molecules
Nickel oxide
Photoelectrons
Ultraviolet spectroscopy
Pyridine
Band structure
Chemical reactions
Electrostatics
Protons
Control systems
X rays
Acids
Substrates
Chemical analysis
poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)
Experiments

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Chemistry

Cite this

Formation of interfacial traps upon surface protonation in small molecule solution processed bulk heterojunctions probed by photoelectron spectroscopy. / Ratcliff, Erin L; Bakus, Ronald C.; Welch, Gregory C.; Van Der Poll, Tom S.; Garcia, Andres; Cowan, Sarah R.; MacLeod, Bradley A.; Ginley, David S.; Bazan, Guillermo C.; Olson, Dana C.

In: Journal of Materials Chemistry C, Vol. 1, No. 39, 21.10.2013, p. 6223-6234.

Research output: Contribution to journalArticle

Ratcliff, EL, Bakus, RC, Welch, GC, Van Der Poll, TS, Garcia, A, Cowan, SR, MacLeod, BA, Ginley, DS, Bazan, GC & Olson, DC 2013, 'Formation of interfacial traps upon surface protonation in small molecule solution processed bulk heterojunctions probed by photoelectron spectroscopy', Journal of Materials Chemistry C, vol. 1, no. 39, pp. 6223-6234. https://doi.org/10.1039/c3tc31064g
Ratcliff, Erin L ; Bakus, Ronald C. ; Welch, Gregory C. ; Van Der Poll, Tom S. ; Garcia, Andres ; Cowan, Sarah R. ; MacLeod, Bradley A. ; Ginley, David S. ; Bazan, Guillermo C. ; Olson, Dana C. / Formation of interfacial traps upon surface protonation in small molecule solution processed bulk heterojunctions probed by photoelectron spectroscopy. In: Journal of Materials Chemistry C. 2013 ; Vol. 1, No. 39. pp. 6223-6234.
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AU - Garcia, Andres

AU - Cowan, Sarah R.

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