The Importance of Microstructure in Determining Polaron Generation Yield in Poly(9,9-dioctylfluorene)

Nathan J. Cheetham, Manuel Ortiz, Aleksandr Perevedentsev, Laura Isabelle Dion-Bertrand, Gregory M. Greetham, Igor V. Sazanovich, Michael Towrie, Anthony W. Parker, Jenny Nelson, Carlos Silva, Donal D.C. Bradley, Sophia C. Hayes, Paul N. Stavrinou

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Understanding the structure-property relationships that govern exciton dissociation into polarons in conjugated polymers is key in developing materials for optoelectronic applications such as light-emitting diodes and solar cells. Here, the polymer poly(9,9-dioctylfluorene) (PFO), which can form a minority population of chain segments in a distinct, lower-energy "β-phase" conformation, is studied to examine the influence of conformation and microstructure on polaron generation in neat thin films. Through use of ultrafast transient absorption spectroscopy to probe PFO thin films with glassy-phase and β-phase microstructures and selectively exciting each phase independently, the dynamics of exciton dissociation are resolved. Ultrafast polaron generation is consistently found to be significantly higher and long-lived in thin films containing β-phase chain segments, with an average polaron yield that increases by over a factor of three to 4.9% vs 1.4% in glassy-phase films. The higher polaron yield, attributed to an increased exciton dissociation yield at the interface between conformational phases, is most likely due to a combination of the significant energetic differences between glassy-phase and β-phase segments and disparities in electronic delocalization and charge carrier mobilities between phases.
Original languageEnglish (US)
JournalChemistry of Materials
Volume31
Issue number17
DOIs
StatePublished - Sep 10 2019
Externally publishedYes

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