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

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...

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Veröffentlicht in:Chemistry of materials 2019-09, Vol.31 (17), p.6787-6797
Hauptverfasser: Cheetham, Nathan J, Ortiz, Manuel, Perevedentsev, Aleksandr, Dion-Bertrand, Laura-Isabelle, Greetham, Gregory M, Sazanovich, Igor V, Towrie, Michael, Parker, Anthony W, Nelson, Jenny, Silva, Carlos, Bradley, Donal D. C, Hayes, Sophia C, Stavrinou, Paul N
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Sprache:eng
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Zusammenfassung: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.
ISSN:0897-4756
1520-5002
DOI:10.1021/acs.chemmater.9b01256