The Importance of Microstructure in Determining Polaron Generation Yield in Poly(9,9-dioctylfluorene)
Date
2019Author
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.
ISSN
0897-4756Source
Chemistry of MaterialsVolume
31Issue
17Pages
6787-6797Google Scholar check
Metadata
Show full item recordAbstract
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.