Tuning crystalline ordering by annealing and additives to study its effect on exciton diffusion in a polyalkylthiophene copolymer
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The influence of various processing conditions on the singlet exciton diffusion is explored in films of a conjugated random copolymer poly-(3-hexylthiophene-co-3-dodecylthiophene) (P3HT-co-P3DDT) and correlated with the degree of crystallinity probed by grazing incidence X-ray scattering and with exciton bandwidth determined from absorption spectra. The exciton diffusion coefficient is deduced from exciton-exciton annihilation measurements and is found to increase by more than a factor of three when thin films are annealed using CS2 solvent vapour. A doubling of exciton diffusion coefficient is observed upon melt annealing at 200 °C and the corresponding films show about 50% enhancement in the degree of crystallinity. In contrast, films fabricated from polymer solutions containing a small amount of either solvent additive or nucleating agent show a decrease in exciton diffusion coefficient possibly due to formation of traps for excitons. Our results suggest that the enhancement of exciton diffusivity occurs because of increased crystallinity of alkyl-stacking and longer conjugation of aggregated chains which reduces the exciton bandwidth.
Chowdhury , M , Sajjad , M T , Savikhin , V , Hergue , N , Sutija , K , Oosterhout , S , Toney , M F , Dubois , P , Ruseckas , A & Samuel , I D W 2017 , ' Tuning crystalline ordering by annealing and additives to study its effect on exciton diffusion in a polyalkylthiophene copolymer ' Physical Chemistry Chemical Physics , vol 19 , pp. 12441-12451 . DOI: 10.1039/C7CP00877E
Physical Chemistry Chemical Physics
Copyright the Authors 2017. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
M.C, M.T.S, A.R and I.D.W.S acknowledge support from the European Research Council (EXCITON grant 321305). I.D.W.S acknowledges Royal Society Wolfson Research Merit Award. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515
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