| Autor: |
Tiwari V; European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany., Li X; Division of Theoretical Chemistry & Biology, KTH Royal Institute of Technology, SE-10691 Stockholm, Sweden., Li Z; State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China.; Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China.; Yangtze Delta Institute of Optoelectronics, Peking University Nantong, Jiangsu 226010, China., Jacobs IE; Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, U.K., Duan HG; Department of Physics, School of Physical Science & Technology, Ningbo University, Ningbo 315211, P. R. China., Sirringhaus H; Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, U.K., Miller RJD; Departments of Chemistry & Physics, University of Toronto, Toronto M5S 3H6, Canada., Jha A; Rosalind Franklin Institute, Harwell, Oxfordshire OX11 0QX, U.K.; Department of Pharmacology, University of Oxford, Oxford OX1 3QT, U.K. |
| Abstrakt: |
Spin-casting of molecularly doped polymer solution mixtures is one of the commonly used methods to obtain conductive organic semiconductor films. In spin-casted films, electronic interaction between the dopant and polymer is one of the crucial factors that dictates the doping efficiency. Here, we investigate excitonic couplings using ultrafast two-dimensional electronic spectroscopy to examine the different types of electronic interactions in ion pairs of the prototype F 4 TCNQ-doped P3HT polymer system in a precursor solution mixture for spin-casting. Off-diagonal peaks in the 2D spectra clearly establish the excitonic coupling between P3HT + and F 4 TCNQ - ions in solution. The observed excitonic coupling is the direct manifestation of a Coulombic interaction between the ion pair. The excited-state lifetime of F 4 TCNQ - in ion pairs shows biexponential decay at 30 and 200 fs, which hints toward the presence of a heterogeneous population with different interaction strengths. To examine the nature of these different types of interactions in solution mixtures, we study the system using molecular dynamics simulations on a fully solvated model employing the generalized Amber force field. We retrieve three dominant interaction modes of F 4 TCNQ anions with P3HT: side chain, π-stack, and slipped stack. To quantify these interactions, we complement our studies with electronic structure calculations, which reveal the excitonic coupling strengths of ∼ 75 cm -1 for side chain, ∼ 150 cm -1 for π-π-stack, and ∼69 cm -1 for slipped stack. These various interaction modes provide information about the key geometries of the seed structures in precursor solution mixtures, which may determine the final structures in spin-casted films. The insights gained from our study may guide new strategies to control and ultimately tune Coulomb interactions in polymer-dopant solutions. |
