Revealing Ordered Polymer Packing during Freeze-Drying Fabrication of a Bulk Heterojunction Poly(3-hexylthiophene-2,5-diyl):[6,6]-Phenyl-C61-butyric Acid Methyl Ester Layer: In Situ Optical Spectroscopy, Molecular Dynamics Simulation, and X-ray Diffraction
Journal
Journal of Physical Chemistry C
Journal Volume
121
Journal Issue
27
Pages
14826-14834
Date Issued
2017
Author(s)
Abstract
Formation of ordered poly(3-hexylthiophene-2,5-diyl) (P3HT) molecular stacking during the freeze-drying process is tracked with in situ spectroscopy of Raman scattering, absorption, and photoluminescence. Raman spectra of pristine P3HT dissolved in 1,2-dichlorobenzene show that P3HT polymers undergo drastic ordered aggregation upon being lower than 0 °C, at which the solubility of P3HT is reached, as evidenced by the emergence of pronounced red-shifted, narrow Raman peaks (1422 and 1435 cm-1) caused by intermolecular coupling. The absorption and photoluminescence spectra bear similar temperature dependence as the results of Raman. Aggregation of P3HT is further confirmed by coarse-grained molecular dynamics simulation showing the enhanced order parameters of distance and orientation between P3HT chains upon cooling. The incorporation of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) does not significantly alter the P3HT packing configuration, as verified by nearly identical Raman features observed in P3HT:PCBM mixing solution upon cooling. While optical spectroscopy and MD simulation portrayed the short-range order of P3HT aggregates, grazing-incident X-ray diffraction exposed the long-range order by the pronounced diffraction spots corresponding to the lamellar stacking of P3HT. This study demonstrates the ability of Raman spectroscopy to reveal the short-range order of polymer packing, while the in situ monitoring illustrates that the ability of freeze-drying to separate molecular aggregation from solvent removal thus is advantageous for photovoltaic device fabrication without resorting to trial and error. © 2017 American Chemical Society.
SDGs
Other Subjects
Carrier mobility; Drying; Esters; Heterojunctions; Low temperature drying; Molecular dynamics; Molecular orientation; Photoluminescence; Polymers; Raman scattering; X ray diffraction; Absorption and photoluminescence; Coarse-grained molecular dynamics simulations; Grazing-incident X-ray diffractions; In-situ optical spectroscopy; Intermolecular coupling; Molecular dynamics simulations; Poly(3-hexylthiophene-2 ,5-diyl); [6 ,6]-phenyl-C61-butyric acid methyl esters; Butyric acid
Publisher
American Chemical Society
Type
journal article