Title: Structural Evolution of Crystalline Conjugated Polymer/Fullerene Domains from Solution to the Solid State in the Presence and Absence of an Additive
Authors: Su, Yu-Wei
Liu, Chih-Ming
Jiang, Jian-Ming
Tsao, Cheng-Si
Cha, Hou-Chin
Jeng, U-Ser
Chen, Hsing-Lung
Wei, Kung-Hwa
Department of Materials Science and Engineering
Issue Date: 12-Feb-2015
Abstract: The power conversion efficiencies of polymer/fullerene solar cells are critically dependent on the nanometer-scale morphologies of their active layers, which are typically processed from solution. Using synchrotron wide- and small-angle X-ray scattering, we have elucidated the intricate mechanism of the structural transitions from solutions to solid films of the crystalline polymer poly[bis(dodecyl)thiophene-thieno[3,4-c]pyrrole-4,6-dione] (PBTTPD) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM), including the effect of the solvent additive 1,6-diiodohexane (DIH). We found that the local assembly of rigid-rod PBTTPD segments that formed in solution instantly and then relaxed within several hundred seconds upon cooling to room temperature from 90 degrees C could re-emerge and develop into seeds for subsequent crystallization of the polymer in the solid films. At room temperature (25 degrees C), the presence of DIH in chlorobenzene slightly enhanced the formation of local assembly PBTTPD segments in the supersaturated PBTTPD in PBTTPD/PC71BM blend solution. Two cases of films were subsequently developed from these blend solutions with drop-casted and spin-coated methods. For spin-coated thin films (90 nm thick), which evolve quickly, polymers crystallinity and the fullerene packing in the solid-state thin films were enhanced in the case of involving DIH. Regarding the effect of DIH for processing the drop-casted thick films (2.5 mu m thick), which evolve slowly, DIH has no observable effect on PBTTPD/PC71BM structure. Our results provide some understanding of the mechanism behind the structural development of polymer/fullerene blends upon their transitions from solution to the solid state, as well as the key functions of the additive.
URI: http://dx.doi.org/10.1021/jp512315a
ISSN: 1932-7447
DOI: 10.1021/jp512315a
Volume: 119
Begin Page: 3408
End Page: 3417
Appears in Collections:Articles