Structural Evolution of Crystalline Conjugated Polymer/Fullerene Domains from Solution to the Solid State in the Presence and Absence of an Additive

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• 作者：Yu-Wei Su ; Chih-Ming Liu ; Jian-Ming Jiang ; Cheng-Si Tsao ; Hou-Chin Cha ; U-Ser Jeng ; Hsing-Lung Chen ; Kung-Hwa Wei
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：February 12, 2015
• 年：2015
• 卷：119
• 期：6
• 页码：3408-3417
• 全文大小：664K
• ISSN：1932-7455

文摘

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-C₇₁-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 掳C could re-emerge and develop into seeds for subsequent crystallization of the polymer in the solid films. At room temperature (25 掳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, polymer鈥檚 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 渭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.