Sugiyama Fumitaka, Kleinschmidt Andrew T, Kayser Laure V, Rodriquez Daniel, Finn Mickey, Alkhadra Mohammad A, Wan Jeremy M-H, Ramírez Julian, Chiang Andrew S-C, Root Samuel E, Savagatrup Suchol, Lipomi Darren J
Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, CA 92093-0448.
JSR Corporation, 1-9-2, Higashi-Shimbashi, Minato-ku, Tokyo 105-8640, Japan.
Polym Chem. 2018 Sep 7;9(33):4354-4363. doi: 10.1039/C8PY00820E. Epub 2018 Jul 30.
This paper describes effects of the flexibility, length, and branching of side chains on the mechanical properties of low-bandgap semiconducting polymers. The backbones of the polymer chains comprise a diketopyrrolopyrrole (DPP) motif flanked by two furan rings and copolymerized by Stille polycondensation with thiophene (DPP2FT). The side chains of the DPP fall into three categories: linear alkyl (C8, C14, or C16), branched alkyl (ethylhexyl, EH, or hexyldecyl, HD), and linear oligo(ethylene oxide) (EO3, EO4, or EO5). Polymers bearing C8 and C14 side chains are obtained in low yields and thus not pursued. Thermal, mechanical, and electronic properties are plotted against the number of carbon and oxygen atoms in the side chain. We obtain consistent trends in the thermal and mechanical properties for branched alkyl and linear oligo(ethylene oxide) side chains. For example, the glass transition temperature ( ) and elastic modulus decrease with increasing number of carbon and oxygen atoms, whereas the crack-onset strain increases. Among polymers with side chains of 16 carbon and oxygen atoms (C16, HD, and EO5), C16 exhibits the highest and the greatest susceptibility to fracture. Hole mobility, as measured in thin-film transistors, appears to be a poor predictor of electronic performance for polymers blended with [60]PCBM in bulk heterojunction (BHJ) solar cells. For example, while EO3 and EO4 exhibit the lowest mobilities (< 10 cm V s) in thin-film transistors, solar cells made using these materials performed the best (efficiency > 2.6%) in unoptimized devices. Conversely, C16 exhibits the highest mobility (≈ 0.2 cm V s) but produces poor solar cells (efficiency < 0.01%). We attribute the lack of correlation between mobility and power conversion efficiency to unfavorable morphology in the BHJ solar cells. Given the desirable properties measured for EO3 and EO4, the use of flexible oligo(ethylene oxide) side chains is a successful strategy to impart mechanical deformability to organic solar cells, without sacrificing electronic performance.
本文描述了侧链的柔韧性、长度和支化对低带隙半导体聚合物机械性能的影响。聚合物链的主链包含一个二酮吡咯并吡咯（DPP）基序，两侧各有一个呋喃环，并通过Stille缩聚与噻吩共聚（DPP2FT）。DPP的侧链分为三类：线性烷基（C8、C14或C16）、支化烷基（乙基己基，EH，或己基癸基，HD）和线性聚环氧乙烷（EO3、EO4或EO5）。带有C8和C14侧链的聚合物产率较低，因此未作进一步研究。热性能、机械性能和电子性能与侧链中的碳和氧原子数作图。对于支化烷基和线性聚环氧乙烷侧链，我们在热性能和机械性能方面获得了一致的趋势。例如，玻璃化转变温度（ ）和弹性模量随着碳和氧原子数的增加而降低，而裂纹起始应变增加。在具有16个碳和氧原子侧链的聚合物（C16、HD和EO5）中，C16表现出最高的 以及最大的断裂敏感性。在薄膜晶体管中测量的空穴迁移率，对于在体异质结（BHJ）太阳能电池中与[60]PCBM混合的聚合物来说，似乎并不能很好地预测其电子性能。例如，虽然EO3和EO4在薄膜晶体管中表现出最低的迁移率（< 10 cm V s），但使用这些材料制成的太阳能电池在未优化的器件中表现最佳（效率> 2.6%）。相反，C16表现出最高的迁移率（≈ 0.2 cm V s），但制成的太阳能电池性能很差（效率< 0.01%）。我们将迁移率与功率转换效率之间缺乏相关性归因于BHJ太阳能电池中不利的形态。鉴于EO3和EO4所测得的理想性能，使用柔性聚环氧乙烷侧链是一种成功的策略，可在不牺牲电子性能的情况下赋予有机太阳能电池机械变形能力。
