Chen Jiale, Huang Xuelong, Cao Zhixiong, Liu Shengjian, Liang Kexin, Liu Jinhai, Jiao Xuechen, Zhao Jiaji, Li Qingduan, Cai Yue-Peng
School of Chemistry, Guangzhou Key Laboratory of Materials for Energy Conversion and Storage, Guangdong Provincial Engineering Technology Research Center for Materials for Energy Conversion and Storage, South China Normal University (SCNU), Guangzhou, 510006, P. R. China.
College of Pharmacy, Gannan Medical University, Ganzhou, 341000, P. R. China.
Chemphyschem. 2020 May 5;21(9):908-915. doi: 10.1002/cphc.202000176. Epub 2020 Apr 1.
For all-polymer solar cells which are composed of polymer donors and polymer acceptors, the effect of alkyl side chains on photovoltaic performance is a matter of some debate, and this effect remains difficult to forecast. In this concise contribution, we demonstrate that three alkyls namely branched alkyl 2-butyloctyl (2BO), long linear alkyl n-dodecyl (C12), and double-short linear alkyl n-hexyls (DC6) incorporated into the side chains of large bandgap polymer donor PBDT-TTz can induce considerable, of significance, and different electronic, optical, and morphological parameters. Systematic studies shed light on the critical role of the double-short linear alkyl n-hexyls (DC6) in (i) producing large ionization potential value, (ii) increasing propensity of the polymer to order along the π-stacking direction, (iii) generating polymer crystallites with more preferential "face-on" orientation, consequently, (iv) improvement of carriers transportation, (v) suppression of charge recombination, (vi) reduction of energy loss in all-polymer devices. In parallel, we unearth that the PBDT-TTz with double-short linear alkyl n-hexyls (DC6) represents the highest efficiency of 8.3 %, whereas, the other two PBDT-TTz analogues (2BO, C12) yield efficiencies of less than 3 % in optimized all-polymer solar cells. Though branched or long linear alkyl side chains (2BO, C12) have been applied to provide the solution processability of conjugated polymers, motifs bearing multiple short linear alkyl substituents (DC6) are proved critical to the development of high performing polymers.
对于由聚合物给体和聚合物受体组成的全聚合物太阳能电池，烷基侧链对光伏性能的影响存在一定争议，且这种影响仍难以预测。在本简要论文中，我们证明了引入到大带隙聚合物给体PBDT-TTz侧链中的三种烷基，即支链烷基2-丁基辛基（2BO）、长直链烷基正十二烷基（C12）和双短直链烷基正己基（DC6），可诱导出相当大的、具有重要意义的且不同的电子、光学和形态学参数。系统研究揭示了双短直链烷基正己基（DC6）在以下方面的关键作用：（i）产生较大的电离势值；（ii）增加聚合物沿π堆积方向有序排列的倾向；（iii）生成具有更优先“面朝上”取向的聚合物微晶，因此，（iv）改善载流子传输；（v）抑制电荷复合；（vi）降低全聚合物器件中的能量损失。同时，我们发现带有双短直链烷基正己基（DC6）的PBDT-TTz在优化的全聚合物太阳能电池中代表着最高8.3%的效率，而另外两种PBDT-TTz类似物（2BO、C12）在优化的全聚合物太阳能电池中的效率低于3%。尽管支链或长直链烷基侧链（2BO、C12）已被用于提供共轭聚合物的溶液可加工性，但带有多个短直链烷基取代基的基团（DC6）被证明对高性能聚合物的开发至关重要。
