Deng Dan, Zhang Yajie, Zhu Lingyun, Zhang Jianqi, Lu Kun, Wei Zhixiang
National Center for Nanoscience and Technology, Beijing 100190, China.
Phys Chem Chem Phys. 2015 Apr 14;17(14):8894-900. doi: 10.1039/c5cp00042d. Epub 2015 Mar 6.
Self-assembly is crucial for small molecular organic solar cells, which are extremely sensitive to the molecular structure. In this work, three subtle structural changed end-capped acceptors with increased electron withdrawing ability, named octyl 2-cyanoacetate (=CNCOOC8H17), 3-oxoundecanenitrile (=CNCOC8H17), and 2-(octylsulfonyl) acetonitrile (=CNSOOC8H17), were synthesized and introduced into a planar conjugated backbone using ethylhexyl-thiophene substituted benzodithiophene (TBDT) as a core and trithiophene as a π-bridge (labelled M1, M2 and M3, respectively). Their effects on absorption, thermal properties, and morphologies were studied and compared. In particular, the molecular packing of the three materials varied significantly, and the hole mobilities differed by orders of magnitude. As a result, the fill factors of devices varied from 52% to 72%. Combining the effects of electron-withdrawing capability and molecular packing, the power conversion efficiencies of the optimized devices increased from 3.0% for M3 to 6.4% for M1 and M2. The relationship between end-capped acceptors and photovoltaic properties would generate valuable insights into further producing more efficient solution-processable organic solar cells.
自组装对于小分子有机太阳能电池至关重要，这类电池对分子结构极其敏感。在本工作中，合成了三种末端封端受体，其具有细微的结构变化且吸电子能力增强，分别为氰基乙酸辛酯（=CNCOOC8H17）、3-氧代十一腈（=CNCOC8H17）和2-(辛基磺酰基)乙腈（=CNSOOC8H17），并将它们引入到以乙基己基噻吩取代的苯并二噻吩（TBDT）为核心、三噻吩为π桥的平面共轭主链中（分别标记为M1、M2和M3）。研究并比较了它们对吸收、热性能和形貌的影响。特别地，这三种材料的分子堆积有显著差异，空穴迁移率相差几个数量级。结果，器件的填充因子在52%至72%之间变化。综合吸电子能力和分子堆积的影响，优化器件的功率转换效率从M3的3.0%提高到M1和M2的6.4%。末端封端受体与光伏性能之间的关系将为进一步生产更高效的可溶液加工有机太阳能电池提供有价值的见解。
