Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV16)
Publication date: 28th March 2016
Tetrazines have been successfully applied as electron-deficient building blocks in donor-acceptor copolymers. [1] These strong acceptors can be straightforwardly obtained from the corresponding nitriles. One currently limiting factor, however, is their poor solubility, which requires electron-rich comonomers with large solubilising alkyl chains. This is also the case for benzothiadiazole, one of the most successful electron-deficient units to date. To improve solubility and processability, 2,1,3-benzothiadiazole-5,6-dicarboxylic imide has been developed and copolymers with this acceptor unit led to excellent efficiencies of over 8% without requiring processing additives or additional processing steps such as thermal annealing. [2] This also allows variation of the alkyl chains on both electron-rich and electron-deficient components to tailor the alkyl chain substitution pattern, which has a profound influence on blend morphology and consequently device performance. [3] Inverse-electron-demand Diels-Alder reactions of tetrazines and N-alkyl substituted maleimides resulted in 6-alkylpyrrolo[3,4-d]pyridazine-5,7-diones (PPD). [4] In this modular synthetic approach, alkyl chains and flanking aromatic units can be easily varied to study structure-property relationships. The PPD monomers are obtained in good yield and purity. In this contribution we will discuss the preparation of these monomers and novel polymers derived from Pd-catalyzed Stille and Suzuki-type polymerizations and their properties with respect to photovoltaic devices.
[1] Li, Z.; Ding, J.; Song, N.; Lu, J.; Tao, Y., J. Am. Chem. Soc., 2010, 132, 13160-13161.
[2] Nielsen, C. B.; Ashraf, R. S.; Treat, N. D.; Schroeder, B. C.; Donaghey, J. E.; White, A. J. P.; Stingelin, N.; McCulloch, I., Adv. Mater., 2015, 27, 948-953.
[3] McCulloch, I.; Ashraf, R. S.; Biniek, L.; Bronstein, H.; Combe, C.; Donaghey, J. E.; James, D. I.; Nielsen, C. B.; Schroeder, B. C.; Zhang W., Acc. Chem. Res., 2012, 45, 714-722.
[4] Ye, Q.; Neo, W. T.; Cho, C. M.; Yang, S. W.; Lin, T.; Zhou, H.; Yan, H.; Lu, X.; Chi, C.; Xu, J., Org. Lett., 2014, 16, 6386-6389.