ИСТИНА

Star-shaped oligothiophenes (SSO) are promising materials for high-efficient and stable organic photovoltaics. The SSO-based solar cells have shown the efficiency higher than 5%; and its further enhancement needs optimization of the SSO molecular structure. In this work, we study new SSOs with increased solubility due to addition of methoxygroups to the triphenylamine core. The SSO molecular structure was tuned via variation of the number of thiophene rings and the length of alkyl end groups. The dependence of photovoltaic properties of new SSOs on their molecular structure was studied. The efficiencies of organic solar cells based on the SSOs with alkyl end groups blended with PC71BM were near 3%. It was found that efficiency increases with the number of thiophene rings from 2 to 3 in the star ray and with alkyl end group length from 1 to 6 carbon atoms mainly due to increase of the short-circuit current and fill factor. However, the dependence of the open-circuit voltage is reverse. For the SSO without alkyl groups the open-circuit voltage is maximal and the leakage currents are very low, but the efficiency and photocurrent are 1.5 – 2 times lower compared with other SSO. All studied SSOs showed high stability during storage in bookshelf conditions. The effect of the SSO molecular structure on the photovoltaic performance and further optimization pathways are discussed. The work was supported by Russian Science Foundation (grant 14-13-01380).