A nonionic surfactant simultaneously enhancing wetting property and electrical conductivity of PEDOT:PSS for vacuum-free organic solar cells

In this work, we report a nonionic surfactant (polyethylene glycol 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol ether, PEG-TmDD) that can improve the wetting property of PEDOT:PSS aqueous solution on the organic photoactive layer and simultaneously enhance the electrical conductivity of PEDOT:PSS film up to 526 S/cm. Furthermore, the conductivity enhancement is significantly dependent on the thermal annealing, which is contrary to the conductivity behavior of PEDOT:PSS film prepared from the formulation added with ethylene glycol (EG) where the conductivity is almost independent of the thermal annealing. The temperature dependence of the conductivity of PEDOT:PSS by PEG-TmDD is possibly ascribed to decomposition of PEG-TmDD into EG and TmDD during thermal annealing. With the high conductivity and good wetting on the active layer, PEDOT:PSS mixed with PEG-TmDD is used as the top electrode for organic solar cells. The cells exhibit a fill factor of 60% and a power conversion efficiency of 4.1% using poly(3-hexylthiophene):indene-C60 bis-adduct as the active layer. The results indicate that the new formulation of PEDOT:PSS mixed with PEG-TmDD is suitable for preparing a top electrode for vacuum-free organic solar cells. (C) 2015 Elsevier B.V. All rights reserved.