Enhancing the molecular cooperativity of polyvinyl butyral using liquid additives.

The role of acetonitrile and methoxypropionitrile, as accelerators of relaxation dynamics of polyvinyl butyral (PVB), was investigated in polymer/additive mixtures. The aim was to improve the ionic mobility of PVB-based solid electrolytes to be used in solid dye-sensitized solar cells. Mechanical and dielectric relaxation measurements revealed that both the additives cause a growing intermolecular cooperativity, mainly driven by bridges formed through additive molecules, which influence both short- and long-scale segmental motions and also favor the ion dynamics in PVB/additive/electrolyte systems. The room temperature ionic conductivity $\sigma_{rt}$ exhibits large changes from $6.4 \times 10^{-14}$ S/m in dry PVB, through $1.5 \times 10^{-8}$ S/m in PVB/LiI, to $2.45 \times 10^{-5}$ S/m in PVB/MPN/LiI.