In this present work, isomers like 2- and 4-Mercapto pyridine were used as dopants (additives) in Poly (ethylene oxide) based polymer electrolyte and their effects in dye-sensitized solar cells (DSC) have been investigated. Due to the coordinating and plasticizing effects of Mercapto pyridine, enhanced ionic conductivity and reduced crystallinity of PEO polymer electrolyte accompanied by a better penetration of the same into the dye coated nanocrystalline TiO2 in order to have better performances were achieved. The 2-Mercapto pyridine doped PEO (E) shows comparatively better performance than 4-Mercapto pyridine doped one (F), is due to the fact that the pi-electron donicity of 2-Mercapto pyridine is greater. These results suggests that the electron donating capacity of 2-Mercapto pyridine and 4-Mercapto pyridine would influence the interaction of nanocrystalline TiO2 electrode and I-/I3- redox couple leading to radical changes in the cell performance. (C) 2011 Elsevier Ltd. All rights reserved.