The performance of DSSCs can be improved if iodine species can be pre-stored in the polymer counter electrodes (CEs) since the I-/I-3(-) redox couple is usually used as the mediator in electrolyte for DSSCs. In this work, such porous polypyrrole (PPy) CEs have been successfully synthesized by electrochemical method. Detailed mechanism about the electro-polymerization and film growth has been investigated both experimentally and theoretically. The influence of iodine species pre-stored in the film during polymerization on the properties of resultant PPy CEs (such as porous structure, doping state, and electrocatalytic activity) and, thereby, the device performance has been studied thoroughly. We envision that the results may help to facilitate the research and development of the polymer-based CEs used in DSSCs. (C) 2014 Elsevier B.V. All rights reserved.