Influence of doping anions on structure and properties of electro-polymerized polypyrrole counter electrodes for use in dye-sensitized solar cells

The nature of doping anions in polymerization solution has great influences on structure and properties of electro-polymerized polypyrrole (PPy) films and, thereby, on the electrocatalytic activity for I-/I-3(-) redox reaction and accordingly the performance of dye-sensitized solar cells (DSSCs) based on PPy counter electrodes (CEs). The ions of chloride (Cl-), sulfate (SO42-), p-toluene sulfonate (TsO-), and dodecyl benzene sulfonate (DBS-) have been used as counter anions to prepare PPy films as CEs in the DSSCs. Compared with inorganic anions (Cl- and SO42-), the organic ones (TsO- and DBS-) afford more delocalized polarons. Moreover, PPy-DBS- films have the most fibrous or porous structure. Thus, PPy -DSB- has plenty of electrocatalytic active sites and high electric conductivity and, thereby, high electrocatalytic activity for I-/I-3(-) redox reaction. Due to the synergistic effects of fibrous/porous structure, high conductivity and low interfacial charge transfer impedance, PPy-DBS- CE based DSSCs show the best photovoltaic conversion efficiency up to 5.40%, reaching 88% of the DSSCs based on Pt CE. Our results indicate that PPy thin films are promising candidates to replace Pt as the CEs for DSSCs, especially for the future flexible devices. (C) 2013 Elsevier B.V. All rights reserved.