Novel Hybrid 1-D Structure of PEDOT/TiO2 Nanotubes As the Pt-Free Catalyst of Counter Electrodes in Dye-Sensitized Solar Cells

Due to its outstanding electrocatalytic ability and reliable stability under severe circumstances, Pt is one of promising catalysts in electrochemical applications. However, cost issue and delicate process is inevitable for this kind of precious metals. How to provide a dependable material is an interesting issue. Hence, in this study, novel one-dimensional (1-D) hybrid structure of poly(3,4-ethylenedioxythiophene) (PEDOT) supported with TiO₂ nanotubes (PEDOT/TNTs) were successfully synthesized and further applied as catalysts of counter electrodes (CEs) for dye–sensitized solar cells (DSSCs). PEDOT/TNTs were formed with electropolymerization of 3,4-ethylenedioxythiophene onto TiO₂ nanotubes (TNTs) by the pulse current process, in which TNTs were obtained by anodization of Ti foils. After optimizing the sintering temperature of TNTs and electropolymerizing charge density of PEDOT, a high solar–to–electricity conversion efficiency (η) of 8.82% is achieved for a DSSC containing the CE of PEDOT/TNTs, with the optimized sintering temperature of 400 ^oC for TNTs and electropolymerizing charge density of 400 mC/cm² for PEDOT deposited onto TNTs (PEDOT/TNTs-400 mC/cm²); a η is higher than those of the cells with the CEs of flat PEDOT (6.50%) and Pt (8.24%). Cyclic voltammetry (CV), symmetric electrochemical impedance spectra (s–EIS) and Tafel polarization plots reveal that the highest h of the cell with PEDOT/TNTs is due to the higher electrocatalytic ability of the CE for the reduction of triiodide ions (I₃^–) and lower charge transfer resistance (R_ct) at the interface between the CE and the electrolyte. Incident photon–to–current conversion efficiency (IPCE) spectra are used to substantiate the explanations on the photovoltaic parameters of the cells.