Enhanced corrosion resistance of TiN-coated stainless steels for the application in flexible dye-sensitized solar cells

Metals foils have been increasingly used as alternative substrates for the flexible dye-sensitized solar cells (DSSCs) to overcome the limitations arising from the low sintering-temperature tolerance of the plastic substrates. However, the potential problem of metal corrosion in the iodide-based electrolytes threatens to degrade the performance and long-term stability of the metal-based DSSCs. To resolve this dilemma, we have employed unbalanced magnetron sputtering systems to prepare nanocrystalline TiN and TiN/Ti barriers, with the high packing factors of 0.7-0.8, on the metal substrates. The microstructure and properties of TiN and TiN/Ti barriers were characterized using SEM, XRD, AFM and SIMS. Their corrosion behaviors were evaluated through electrochemical impedance spectroscopy and potentiodynamic polarization in the simulated iodide-based electrolytes environment. The results show more than 78% improvement in reducing the corrosion current density by the deposition of the barrier. The charge transfer behavior occurring in the metal/electrolyte interface is also suppressed by the deposited barriers. Furthermore, because deposited barriers provide a larger surface area for dye adsorption and possess better corrosion protection, the barrier-deposited DSSCs have been demonstrated to attain 2.5 times higher energy conversion efficiency than uncoated DSSC.