Abstract
Flexible dye-sensitized solar cells have been attracted considerable attention due to their advantage of low production cost, widely applications, and feasibility of roll to roll mass production. Compared with plastic substrate, metal foil can withstand high sintering temperature to promote the interconnection between TiO2 particles and reduce internal resistance. However, the formation of metal oxide and 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 TiN and TiN/Ti barriers on stainless steel substrate and then assemble flexible dye-sensitized solar cells to investigate the performance and long-term stability. XRD results shows the single-layered TiN barrier exhibits random orientation, whereas the preferred orientation of the deposited TiN is changed to (111) prefeered orientation in the bi-layer TiN/Ti specimens due to the similar atomic packing between TiN (111) and Ti (002). The surface roughness of single-layered TiN and bi-layer TiN/Ti barrier are 5.58 nm and 8.2 nm respectively. In addition, both two barriers have high packing factor of 0.8 and grain size less than 25nm. The results of potentiodynamic polarization scan and EIS indicate both TiN and TiN/Ti barriers can effectively protect the metal substrate from the corrosive medium. Introducing a Ti interlayer has been found to further decrease the corrosion current density by an order of magnitude; however, bilayer Ti/TiN layer increase the sheet resistance by 230 % In DSCs aspect, The TiN/SS DSCs show 23% better initial performance than SS DSCs. The enhancement of Jsc was mainly due to the fact that TiN thin films provide rougher surface than bare SS substrate, leading to higher dye-loading amount. The results of EIS analysis indicate that TiN thin film can effectively reduce the resistance between TiO2 layer and photo-electrode substrate by inhibiting Fe2O3 formation during sintering process. In addition, TiN/SS DSCs perform excellent long term stability compared with SS DSCs. It was found that the cell maintained ca. 70% of overall conversion efficiency compared with their 24 h-state after 1010 hours aging.