Highly transparent TiO2 nanowires as charge-balancing layers for assembling electrochromic devices: effect of thickness on electrode potentials and electrochromic performance.

TiO2 nanowires with high transparency and good ion storage capacity were explored as the charge-balancing layers for assembling electrochromic devices (ECDs). Increase thickness of TiO2 nanowires layer lowers the driving potential of the entire ECDs accompanied with reduced potential at the EC layer electrode, which further leads to decreased optical contrast and switching speed of the ECDs. Meanwhile, it can be found that the EC layer electrodes possess larger charge densities than those of TiO2 nanowire electrodes during the electrochemical redox process of these ECDs. However, the intrinsic injection and extraction charge densities of each single electrode are similar, which appears that the intrinsic charge balance of EC layer and TiO2 nanowires electrodes play more important role in the cycling stability of the ECDs. ECD with an optimum thickness of the TiO2 nanowires layer exhibits good electrochromic properties in term of high optical contrast (∼45%), fast switching speed (3.23 s) and excellent cycling stability (which has nearly no decay after 5000 cycles). This study explores the effects of thickness of TiO2 Nanowires layer on electrode potentials and electrochromic properties of electrochromic devices (ECDs), providing a potentially new direction for the preparation of ECDs with good integrated performance.