The effect of ammonia concentration on the microstructure and electrochemical properties of NiO nanoflakes array prepared by chemical bath deposition

This paper presents the electrochromic (EC) characteristics of nickel oxide (NiO) nanoflakes array prepared by chemical bath deposition (CBD) method with different ammonia concentration. Prepared NiO films have porous structure with 2-dimensionally networked nanoflake arrays. The addition of aqueous ammonia significantly affects the growth of NiO film. Moreover, appropriate amount addition of aqueous ammonia is important in obtaining a balanced EC performance of NiO films between transmittance modulation and cycling durability. Excess concentration of ammonia cause not only a decrease in the thickness of NiO films but also change the growth direction of flakes. XPS results present that high concentration of ammonia could induce the peak shifting toward the low binding energy, which attributed from initial state effect between nickel and oxygen, which is substituted by nitrogen. The best electrochemical durability at 550 nm was achieved for NiO-25 film with high transmittance modulation (Tbleaching: 86.8% and Tcoloring: 23.4%) and noticeable cycling stability (only 25% decrease after 5000 cycles).