P. Zhang, Z. Hu, Y. Wang, Y. Qin, W. Li, and J. Wang, “A Bi-layer Composite Film Based on TiO2 Hollow Spheres, P25, and Multi-walled Carbon Nanotubes for Efficient Photoanode of Dye-sensitized Solar Cell”, Nano-Micro Lett, vol. 8, no. 3, pp. 232-239, Feb. 2016.