“…0.15 M and 0. 30 For the mesoporous TiO2 layer, the TiO2 paste was prepared with TiO2 powder (Aerosil, P-25) with poly(ethylene glycol) (Nacalai tesque, PEG #20000) in ultrapure water [26]. The solution was mixed with acetylacetone (Wako Pure Chemical Industries, 10 μL) and triton X-100 (Sigma Aldrich, 5 μL) for 30 min, and was left for 12 h to suppress the bubble in the solution.…”