Fig. S3(a)–(c) shows SEM photos of TiO2 paintings by screen-coating the paste-1 (small porous TiO2 spheres) and paste-3(nanoparticles) on FTO glass substrates. Fig. S3(a) is the single-layer TiO2 sphere coating made of paste-1, with the magnification picture being shown in left-corner. It can be seen that this TiO2 coating consists of perfect TiO2 spheres, which was not destroyed during the paste preparation. These spheres compact together tightly and connected well from each other, so this should be beneficial for the electron transport.