In order to examine the surface passivation effects on solar cell performance, the surface of the porous titania was treated with dilute solutions with various concentrations, such as 0.2, 1, and 5 mM. The different concentrations correspond to points A, B, and C in Fig. 3, where 150 to 200, 100 to 125, and of were absorbed on the porous titania surface. After the surface treatment of the titania layer with a dilute solution, the mixed solution of and MAI was spin-coated on the porous titania layer to form a perovskite layer (Perov Pb). The photovoltaic performances for these solar cells are summarized in Table 1, in which the performance for a Perov Pb solar cell without any surface pretreatment is also included. It is observed that the photovoltaic performances, namely, and , increased with an increase in the concentration of passivation from 0.2 to 5 mM as shown in A, B, and C in Fig. 3. These results demonstrate that the photovoltaic performances are improved by controlling the titania–perovskite interfaces (passivation effect).