Fig. 7. (a) The structural diagram of the three perovskite devices, and the J–V curve of the corresponding devices are at 1000 lux illumination. Reproduced from ref. 217 with permission from the [Wiley-VCH], copyright [2018]. (b) Schematic diagram of the structure of mesoporous TiO₂ prepared by different methods and the J–V curve of the optimal device. Reproduced from ref. 223 with permission from the [Elsevier], copyright [2016]. (c) Schematic diagram of the device structure fabricated by SnO₂ with MgO treatment and the J–V curves of the corresponding devices under different light conditions. Reproduced from ref. 227 with permission from the [Elsevier], copyright [2018].