(color online) (a) Schematic architecture of the investigated device consisting of FTO as a transparent substrate, a compact TiO₂ layer, a mesoporous TiO₂ layer, an Al₂O₃ layer coated with SWCNT added graphite/carbon black CE, (b) cross-section SEM image of a mesoscopic perovskite solar cell. Reprinted from Ref. [32]. (c) Photo of freestanding CNT film lifted by tweezers to transfer onto other substrates. (d) Schematic of CH₃NH₃PbI₃ perovskite solar cell with CNT film electrode. (e) Top view SEM images of CH₃NH₃PbI₃ perovskite substrate before and (f) after CNT transfer. (g) Tilted SEM image of CH₃NH₃PbI₃ perovskite substrate (blue) partly covered by CNT film (purple). Reprinted from Ref. [66].