Fig. 5.

Cross-sectional schematic and SEM images of perovskite cell with integral monolayer h-BN and graphene aerogel. a Schematic of a graded bandgap perovskite solar cell. Gallium nitride (GaN), monolayer hexagonal boron nitride (h-BN), and graphene aerogel (GA) are key components of the high-efficiency cell architecture. b Cross-sectional SEM image of a representative perovskite device. The division between perovskite layers and the monolayer h-BN is not visible in this SEM image. The dashed lines indicate the approximate location of the perovskite layers and the monolayer h-BN as a guide to the eye. The location of perovskite layers and monolayer h-BN is extracted from the related EDAX analysis. Thickness of the CH₃NH₃SnI₃ layer is 150 nm and that of the CH₃NH_3PbI_3−xBr_x is 300 nm. Scale bar, 200 nm [29]