(a) Device structure of the MAPbI₃ PD. (b) Photocurrent and dark current of the MAPbI₃, and the photocurrent of the reference photovoltaic device, which has a structure of ITO/PEDOT:PSS/MAPbI₃/PCBM/C60/BCP/Al. (c) Energy diagram of the MAPbI₃ PD at reverse bias under illumination.^[31] (d) Device structure of perovskite–graphene hybrid PDs. (e) The responsivity and EQE versus light intensity relationships for the graphene–perovskite and graphene–perovskite–gold nanoparticle (Au-NP) devices. (f) Schematic of generation, diffusion, and transfer of photo-induced carriers in the perovskite layer with and without the influence of Au-NPs.^[37]