Suppressed Interdiffusion and Degradation in Flexible and Transparent Metal Electrode-Based Perovskite Solar Cells with a Graphene Interlayer.

Metal-based transparent conductive electrodes (TCEs) are attractive candidates for application in indium tin oxide (ITO)-free solar cells due to their excellent electrical conductivity and cost effectiveness. In perovskite solar cells (PSCs), metal-induced degradation with the perovskite layer leads to various detrimental effects, deteriorating the device performance and stability. Here, we introduce a novel flexible hybrid TCE consisting of a Cu grid-embedded polyimide film and a graphene capping layer, named GCEP, which exhibits excellent mechanical and chemical stability as well as desirable optoelectrical properties. We demonstrated the critical role of graphene as a protection layer to prevent metal-induced degradation and halide diffusion between the electrode and perovskite layer; the performance of the flexible PSCs fabricated with GCEP was comparable to that of their rigid ITO-based counterparts and also exhibited outstanding mechanical and chemical stability. This work provides an effective strategy to design mechanically and chemically robust ITO-free metal-assisted TCE platforms in PSCs.