Monolayer CVD Graphene Barrier Enhances the Stability of Planar p–i–n Organic–Inorganic Metal Halide Perovskite Solar Cells

The poor environmental stability of hybrid perovskite solar cells (PSCs) remains one of the leading obstacles to their commercialization. Herein, we develop and use, for the first time, an orthogonal solvent-assisted process to transfer sheets of monolayer chemical vapor deposited (CVD) graphene onto the perovskite active layer without causing damage to the perovskite layer. We show that at this location in a standard methylammonium lead iodide PSC stack, the CVD graphene acts as a barrier layer to improve stability by (i) preventing moisture ingress into the perovskite layer and (ii) blocking the diffusion of silver ions from the electrode to the perovskite layer. Upon exposure to humidity for 1 week, unencapsulated devices with a graphene barrier retained 93% of their initial PCE, whereas those devices without a graphene barrier retained only 46%. Similarly, after heat treatment, unencapsulated devices with a graphene barrier showed no decrease in PCE, whereas those without a graphene barrier decreased to ∼75% of their initial PCE. CVD graphene is shown to be a prime candidate for improving the environmental stability of PSCs.