Graphene interfacial diffusion barrier between CuSCN and Au layers for stable perovskite solar cells

Perovskite solar cells (PSCs) have rapidly achieved a remarkable power conversion efficiency (PCE). However, the inherent instability of components has impeded industrialization. Here we employed atomically-thin impermeable graphene (3 layers) as an interfacial barrier for moisture, I⁻ ion, and Au diffusion. A new graphene transfer method was developed, and the position was carefully optimized between the CuSCN and Au electrode in a full cell considering the band alignment of cell components. There was a negligible change in maximum PCE (15.2–15.8%) with the incorporation of graphene due to the high hole mobility of graphene. The moisture intrusion was significantly reduced under 85% relative humidity (RH) for 3 weeks, suppressing PbI₂ formation. The graphene barrier maintained >94% of initial PCE under 50% RH for 30 days. It mostly inhibited I⁻ ion migration and perfectly blocked Au diffusion between the perovskite and Au electrode, allowing reversible recovery of electrical power during 3 continuous illumination/dark cycles (12 h each) with a positive bias. A further improvement in the graphene transfer method may enable a perfect single-layer graphene barrier, without compromising the average PCE of multiple devices.