Principles for fabricating moisture barrier films via stacked Janus graphene layers

The excellent impermeability makes graphene film an ideal candidate for thin film encapsulation technology. However, current chemical vapor deposition (CVD) graphene-based barrier films can not provide sufficient moisture barrier performance, suggesting a lack of understanding in mechanism that dominates water diffusion in/through graphene stacks. Herein, we fabricate large-area graphene barrier films with a record-low water vapor transmission rate (WVTR) of 5 × 10^-5g/(m²·day), two orders of magnitude lower than previous works, in which two stacked Janus graphene films are intercalated by toluidine blue O (TBO) sub-monolayer: one side of graphene is decorated with fluorine- and oxygen-containing groups to allow crack-free transfer, while the other side is functionalized with hydroxyl groups to trap water. The intercalated TBO further blocks water transport due to a strong water-TBO interaction. Our work opens a route for surface/interface engineering of CVD graphene and promises its exciting future in the applications for advanced packaging.