Highly Conductive and Transparent Large-Area Bilayer Graphene Realized by MoCl5 Intercalation

Bilayer graphene (BLG) comprises a 2D nanospace sandwiched by two parallel graphene sheets that can be used to intercalate molecules or ions for attaining novel functionalities. However, intercalation is mostly demonstrated with small, exfoliated graphene flakes. This study demonstrates intercalation of molybdenum chloride (MoCl₅) into a large-area, uniform BLG sheet, which is grown by chemical vapor deposition (CVD). This study reveals that the degree of MoCl₅ intercalation strongly depends on the stacking order of the graphene; twist-stacked graphene shows a much higher degree of intercalation than AB-stacked. Density functional theory calculations suggest that weak interlayer coupling in the twist-stacked graphene contributes to the effective intercalation. By selectively synthesizing twist-rich BLG films through control of the CVD conditions, low sheet resistance (83 Ω ▫⁻¹) is realized after MoCl₅ intercalation, while maintaining high optical transmittance (≈95%). The low sheet resistance state is relatively stable in air for more than three months. Furthermore, the intercalated BLG film is applied to organic solar cells, realizing a high power conversion efficiency.

Intercalation of MoCl₅ into large-area bilayer graphene (BLG) grown by chemical vapor deposition is performed. Twist stacking gives a much higher degree of MoCl₅ intercalation than AB stacking. A low sheet resistance with high optical transmittance is obtained by using twist-rich BLG. A transparent electrode suitable for use in organic solar cells is developed from this intercalated bilayer.

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