Unprecedented flexibility of in-situ layer-by-layer stacked graphene with ultralow sheet resistance

Although graphene has been extensively studied as a candidate transparent conducting electrode (TCE) material for next-generation flexible devices, transferred large-scale graphene inevitably suffers from wrinkles, ripples, and metallic residues, which significantly lowers its quality by increasing its resistance and reducing its flexibility under tensile strain. As a result, many studies have looked to decrease the sheet resistance and increase the flexibility of graphene, but the complicated fabrication processes and high costs involved are barriers to commercialization. In the present study, 4 in. scale monolayered graphene and layer-by-layer stacked graphene that do not require a transfer process were designed to exhibit high flexibility and ultra-low sheet resistance. Three-layered stacked graphene film grown in situ on a polyethylene terephthalate substrate had an ultra-low sheet resistance of similar to 16 Omega sq(-1) at an optical transmittance of similar to 93% and superior flexibility for 104 cycles under a tensile strain of 5%. However, the plastic deformation of the PET substrate considerably reduced the flexibility of the monolayered graphene. In contrast, monolayered graphene on polydimethylsiloxane, which did not undergo plastic deformation, exhibited unprecedented flexibility at a static tensile strain of 15% (radius of curvature: 0.6 mm) and for 3 x 104 bending cycles under a tensile strain of 11% (radius of curvature: 0.9 mm). This study provides an effective approach for the fabrication of TCEs for use in foldable electronic devices. (c) 2021 Elsevier Ltd. All rights reserved.