Scalable Fabrication of Polyethylenimine (PEI) Doped Laser-Induced Graphene (LIG) Inks

Laser-induced graphene (LIG) is a scalable and cost-effective approach to fabricating carbon-based conductive materials for next-generation flexible electronics. Here, we report the synthesis of LIG by CO₂ laser engraving of polyimide (PI) films, followed by doping with polyethylenimine (PEI). LIG powder was dispersed in a terpineol-ethanol-ethyl cellulose mixture, doped with 21.5 wt % PEI, and deposited as a thick film on a glass substrate using stencil-assisted application. Electrical conductivity measurements showed an increase from ∼20.8 S/m for LIG-only ink to 40 S/m after PEI doping, representing nearly a 2-fold enhancement attributed to increased electron carrier density and a Fermi level shift toward n-type behavior. Comprehensive characterization was performed to assess structural, morphological, and chemical modifications induced by doping. Scanning Electron Microscopy (SEM) confirmed the preservation of a porous, wrinkled graphene-like morphology. Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) showed the successful incorporation of nitrogen. Raman spectroscopy revealed increased defect density and a Fermi level shift characteristic of n-type doping, while X-ray Diffraction (XRD) analysis showed reduced crystallinity and the formation of an amorphous phase. This work demonstrates that PEI not only modifies LIG chemically but also provides structural versatility, highlighting its potential for integration into real-world applications such as flexible and printed electronics. The combination of laser-assisted synthesis and polymer doping offers a practical route to the development of carbon-based materials.