Comparison of Photoresponse of Laser-Induced Graphene Photodetectors Fabricated with Intrinsic Laser-Generation and Solution-Processed Palladium Nanoparticles

Abstract

Photodetectors convert incident light into electrical signals, supporting sensing, imaging, and optical communication. Laser-induced graphene (LIG), formed by CO₂-laser photothermal conversion of polymer films, is a promising photodetector material due to its porous, light-trapping structure and high electrical conductivity. Incorporating metallic nanoparticles (MNPs) into the LIG structure can enhance photoresponsivity via plasmon-assisted light absorption and hot-electron transfer at the metal-graphene interface, leading to improved photoresponsivity. Pd nanoparticles can be generated using a one-step laser process, in which Pd ligands dissolved in a polymer of intrinsic microporosity (PIM) are reduced synchronously with graphene formation, or solution-deposited onto pre-formed LIG. These routes have not been directly compared before. We hypothesized that PdNP-embedded LIG would outperform solution processing, since PIM miscibility with inorganic materials should distribute nanoparticles evenly, improve graphene contact, and avoid solvent-induced degradation seen in solution processing. We fabricated composites via both methods, applied a bias voltage, and illuminated devices at 480 nm, recording photocurrent over three 10-second on/off cycles per device, alongside unmodified LIG as a baseline. Contrary to our hypothesis, solution-deposited PdNP-LIG showed the largest photocurrent swing, 8.0-fold (807.8%) greater than the best intrinsic formulation, 30% PIM PdNP. Solution-deposited PdNP-LIG was also 21.1-fold (2107.3%) greater than unmodified LIG. Surface-deposited nanoparticles thus generated a substantially stronger plasmon-assisted photoresponse than PdNP-embedded ones, opposite our prediction, suggesting direct surface exposure matters more than embedded contact points. An important variable that may impact the results is that PIM is a different polymer than Polyimide (PI), each having different graphene morphology, electrical characteristics, as well as the graphene pore structure, possibly impacting photoresponsivity. Future work will compare Pd with Au nanoparticles fabricated using the same polymer matrix so that differences in graphene morphology and pore structure are minimized, allowing the effect of metal type on photoresponsivity to be isolated and recorded.