Li et al. established a linear relationship between VPP PEDOT film thickness and transmittance for thicknesses in the range of 10 to 50 nm. A control PEDOT film was analyzed, and the transmittance in the visible range was measured to be 93.7%. This value was used with the published data to determine an approximate thickness of 23 nm. The thickness of a control graphene film was determined using the principle established by Nair et al. that each layer of graphene reduces the transmittance of white light by 2.3%. Our graphene film exhibited a transmittance of 87.6% over the visible range, corresponding to a reduction of 12.4%. This reduction indicates the presence of 5 to 6 layered graphene, agreeing with the 2D peak shoulder intensity calculations. The interlayer spacing of graphite is ~0.335 nm , so the graphene film thickness was approximately 2 nm. This information provided a likely range of composite film thickness. Figure . A) XRD spectra of a 300 µm graphene film (blue), a PEDOT-graphene film (green), and an acid-treated PEDOT-graphene film, also referred to as a doped film (red). B) SEM image of the PEDOT-graphene film. C) Transmittance of a film made of 300 µm flake natural graphite and transmittance of a PEDOT-graphene film produced from 300 µm flake graphite. D) XPS analysis of the Si 2p region. The plot displays experimental data (black circles) and fitted curves, originally deconvoluted with CasaXPS. The total fit (black solid line) is deconvoluted into two components: SiO₂ (blue dashed line) and highly oxidized Si (green dashed line).