Exfoliated graphene-alkaline lignin-PEDOT: PSS composite as a transparent conductive electrode

In this work, we report a graphene-alkaline lignin-poly(3,4-ethylenedioxythiophene) polystyrene sulfonate composite as a transparent conductive electrode for indium tin oxide-free optoelectronic devices. The composite was prepared by dispersing exfoliated graphene-alkaline lignin into aqueous poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. The effect of graphene concentration on the electrical and optical properties of graphene-alkaline lignin-poly(3,4- ethylenedioxythiophene) polystyrene sulfonate was studied. The graphene-alkaline lignin-poly(3,4- ethylenedioxythiophene) polystyrene sulfonate thin films exhibit excellent electrical conductivity and high transparency properties. The electrical conductivity is further increased by 1.9 ± 0.01 × 103 times when graphene content was augmented in the composites; however, the optical transparency was reduced due to the high optical absorbance of graphene. In this condition, the conductivity and optical transparency are as high as (4.19 ± 0.01) × 103 S/cm and 94.2%, respectively. This achievement is attributed to the organization of higher ordered network between conductive exfoliated graphene and poly(3,4-ethylenedioxythiophene) chains that induced a better conducting channel for charge transportation. The poly(3,4-ethylenedioxythiophene) chains act as a bridge connecting the graphene flakes, which, in turn, facilitate the movement of hole charges between them.