Measuring optical anisotropy in poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) films with added graphene

• The effect of added graphene on the optical properties of PEDOT:PSS was measured.
• TIR spectroscopy was used for samples too rough or absorbing for ellipsometry.
• Spray-coated PEDOT:PSS films are optically anisotropic, like spin-coated ones.
• Conductivity is greatly increased with added graphene, little effect on anisotropy.

Graphene is a 2D nanomaterial having a great potential for applications in electronics and optoelectronics. Composites of graphene with conducting polymers have shown high performance in practical devices and their solution-processability enables low-cost and high-throughput mass manufacturing using printing techniques. Here we measure the effect of incorporation of graphene into poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) to the optical anisotropy, absorbance and conductivity of the film. Uniaxial anisotropy in PEDOT:PSS films has been thought to be caused by the spin-coating process used in fabrication. We have characterized spray- and spin-coated films using ellipsometry and total internal reflection spectroscopy, the latter especially for films too thick and uneven for ellipsometry, and show that spray-coating, similar to inkjet printing, also produces consistently anisotropic properties even in very thick and uneven films. Possible plasmonic excitations related to graphene are not seen in the films. The optical and electrical anisotropy of graphene/PEDOT:PSS enables routes to high performance devices for electronics, photonics and optoelectronics.

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