The complex permittivity of PEDOT:PSS

High permittivity materials are required for efficient organic photovoltaic devices, and the addition of the conjugated polymer composite poly(3,4-ethylenedioxythiophen) polystyrene sulfonate (PEDOT:PSS) to dielectric polymers has been shown to significantly heighten their permittivity. The permittivity of PEDOT:PSS at the optical and microwave frequencies has been investigated, but PEDOT:PSS layers are mainly used for low-frequency device applications, where accurate dielectric property measurements are hindered by their high electrical conductivity and the problems arising from the metal-polymer interfaces. Here, we determine the complex relative permittivity (E*(r) = E'(r) - jE'' (r) ) of PEDOT:PSS layers perpendicular to the layer plane in the 10(-2)-10(6) Hz range by combining data from the reactive energy estimations and electrochemical impedance spectroscopy, and discover that: E'(r) at <1 Hz is ultra-high (-106) decreasing with frequency to similar to 5 at 10(6) Hz; the experimental data fit the Cole-Cole dielectric relaxation model by considering multiple relaxation mechanisms; PEDOT:PSS polarizes nonlinearly and E'(r) increases with the intensity of the applied external field; low frequency E'(r) increases with both thickness and temperature of the layer, opposite trend of temperature-dependence prevails at >103 Hz; the dielectric properties of PEDOT:PSS are highly anisotropic and the in-plane E'(r) at 1.0 kHz is three orders of magnitude higher than the vertical E'(r); and that the E'' (r) decreases proportional to the reciprocal of frequency (1/f). The latter finding provides an explanation for the ubiquitous pink noise accompanying signals transmitted through organic conductor links. The described methodology can be adopted for investigations on other conjugated polymers.