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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 ( ε r * = ε r ′ − j ε r ″ ) of PEDOT:PSS layers perpendicular to the layer plane in the 10−2–106 Hz range by combining data from the reactive energy estimations and electrochemical impedance spectroscopy, and discover that: ε r ′ at <1 Hz is ultra-high (∼106) decreasing with frequency to ∼5 at 106 Hz; the experimental data fit the Cole-Cole dielectric relaxation model by considering multiple relaxation mechanisms; PEDOT:PSS polarizes nonlinearly and ε r ′ increases with the intensity of the applied external field; low frequency ε 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 ε r ′ at 1.0 kHz is three orders of magnitude higher than the vertical ε r ′ ; and that the ε 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. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylenedioxythiophen):polystyrene sulfonate (PEDOT:PSS) is a conductive polymer composite commonly used as a hole-transporting material in various optoelectronic devices. Here, we show that both real and imaginary components of the impedance of a micrometer-thick drop-cast PEDOT:PSS layer measured perpendicular to the layer plane are strongly nonlinear and vary with both amplitude and frequency of the externally applied field. In thinner layers, the impedance approaches linearity; impedances of layers thinner than 100 nm are almost linear within the investigated field and frequency ranges. Impedance nonlinearity is more profound at low-frequencies and almost disappears above 1 kHz. The experimental results are described based on the complex polarization mechanisms prevailing at low-frequencies due to the lazy dynamics of the massive interfacial dipoles formed between PEDOT and PSS chains. The nonlinear impedance of a 2.0 μm-thick layer is utilized for the design and fabrication of a harmonic generator, a frequency adder, and a up/down converter operating at very low frequencies. Operations of a micrometer-thick drop-cast dot of PEDOT:PSS, as a second and third harmonic generator and a passive intermodulator in the frequency range of biological signals are demonstrated. Other polymer composites with large interfacial dipoles are expected to own similar properties. [ABSTRACT FROM AUTHOR]