Nonlinear impedance of a micrometer-thick layer of poly(3,4-ethylenedioxythiophen):polystyrene sulfonate

Abstract

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.