An unconventional electrochemical/solid-state-device integrated system: an electrochemical sensor based on the PCPDTBT polaronic state

This work presents an unconventional device designed <i>via</i> integration of an electrochemical cell and a solid-state circuitry resembling a triode-like configuration, referred to as an electrochemical transistor-like device. In our experimental setup, an organic semiconductor, poly[2,6-(4,4-bis-(2-ethylhexyl)-4<i>H</i>-cyclopenta[2,1-<i>b</i>;3,4-<i>b</i>']dithiophene)-<i>alt</i>-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), serves both as the working electrode (WE) and as a "grid". "Gating" <i>via</i> the grid is established by applying suitable electrochemical polarization to the polymer, exploiting a conventional three electrode electrochemical cell, which is placed directly on top of a device featuring three gold pads. The conductivity (doping) of PCPDTBT is controlled by application of a suitable potential, <i>via</i> the electrochemical cell. The conduction is probed <i>via</i> impedance measurement (electrochemical impedance spectroscopy, EIS): impedance absolute magnitude |<i>Z</i>| and phase <i>ϕ</i> are recorded as a function of time at constant frequency, in the potentiostatic regime. The conductivity is shown to be due to the polaronic state induced by the application of an external potential (in the oxidation regime), evidenced from the infrared (IR) spectra recorded "<i>in situ</i>"/"<i>in operando</i>" (attenuated total reflection, ATR, mode).