| Summary: | Supercapacitors demonstrate substantial improvement in charge storage capability compared to the conventional capacitors. With the emergence of printed electron- ics such as RFID tags, smart cards, electronic paper, and wearable electronics, printed energy storage devices are desirable. Therefore, a flexible and printable supercapacitor with a PEDOT:PSS electrode is fabricated with inkjet micropatterning technology. Electroanalytical measurement techniques are employed to characterize the performance of the printed supercapacitor. It has been found that addition of the surfactant (Triton X-100) increases the porosity of the PE- DOT:PSS electrode. A volume capacitance of 9.36 F/cm₃ (adding surfactant) and 9.09 F/cm₃ (without adding surfactant) are measured with cyclic voltammetry. The two devices have different capacitor charging times, e.g., 50.46 s for electrode added surfactant and 112.9 s for the electrode without adding surfactant.
In order to investigate the rate limiting factors of capacitor charging, electro- chemical impedance measurements and equivalent circuit modelling is utilized. Instead of using a constant phase element (CPE), a multiple time constant model is proposed in order to explain the physical origin of the distributed time constant behaviour. Thickness variation of the PEDOT:PSS electrode is assumed as a primary reason for the distributed time constants and thus actual thickness variation is incorporated in the modelling. Data fitting with the measured impedance are consistent with this assumption. However. it also has been found that there are more factors distributing capacitances than just variations in thickness. A lognormal distribution function (LNDF) is utilized in order to further investigate the relationship between the distributed capacitance and the capacitor charging. It is found that the capacitance distribution likely influence the charging.
Previous experimental results demonstrate that the distributed capacitance is the physical cause of the distributed time constant behaviour in electrochemical impedance measurement. However, this is the first analytical report proving the relationship between the distributed time constant behaviour and a thickness de- pendent capacitance distribution.
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