Evaluation of defects and current kinetics for aging analysis of PEDOT:PSS based supercapacitors

Abstract Poly (3, 4-ethylene-dioxythiophene) polystyrene sulfonate (PEDOT: PSS) electrodes are readily been used as a prominent research candidate as the supercapacitor's active electrode. The benefits of PEDOT based super-capacitors as a charge storage material are wide i.e. high conductivity, prominent stability, suitable conjugated porous backbone, wider working range, fast redox reaction, optical transparency, and easy processability. While the drawback of PEDOT:PSS shows inhomogeneous electrical and morphological properties that result in poor long term stability and causes the limitation in its shelf-life. This work proposes a significant cause of its degradation (during active and standby modes) and studied the charge level analysis for the very first time. We have fabricated and subsequently characterized with a special focus to evaluate the post-aging (~120 days) charging and discharging nature of the PEDOT:PSS supercapcitor. Thus, the defects present within the PEDOT:PSS interface have been studied to address the less-evaluated problematic area and for better understand the inhomogeneities in view of basic Charge, for improved system-level applications of supercapacitors. Characterizations are performed using Current-Voltage (I-V) analysis with two probe technique using copper contacted anode-cathode. I-V tests are conducted at multiple ambient conditions to inspect the thermal stability and sustainability of the ultra-capacitor. It is found that at rather higher ambient temperatures i.e. >36°C, the charging current was observed to fall and reduced the charge collection mechanism of the said supercapacitor. With the help of Charge-Deep Level Transient Spectroscopy (Q-DLTS), the behavior of charge/discharge in this specific device and the extent of recombination centers was found which is mainly responsible for the degradation of its capacitive operation. The electrochemical characteristics were assessed using Electro-chemical Impedance Spectroscopy (EIS) with Nyquist and Bode plots; describing the internal electrical metrology of the devices. The kinetics of current also provided an insight that higher operating temperatures might limit the device performance. Aging-assisted defects and temperature-dependent kinetics of current have ramifications of the design and process engineers for the potential usage of the supercapacitors in certain systems with specific process requirements.