Ultrafast PEDOT:PSS/H2 SO4 Electrical Double Layer Capacitors: Comparison with Polyaniline Pseudocapacitors.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is one of the most widely studied conductive polymers, owing to its excellent electrical, optical, and mechanical properties, with various applications such as organic electrochemical transistors, electrochromics, and flexible/stretchable supercapacitors. The charging mechanism of PEDOT:PSS supercapacitors has been traditionally believed to be faradaic, which involves the transfer of charge across the electrode/electrolyte interface. In the present work, however, robust experimental evidence suggests that the PEDOT:PSS supercapacitors mainly store and deliver charge nonfaradaically. The various electrochemical properties of PEDOT:PSS electrical double layer capacitors (EDLCs) are clearly distinguishable from those of polyaniline (PANI) pseudocapacitors, which store charge faradaically. Owing to the nonfaradaic mechanism, the frequency response of PEDOT:PSS supercapacitors is comparable to that of state-of-the-art ultrafast EDLCs with carbon-based electrodes, making them suitable for high-frequency applications such as 60 Hz AC line filtering. This result is of great importance for the fundamental understanding of the charging mechanism of mixed ionic-electronic conducting polymers, such as PEDOT:PSS, and is expected to contribute to the development of various electrochemical devices based on this type of material.

Ultralow voltage operation of biologically assembled all carbon nanotube nanomesh transistors with ion-gel gate dielectrics.

The demonstration of field-effect transistors (FETs) based entirely on single-walled carbon nanotubes (SWNTs) would enable the fabrication of high-on-current, flexible, transparent and stretchable devices owing to the excellent electrical, optical, and mechanical properties of SWNTs. Fabricating all-SWNT-based FETs via simple solution process, at room temperature and without using lithography and vacuum process could further broaden the applicability of all-SWNT-FETs. In this work, we report on biologically assembled all SWNT-based transistors and demonstrate that ion-gel-gated network structures of unsorted SWNTs assembled using a biological template material enabled operation of SWNT-based transistors at a very low voltage. The compatibility of the biologically assembled SWNT networks with ion gel dielectrics and the large capacitance of both the three-dimensional channel networks and the ion gel allowed an ultralow operation voltage. The all-SWNT-based FETs showed an I on /I off value of >102, an on-current density per channel width of 2.16 × 10-4 A/mm at VDS = 0.4 V, and a field-effect hole mobility of 1.12 cm2/V · s in addition to the low operation voltage of <-0.5 V. We envision that our work suggests a solution-based simple and low-cost approach to realizing all-carbon-based FETs for low voltage operation and flexible applications.