In this study, the conductivity of poly (3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) was greatly enhanced by using sodium dodecyl sulfate (SDS) without damaging the fabric substrates. We suggest that blending and dipping methods using SDS which is compatible with natural and synthetic fabrics dramatically increase the conductivity of PEDOT:PSS to as high as 1335 S cm À1. Additionally, a highly stretchable fabric heater with high conductivity was successfully fabricated using SDS-modified PEDOT:PSS. The fabric heaters exhibited reversible electrical behaviour with cyclic loading of a tensile strain even larger than 80%. The increase in resistance with the tensile strain was significantly smaller than the calculated value for a rigid substrate because the fabrics with a weave structure exhibited interfibrillar contact effects with strain. For example, the resistance was increased by a factor of only 2.62 with 80% strain. The Joule heating behaviours of the fabric heaters were demonstrated at several different applied voltages and ambient temperatures, and the heat capacity and convective heat transfer coefficient were 2 J K À1 and 30 W m À2 K À1 , respectively. The results demonstrated that the method suggested in this work is not only efficient for greatly improving the conductivity but also simple and cost-effective for fabricating highly conductive and stretchable fabrics with various e-textile applications.

A room‐temperature HNO3 treatment method is developed that significantly enhances the conductivity of a poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) film, which is one of the most promising transparent conducting materials. The PEDOT:PSS film treated with HNO3 exhibits a conductivity as high as 4100 S cm−1, which is the highest value among reported conductivities achieved by treatments at room temperature. The mechanism of this conductivity enhancement is elucidated by means of electrical, optical, structural, and compositional characterizations of the PEDOT:PSS films. The HNO3 treatment induces phase separation and crystallization in the (100) and (200) directions of PEDOT:PSS through selective removal of the PSS domains. This rearrangement significantly increases the conductivity through an enhancement of the inter‐chain interaction between the conducting polymers. Dye‐sensitized solar cells (DSSCs) that adopt these films as counter electrodes are developed as an example of practical applications. Using the HNO3‐treated PEDOT:PSS films, a power‐conversion efficiency of 8.59% is achieved for Pt/fluorine‐doped tin oxide (FTO)‐free DSSCs. This study demonstrates that a facile HNO3 treatment at room temperature is one of the most promising methods for obtaining highly conductive and transparent PEDOT:PSS films, and it facilitates the commercial use of PEDOT:PSS in next‐generation transparent electrodes.

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