Flexible Semitransparent MXene Thin-Film Heaters Enhanced by Conducting Polymer Percolation Network

Two-dimensional transition metal carbides and nitrides (MXenes) are promising candidates for flexible thin-film heaters owing to their high electrical conductivity, mechanical pliability, and solution processability. However, achieving both optical transparency and efficient Joule heating in flexible MXene films remains challenging due to the intrinsic trade-off between film thickness and light transmittance. Here, we report flexible, semitransparent MXene thin-film heaters enabled by a percolated conducting polymer network of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS). The strong aqueous compatibility between PEDOT:PSS and MXene allows homogeneous codispersion and facile film formation via spin-coating. Post-treatment with trifluoroacetic acid (TFA) significantly enhances electrical conductivity by inducing structural and compositional reorganization within the composite, reducing the sheet resistance from 1240 ± 117.9 to 129 ± 7.6 Ω sq^-1 while maintaining a visible transmittance of 70.6%. The optimized films fabricated on ultrathin polyethylene naphthalate substrates exhibit excellent electrothermal performance, including a steady-state temperature of 92.2 °C at 10 V, a short heating thermal time constant of 3 s, and robust mechanical flexibility with a bending radius down to 1.7 mm. The heaters also demonstrate stable and uniform operation under repeated cycling. As a proof of concept, an electrically driven thermochromic device is demonstrated, highlighting the potential of PEDOT:PSS/MXene nanocomposites as rapid-response, flexible thin-film heater platforms for transparent and wearable thermal management applications.