Transparent Conductors from Carbon Nanotubes LBL-Assembled with Polymer Dopant with π−π Electron Transfer

Abstract

Single-walled carbon nanotube (SWNT) and other carbon-based coatings are being considered as replacements for indium tin oxide (ITO). The problems of transparent conductors (TCs) coatings from SWNT and similar materials include poor mechanical properties, high roughness, low temperature resilience, and fast loss of conductivity. The simultaneous realization of these desirable characteristics can be achieved using high structural control of layer-by-layer (LBL) deposition, which is demonstrated by the assembly of hydroethyl cellulose (HOCS) and sulfonated polyetheretherketone (SPEEK)-SWNTs. A new type of SWNT doping based on electron transfer from valence bands of nanotubes to unoccupied levels of SPEEK through π−π interactions was identified for this system. It leads to a conductivity of 1.1 × 10⁵ S/m at 66 wt % loadings of SWNT. This is better than other polymer/SWNT composites and translates into surface conductivity of 920 Ω/◻ and transmittance of 86.7% at 550 nm. The prepared LBL films also revealed unusually high temperature resilience up to 500 °C, and low roughness of 3.5 nm (ITO glass −2.4 nm). Tensile modulus, ultimate strength, and toughness of such coatings are 13 ± 2 GPa, 366 ± 35 MPa, and 8 ± 3 kJ/m³, respectively, and exceed corresponding parameters of all similar TCs. The cumulative figure of merit, ∏_TC, which included the critical failure strain relevant for flexible electronics, was ∏_TC = 0.022 and should be compared to ∏_TC = 0.006 for commercial ITO. Further optimization is possible using stratified nanoscale coatings and improved doping from the macromolecular LBL components.