Fabrication of flexible, adhesive, and highly conductive freestanding carbon nanotube films with poly(disulfide) main chains containing a functional polymer for high-performance carbon-based perovskite solar cells

Abstract

Carbon-based thin films with high electrical conductivities have attracted significant attention due to their extensive applications across diverse fields, including solar cells, batteries, high-performance supercapacitors, and nanofiltration devices. Here, we report a simple, cost-effective and scalable approach to fabricate strong, flexible, adhesive, and highly conductive free standing composite thin films of multiwalled carbon nanotubes (MWCNTs) and a functional polymer poly(thioctic acid) [poly(TA)]. The polymer was obtained through dynamic covalent ring-opening-polymerization of thioctic acid (TA) upon heating. A simple strategy involving the grinding of MWCNTs with the functional polymer poly(TA) in optimal proportions forms a dough-like mixture, which on hot-pressing and spreading over a solid substrate provides high quality carbon-films. The unique structure of the polymer, having a dynamic covalent poly-disulfide chain as the backbone and carboxyl side chains as pendants enables strong coupling and ordering of MWCNTs with high packing density for the formation of the conductive film. The film exhibits a high electrical conductivity of 7518 S m⁻¹ with extremely low electrical sheet resistance (2.5 Ω sq⁻¹) at a thickness of about 50 μm. The crack-free uniform morphology of the film, combined with the flexibility and adhesive properties imparted by the polymer enables facile integration with diverse substrates, making it suitable for potential applications in electrode materials in solar cells and electrochemical systems. Here we demonstrate the application of our conductive MWCNT/poly(TA) composite film as the top electrode in perovskite solar cells (C-PSCs) with promising performance. The developed C-PSCs exhibit a stable and high-power conversion efficiency of 14.2%, which is highly significant for a newly developed carbon electrode-based PSC.