Transparent conductive films (TCFs) are an important component of touch screens, smart windows, liquid crystal displays, organic light-emitting diodes (OLEDs), and organic photovoltaic cells. Indium tin oxide (ITO) has been the most widely used transparent conductive material, while the limited reserves of indium and the brittle nature of ITO hinder its sustainable application in flexible electronics.

With excellent flexibility, desirable optical properties and good electrical conductivity, single-wall carbon nanotube (SWCNT) networks is a promising candidate for making flexible TCFs. However, the reported optoelectronic performance of SWCNT TCFs is far away from those of ITO TCFs due to the challenging issues like the intertube junction resistance and bundling effect.

In a recent study published in Science Advances, Prof. CHENG Huiming and Prof. LIU Chang’s group at Institute of Metal Research of Chinese Academy of Sciences and the collaborators synthesized a SWCNT thin films composed of isolated SWCNTs with carbon-welded joints for TCFs by an injection floating catalyst chemical vapor deposition method.

By tuning the nucleation and growth concentration of SWCNTs, 85% the SWCNTs were isolated. By controlling the content of carbon source, a “carbon welding” structure was formed at tube-tube junctions.

Scientists demonstrated that the carbon-welded joints convert Schottky contacts between metallic and semiconducting SWCNTs into near-ohmic ones, which significantly lowers the intertube junction resistance.

Due to their unique structure, the pristine SWCNT films showed a record low sheet resistance of 41Ω □^-1 at 90% transmittance for 550-nm light. After HNO₃ treatment, the sheet resistance further decreases to 25Ω □^-1, better than that of ITO on a flexible substrate.

Using this SWCNT film as anodes, the OLEDs constructed demonstrated a high current efficiency of 75 cd A^-1, 7.5 times higher than that of the best reported CNT anode–based OLEDs. The OLEDs also exhibited excellent flexibility and stability.

These high-performance SWCNT TCFs with good flexibility showed a great potential for use in various flexible electronic and photoelectronic devices as a transparent electrode.