A large area flexible p-type transparent conducting CuS ultrathin films generated at liquid-liquid interface

The preparation of highly transparent, electrically conducting materials (TCMs) in the form of thin films possesses many applications, including touch screens, solar cells, smart glass, etc. Designing and making high-performance p-type materials that can match to n-type counter parts are found to be challenging even today. These thin films can be prepared directly on the substrates or more conveniently transferred to the desired substrates after the synthesis. Synthesis of ultrathin films of metal sulfide by simple liquid-liquid interface method has been known previously. However, transferring these films onto a substrate of considerable dimensions has always been a constant challenge as these films tend to break during the lift-off process. Furthermore, the transparency of these films is generally low due to the high roughness of these films. Here, we report CuS ultrathin film synthesis with varying thicknesses (similar to 15 nm - 40 nm) by a modified liquid-liquid interface method. We have developed two strategies to transfer these ultrathin films produced at a liquid-liquid interface onto any substrate with considerable dimensions (up to 8 cm x 4 cm) without losing electrical continuity. Optical and electrical measurements reveal that CuS thin films show a p-type conductivity with 10(2) -10(3) S/cm and having transparency between 90-93% at 550 nm, which are among the highest for p-type materials known today. Further, these films on plastic substrates show highly flexible properties, which ITO lacks. We could also extend this technique to transfer large area ZnS thin-films from the liquid-liquid interface to the desired substrates. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study reports the synthesis of ultrathin CuS films with varying thicknesses using a modified liquid-liquid interface method, along with the development of strategies to transfer these films onto substrates of considerable dimensions without losing electrical continuity. The CuS thin films exhibit high conductivity and transparency, with excellent flexibility on plastic substrates, showing promise for various applications in the field of transparent, electrically conducting materials.