A high-performance transparent photodetector via building hierarchical g-C3N4 nanosheets/CNTs van der Waals heterojunctions by a facile and scalable approach

Graphitic-carbon nitride (g-C3N4) as a novel two-dimensional (2D) material has attracted considerable attentions due to its unique properties and diverse applications. However, the poor electron-hole (e-h) separation efficiency and short carrier diffusion length greatly hinder its application in optoelectronic devices. Here, we present a solution-processed photodetector based on the g-C3N4 nanosheets and carbon nanotubes (CNTs). Through a layer by layer spin coating method, a grid-like active layer with a large number of g-C3N4 nanosheets/CNTs van der Waals heterojunctions can be assembled. This subtle structure endows the device an outstanding photoelectric conversion performance as well as a high transparency (72%). The photodetector exhibits a broadband response to UV and visible light. Under 365 nm UV illumination, a high responsivity up to 0.23 A/W has been obtained, which exceeds those of most current transparent photodetectors. This work not only presents the first transparent device based on g-C3N4, but also provides a paradigm on designing low-cost and high performance electronic devices with van der Waals heterojunctions.