Solution-Processed Graphene–Nanographene van der Waals Heterostructures for Photodetectors with Efficient and Ultralong Charge Separation

Our group has been involved in an interesting study of the photoconductivity of solution-processed nanographene ad-layers. Sensitization of graphene with inorganic semiconducting nanostructures has been demonstrated as a powerful strategy to boost its optoelectronic performance. However, the limited tunability of optical properties and toxicity of metal cations in the inorganic sensitizers prohibits their widespread applications, and the in-depth understanding of the essential interfacial charge-transfer process within such hybrid systems remains elusive. Here, we design and develop high-quality nanographene (NG) dispersions with a large-scale production using high-shear mixing exfoliation. The physisorption of these NG molecules onto graphene gives rise to the formation of graphene−NG van der Waals heterostructures (VDWHs), characterized by strong interlayer coupling through π−π interactions. As a proof of concept, photodetectors fabricated on the basis of such VDWHs show ultrahigh responsivity up to 4.5 × 107 A/W and a specific detectivity reaching 4.6 × 1013 Jones, being competitive with the highest values obtained for graphene-based photodetectors. The outstanding device characteristics are attributed to the efficient transfer of photogenerated holes from NGs to graphene and the long-lived charge separation at graphene−NG interfaces (beyond 1 ns), as elucidated by ultrafast terahertz (THz) spectroscopy. These results demonstrate the great potential of such graphene−NG VDWHs as prototypical building blocks for high-performance, low-toxicity optoelectronics. The study is published in https://doi.org/10.1021/jacs.1c07615.