Broadband Flexible Quantum Dots/Graphene Photodetectors

Abstract

Nanohybrids consisting of quantum dots and graphene (QD/graphene) provides a unique scheme to design quantum sensors. The quantum confinement in QDs enables spectral tunability, while that in graphene provides superior photocarrier mobility. The combination of them allows for broadband light absorption and high photoconduction gain that in turn leads to high photoresponsivity in QD/Gr nanohybrid photodetectors. Since the first QD/graphene photodetector was reported in 2012, intensive research has been conducted on this topic. In this paper, a review of the recent progress made on QD/Gr nanohybrid photodetectors will be provided. Among many applications, there will be a particular focus on broadband and flexible photodetectors, which make use of the inherent advantages of the QD/Gr nanohybrids. The remaining challenges and future perspectives will be discussed in this emerging topic area.

Keywords: broadband photodetection; flexible; graphene; high sensitivity; quantum dots.

Figure 1

Device structures of four common types of flexible photodetectors: (a) photoconductors, (b) photodiodes, (c) phototransistors and (d) photoconductive nanohybrids.

Figure 2

The detection mechanisms of QD-based (a) photodiodes, (b) Gr-only photoconductors, and (c) Gr/QD nanohybrids. Red/blue dots and arrows represent positively/negatively charged carriers and the direction of movement, respectively.

Figure 3

(a) An array of QD/graphene channel with varied channel geometry. (b,c) Responsivity vs. channel length and width, respectively. (d,e) Noise current density vs. channel length and width, respectively. The inset of (d) shows a typical noise spectral density of graphene. Adapted with permission from Ref. [42]. Copyright 2024 American Chemical Society.

Figure 4

Light absorption and carrier transfer in a QD/graphene nanohybrid with varied layer thicknesses: (a) Thin QD layer with lower light absorption. (b) Optimal QD layer thickness to allow for maximum incident light absorption and all photocarriers collected. (c) QD layer too thick, with a substantial fraction of photocarrier recombined before completing transfer to graphene.

Figure 5

(a) Detection spectrum of QD/Gr nanohybrids. (b) Emission spectral range of various QDs of varied size. (c) Flexibility granted by the thin nature of graphene and fluid-like deformability of QDs. Adapted with permission from Ref. [11]. Copyright 2019 American Chemical Society.

Figure 6

(a) Pixelated multi-QD photodetector for color detection [65]. (b) Tandem structured multi-QD photodetector for color detection [91]. (c) Imaging with QD/graphene photodetectors in the NIR to SWIR range [92]. (d) Imaging with QD/graphene photodetectors in the visible–SWIR–MIR range [90]. Adapted with permission from Ref. [65]. Copyright 2019 American Chemical Society. Adapted with permission from Ref. [91]. Copyright 2024 John Wiley & Sons. Adapted with permission from Ref. [92]. Copyright 2024 American Chemical Society. Copyright 2025 American Chemical Society.

Figure 7

Four examples of flexible photodetectors from recent works. (a) A graphene-only flexible imager. (b) A QD-only flexible imager. (c) A QD/graphene nanohybrid imager. (d) A QD/MXene nanohybrid imager. Adapted with permission from Ref. [116]. Copyright 2024 John Wiley & Sons. Adapted with permission from Ref. [117]. Copyright 2019 John Wiley & Sons. Adapted with permission from Ref. [86]. Copyright 2024 American Chemical Society. Adapted with permission from ref. [118]. Copyright 2023 American Chemical Society.

Figure 8

Four examples of curved photodetector arrays from recent works. (a) An array of MoS₂-Graphene curved phototransistors. (b) An array of MoS₂-pV3D3 curved phototransistors. (c) An array of organic semiconductor based curved phototransistors. (d) An inhomogeneous array of Si photodiodes for undistorted imaging. Adapted with permission under a Creative Commons CC License from Ref. [119]. Adapted with permission under a Creative Commons CC License from Ref. [120]. Adapted with permission from Ref. [121]. Copyright 2023 John Wiley and Sons. Adapted with permission under a Creative Commons CC License from Ref. [122].