Enhanced Charge Transfer and Responsivity in Hybrid Quantum Dot/Graphene Photodetectors Using ZnO as Intermediate Electron‐Collecting Layer

Abstract

Hybrid graphene (Gr)–quantum dot (QD) photodetectors have shown ultrahigh photoresponsivity combining the strong light absorption of QDs with the high mobility of Gr. QDs absorb light and generate photocarriers that are efficiently transported by Gr. Typically, hybrid PbS–QD/graphene photodetectors operate by transferring photogenerated holes from the QDs to Gr while photoelectrons stay in the QDs inducing a photogating mechanism that achieves a responsivity of 6 × 107 A W−1. However, despite such high gain, these systems have poor charge collection with quantum efficiency below 25%. Herein, a ZnO intermediate layer (PbS‐QD/ZnO/Gr) is introduced to improve charge collection by forming an effective p‐n PbS‐ZnO junction driving the electrons to the ZnO layer and then to Gr. This improves the photoresponsivity of the devices by nearly an order of magnitude with respect to devices without ZnO. Charge transfer to Gr is demonstrated by monitoring the change in Fermi level under illumination for conventional PbS‐QD/Gr and for ZnO intermediate PbS‐QD/ZnO/Gr devices. These results improve the capabilities of hybrid QD/Gr configurations for optoelectronic devices.

π–π Interactions Mediated Pyrene Based Ligand Enhanced Photoresponse in Hybrid Graphene/PbS Quantum Dots Photodetectors

“…At low intensities of ≈10 −12 Watts (λ = 635 nm), the responsivity is 3 × 10 7 A W −1 , which is in line with the magnitude found for such hybrid SLG/QD devices. [ 20,21,23,27,56 ] These results show that the use of PBA QDs as a priming layer enhances the responsivity performance of SLG/QD devices through a stronger interaction between the two nanomaterials, but also induces a slower response.…”

“…[ 9–13 ] Recently, hybrid photoconductive detectors, combining QDs as light absorbers and photocarrier generators with graphene or other 2D materials as charge collectors, have attracted great interest due to their ultrahigh gain and high responsivity (10 7 A W −1 ), enabling high‐sensitivity and gate‐tunable photodetection. [ 14–27 ] Recent advances in hybrid photodetectors combining 2D materials and PbS or other QDs are summarized in Table S1 in Supporting Information. In graphene/PbS QD based photodetectors, the band offset at the graphene/QD junction induces a built‐in potential that keeps the photogenerated electrons in the QDs and transfers photo‐holes to graphene producing a photogating effect, leading to a change of carrier density and a photocurrent under the bias voltage V SD across graphene, as shown in Figure a.…”

Fabrication of graphene: CdSe quantum dots/CdS nanorod heterojunction photodetector and role of graphene to enhance the photoresponsive characteristics

“…This behavior has also been observed in other systems such as Gr/PbS, perovskite nanostructures, etc. [19,43,44]. .…”

Recent Progress on Graphene Flexible Photodetectors

“…Combining graphene with QDs can also extend the lifetime of induced photon carriers, which helps to obtain devices that can achieve a high-response light detection distribution. Hybrid graphene–QDPDs combine the strong light absorption of QDs with the high mobility of graphene, in which the QDs absorb light and generate photogenerated carriers efficiently transported by graphene [ 139 , 140 , 141 ]. To enhance the efficiency and stability of graphene/Si QD (SQD)-embedded SiO 2 (SQD:SiO 2 ) ML heterojunction PDs, Shin et al [ 142 ] employed bis (TFSA) as a dopant for graphene.…”