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1. Quantum Dot/Graphene Heterostructure Nanohybrid Photodetectors

   https://doi.org/10.1007/978-3-030-74270-6_5  

   Wu, Judy ; Gong, Maogang ; Schmitz, Russell C. ; Liu, Bo ( July 2021 , Lecture notes in nanoscale science and technology)

   Tong, Xin ; Wu, Jiang ; Wang, Zhiming (Ed.)

   Colloidal semiconductor quantum dot/graphene van der Waals heterostructure nanohybrids are emerging technologies for photodetection. These nanohybrids combine the advantages of the enhanced light-matter interaction and spectral tunability of quantum dots (QDs) and superior charge mobility in graphene, providing an affordable alternative for uncooled photodetectors with high gain or external quantum efficiency in a wide spectral range. In particular, the interfacing of QDs with high-mobility graphene as a charge transport pathway has provided an effective resolution to the critical issue of charge transport in QD-only photodetectors stemming from the low charge mobility associated with both QD surface defect states and QD-QD junctions. Furthermore, the achieved capability in industrial-scale fabrication of graphene, colloidal QDs, and QD/graphene nanohybrids has motivated efforts in researches of focal plane arrays that are expected to be not only high performance and low cost but also lightweight, flexible, and wearable. This chapter aims to provide an up-to-date review of the recent progress made in the research of QD/graphene nanohybrid photodetectors, together with a discussion on the challenges remaining and perspective in future research and development to make QD/graphene nanohybrids competitive for commercialization. 

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2. Explore uncooled quantum dots/graphene nanohybrid infrared detectors based on quantum dots/graphene heterostructures

   https://doi.org/10.1117/12.2556930  

   Wu, Judy Z. ( April 2020 , Infrared Technology and Applications XLVI, Vol 11407 (2020) SPIE Defense + Commercial Sensing (2020))

   Heterojunction nanohybrids based on low-dimension semiconductors, including colloidal quantum dots (QDs) and 2D atomic materials (graphene, transition metal chalcogenides, etc) provide a fascinating platform to design of new photonic and optoelectronic devices that take advantages of the enhanced light-solid interaction attributed to their strong quantum confinement and superior charge mobility for uncooled photodetectors with a high gain up to 1010. In these heterojunction nanohybrids, the van der Waals (vdW) interface plays a critical role in controlling the optoelectronic process including exciton dissociation by the interface built-in field that drives the follow-up charge injection and transport to graphene. In this paper, we present our recent progress in development of such heterostructures nanohybrids for uncooled infrared detectors including PbS and FeS2 QDs/graphene and 2D vdW heterostructures MoTe2/Graphene/SnS2 and GaTe/InSe. We have found that nonstoichiometric Fe1–xS2 QDs (x = 0.01–0.107) with strong localized surface plasmonic resonance (LSPR) can have much enhanced absorption in broadband from ultraviolet to short-wave infrared (SWIR, 1–3 μm). Consequently, the LSPR Fe1–xS2 QDs/graphene heterostructure photodetectors exhibit extraordinary photoresponsivity in exceeding 4.32 ×106 A/W and figure-of-merit detectivity D* < 7.50 ×1012 Jones in the broadband of UV–Vis–SWIR at room temperature. The 2D vdW heterostructures allows novel designs of interface band alignments with uncooled NIR-SWIR D* up to 1012 Jones. These results illustrate that the heterostructure nanohybrids provide a promising pathway for low-cost, printable and flexible infrared detectors and imaging systems. 

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3. Development of high-speed quantum dots/graphene infrared detectors for uncooled infrared imaging

   https://doi.org/10.1117/12.2589813  

   Wu, Judy Z. ; Gong, Maogang ; Schmitz, Russell C. ; Liu, Bo ( April 2021 , Infrared Technology and Applications XLVII, Vol 117410F (2021) SPIE Defense + Commercial Sensing (2021))

   Fulop, Gabor F. ; Kimata, Masafumi ; Zheng, Lucy ; Andresen, Bjørn F. ; Miller, John Lester (Ed.)

   Colloidal semiconductor quantum dots/graphene van der Waals (vdW) heterojunctions take advantages of the enhanced light-matter interaction and spectral tenability of quantum dots (QDs) and superior charge mobility in graphene, providing a promising alternative for uncooled infrared photodetectors with a gain or external quantum efficiency up to 1010. In these QD/graphene vdW heterostructures, the QD/graphene interface plays a critical role in controlling the optoelectronic process including exciton dissociation, charge injection and transport. Specifically, charge traps at the vdW interface can increase the noise, reduce the responsivity and response speed. This paper highlight our recent progress in engineering the vdW heterojunction interface towards more efficient charge transfer for higher photoresponsivity, D* and response speed. These results illustrate that the importance in vdW heterojunction interface engineering in QD/graphene photodetectors which may provide a promising pathway for low-cost, printable and flexible infrared detectors and imaging systems. 

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4. Near full light absorption and full charge collection in 1-micron thick quantum dot photodetector using intercalated graphene monolayer electrodes

   https://doi.org/10.1039/c9nr09901h  

   Chen, Wenjun ; Ahn, Seungbae ; Balingit, Marquez ; Wang, Jiaying ; Lockett, Malcolm ; Vazquez-Mena, Oscar ( February 2020 , Nanoscale)

   Quantum dots (QDs) offer several advantages in optoelectronics such as easy solution processing, strong light absorption and size tunable direct bandgap. However, their major limitation is their poor film mobility and short diffusion length (<250 nm). This has restricted the thickness of QD film to ∼200–300 nm due to the restriction that the diffusion length imposes on film thickness in order to keep efficient charge collection. Such thin films result in a significant decrease in quantum efficiency for λ > 700 nm in QDs photodetector and photovoltaic devices, causing a reduced photoresponsivity and a poor absorption towards the near-infrared part of the sunlight spectrum. Herein, we demonstrate 1 μm thick QDs photodetectors with intercalated graphene charge collectors that avoid the significant drop of quantum efficiency towards λ > 700 nm observed in most QD optoelectronic devices. The 1 μm thick intercalated QD films ensure strong light absorption while keeping efficient charge extraction with a quantum efficiency of 90%–70% from λ = 600 nm to 950 nm using intercalated graphene layers as charge collectors with interspacing distance of 100 nm. We demonstrate that the effect of graphene on light absorption is minimal. We achieve a time-modulation response of <1 s. We demonstrate that this technology can be implemented on flexible PET substrates, showing 70% of the original performance after 1000 times bending test. This system provides a novel approach towards high-performance photodetection and high conversion photovoltaic efficiency with quantum dots and on flexible substrates. 

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

   https://doi.org/10.1002/aelm.202100672  

   Ahn, Seungbae ; Ingrosso, Chiara ; Panniello, Annamaria ; Striccoli, Marinella ; Bianco, Giuseppe Valerio ; Agostiano, Angela ; Bruno, Giovanni ; Curri, Maria Lucia ; Vazquez‐Mena, Oscar ( October 2021 , Advanced Electronic Materials)

   Hybrid graphene and quantum dots (QDs) photodetectors merge the excellent conductivity and ambipolar electric field sensitivity of graphene, with the unique properties of QDs. The photoresponsivity of these devices depends strongly on the charge transfer at the graphene/QDs interface. Here 1‐pyrene butyric acid (PBA)‐coated PbS QDs with single layer graphene (SLG) are used to investigate the effect of pyrene as a π–π mediator to enhance charge transfer at the SLG/QDs junction under illumination. The surface chemistry at the QD–QD and SLG/QD interface is studied with the conventional tetrabutylammonium iodide (TBAI) QD linker. The hybrid SLG/QD photodetectors with PBA as a SLG‐QD linker demonstrate a photoresponse up to 30% higher than that recorded for devices where only TBAI is used, due to the strong electron coupling between SLG and QDs. Transconductance measurements show that PBA provokes electron depletion in SLG ascribed to the tendency to delocalize the QDs holes, favoring their transfer to SLG. This surface ligand is found to improve the interaction between the QDs light absorbers and the SLG charge collector, leading to an increased photodetection response. This demonstrates that ligand engineering can enhance charge dynamics and boost the performance of the hybrid device.

    

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