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Facile and purification-free synthesis of nitrogenated amphiphilic graphitic carbon dots Byung Joon Moon, Yelin Oh, Dong Heon Shin, Sang Jin Kim, Sanghyun Lee, Tae-Wook Kim, Min Park, and Sukang Bae Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.5b04915 • Publication Date (Web): 22 Feb 2016 Downloaded from http://pubs.acs.org on February 23, 2016
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Chemistry of Materials
Facile and purification-free synthesis of nitrogenated amphiphilic graphitic carbon dots Byung Joon Moon,1† Yelin Oh,1† Dong Heon Shin,1 Sang Jin Kim,1 Sanghyun Lee,1,2 Tae-Wook Kim,1,2 Min Park1 and Sukang Bae1*
1
Soft Innovative Materials Research Center, Korea Institute of Science and Technology,
Eunha-ri san 101, Bongdong-eup, Wanju-gun, Jeollabukdo (or Jeonbuk) 565-905, Republic of Korea. 2
Department of Nano Material Engineering, Korea University of Science and Technology,
217 Gajeong-ro, Yuseong-gu, Daejeon 305-350, Republic of Korea
∗
Corresponding author. Tel.: +82-63-219-8158; Fax.: +82-63-219-8129 E-mail address:
[email protected] (S. Bae)
†
These authors contributed equally to this paper.
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Abstract
The emerging carbon-based quantum dots have been attracting attention because of their tremendous potential for optoelectronic and biomedical applications, which is due to their unique and size-tunable optical properties, their ability to be functionalized, and their biocompatibility. Here, we report the facile one-step synthesis of highly fluorescent and amphiphilic n-doped graphitic carbon dots (N-GCDs) using a fumaronitrile (FN) precursor. An interesting property of the prepared GCDs is their near pH neutral dispersibility without refinement, which stands in contrast to reported methods. This finding indicates that our approach could lead to low-cost and efficient processability that is scalable and environmentally friendly. In addition, we find that our N-GCDs have high density of graphitic structure such as sp2-hybridized carbon and tiny amounts of defect by near-edge X-ray absorption fine structure (NEXAFS) results. Finally, to confirm the electro-optical behavior of N-GCDs on photovoltaic devices, we fabricate iPSCs consisting of ITO/PEIE/PTB7:PC71BM (+ N-GCDs)/MoO3/Ag. Using this effective approach, we demonstrate the highest conversion efficiency of ~8.6% resulting from improved photo-responsibility and charge transport based on various charge and energy transfer dynamics. Also, we believe that the shape, size and functionality of these GCDs can be controlled using other chemical species to provide a variety opportunities for use in optoelectronics, biological applications and sensors.
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Chemistry of Materials
INTRODUCTION Quantum dots (QDs), which are semiconductor nanocrystals with dimensions smaller than the exciton Bohr radius, show unique size effects and outstanding electronic, optical and electrochemical properties.1 Among these features is fluorescence, which is one of the most important properties of QDs. Over the past two decades, properties including high quantum yields, good photo-stability and resistance to photobleaching have led to QDs being utilized for light-emitting diodes (LEDs), biomedical imaging and biosensing.2-5 However, most of the high-performance QDs are composed of heavy metal elements (i.e., Cd, Pb and Hg), which limits QD applications due to their toxicity and potential environmental hazards. Recently, carbon-based fluorescent nanomaterials, especially carbon dots (CDs), graphene quantum dots (GQDs) and graphitic carbon dots (GCDs), have attracted much attention for its promising applications in opto-electronics, metal ion detection and biological research due to their low toxicity, unique spin property, robust chemical inertness, excellent biocompatibility and low cost.6-14 During the last decade, various methods have been developed to fabricate carbon based QDs that can be roughly classified into “top-down” and “bottom-up” approaches. “Top-down” approaches, which are based on reducing the size of large carbon materials, commonly involve complicated reactions or time-consuming purification processes.1518
Unlike “top-down” approaches, “bottom-up” methods, in particular pyrolysis
methods, are efficient synthetic routes that avoid several problems (e.g., carbonaceous aggregation, poor size control and uniformity, and unwanted surface properties) with relative ease and can produce carbon based QDs on a large scale.19-21 However, most of them that have been prepared via pyrolysis are mainly composed of sp3-hybridized carbon (low sp2/sp3 ratio) and possess substantial amounts of amorphous carbon structures. This is because of multiple factors that include 1) QDs being fabricated from non-graphitic and amorphous carbon sources (e.g., citric acid, glucose, L3 ACS Paragon Plus Environment
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glutamic acid and urea),22-25 2) the dehydration process for converting C-C bonds (C atoms with sp3-hybridized orbitals) to C=C bonds (C atoms with sp2-hybridized orbitals) is not available via bottom-up approaches at short reaction times (~10 min) and low process temperatures
