Future Perspectives and Review on Organic Carbon Dots in Electronic Applications Maria Semeniuk,†,⊥ Zhihui Yi,†,⊥ Vida Poursorkhabi,† Jimi Tjong,† Shaffiq Jaffer,† Zheng-Hong Lu,‡ and Mohini Sain*,†,§,∥
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Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Ontario M5S 3B3, Canada ‡ Department of Material Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3A1, Canada § Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, Ontario M5S 3G8, Canada ∥ Department of Mechanical Engineering, Beijing University of Chemical Technology (BUCT), 100029 Beijing, P.R. China ABSTRACT: Over the span of the past decade, carbon dots (CDs) synthesized from renewable organic resources (organic CDs) have gathered a considerable amount of attention for their photoluminescent properties. This review will focus on organic CDs synthesized using clean chemistry and conventional synthetic chemistry from organic sources and their fluorescence mechanisms, such as quantum confinement effect and surface/edge defects, before outlining their performance in electronic applications, including organic photovoltaic devices, organic light-emitting devices, biosensors, supercapacitors, and batteries. The various organic resources and methods of organic CDs synthesis are briefly covered. Many challenges remain before the adoption of CDs can become widespread; their characterization, structure, functionality, and exact photoluminescent mechanism all require additional research. This review aims to summarize the current research outcomes and highlight the area where further research is needed to fully use these materials. KEYWORDS: carbon dots, fluorescent, photoluminescent, photoluminescent mechanism, organic photovoltaic devices, organic light-emitting devices, biosensors, supercapacitors, batteries natural organic CDs application,16,17 and a few have mentioned food and safety applications.18 Small incremental advancements in photoluminescent QY intensity have been seen when altering CDs synthesis methods, and these CDs have been used in various bioimaging techniques and electronic devices. With these CDs, research has been carried out on the development of CD-based organic electronics. Results show that CDs act as an excellent interface and promote the interactions between electrode and electrolyte in supercapacitors, resulting in an increase in their specific capacitance, rate performance, and cycling stability. In organic light-emitting devices (OLEDs), the CDs have been developed as environmentally friendly with a stable, tunable emission with a large photoluminescence (PL) bandwidth.19,20 CDs in biosensors are biocompatible and have been fabricated with signal on or off processes. CDs in organic photovoltaic devices (OPVs) and OLEDs alter the device’s
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arbon dots (CDs) are nanosized carbon particles, which have attracted a lot of great attention since 2006 as an environmentally friendly replacement for toxic quantum dots (QDs).1 CDs were first prepared in 2004 as carbon templates on Si(100).2 The primary advantages of CDs include nontoxicity, high quantum yield (QY) with a tunable band gap, photostability, low cost, and high surface passivation. Other advantageous properties of CDs include excellent biocompatibility, chemical inertness, and high specific surface area.3−5 Organic CDs, produced from organic precursors, including naturally occurring substances, show promising characteristics especially suitable for photoelectric applications. Significant advances have been made in CDs research recently, the most noteworthy being a group which produced CDs made from citric acid and diamine ethylene with a QY of 80%.6 Many recent reviews have been written on synthesis, characterizations, and applications in both electronic and biological applications, which summarize the field of CDs well.3,7−15 Furthermore, limited reviews have been written on the synthesis of natural CDs, however, none mention their © 2019 American Chemical Society
Received: January 25, 2019 Accepted: May 30, 2019 Published: May 30, 2019 6224
DOI: 10.1021/acsnano.9b00688 ACS Nano 2019, 13, 6224−6255
Review
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Cite This: ACS Nano 2019, 13, 6224−6255
Review
ACS Nano
Figure 1. Three types of CDs and their structures graphene quantum dots (GQDs), carbon nanodots (CNDs), and polymer dots (PDs). Reprinted with permission from ref 32. Copyright 2015 Springer Nature.
work function of organic CDs in organic electronics. As well, we have summarized the potential applications for organic CDs in organic (bio)electronics including OLEDs, energy storage devices, biosensors, and OPVs. We have also discussed device performance and its limitations. Finally, we put forward our perspective to address some of the challenges associated with organic CDs and their possible remedies.
photoelectrical properties, including efficiency and functionality.21 Nevertheless, few papers have discussed the synthesis mechanism of organic CDs16,17 and the photoluminescent mechanism of organic CDs in electronic devices, which are important for rational design, synthesis, and fabrication processes. Over the last 15 years, CDs have been synthesized in various ways. However, there are many drawbacks of conventional technologies for preparing the CDs, such as complicated steps, hard-to-find equipment, high temperatures, toxic reagents, and high cost, largely limiting their practical applications. Recent research has been undertaken to investigate alternative resources for the production of organic CDs. These approaches look for sustainable materials which are low cost, scalable, industrially and economically attractive, and based on renewable and highly abundant resources.22 By making use of various resources, organic CDs with various colors, superior properties have been developed, such as the lack of photoblinking due to πconjugation after surface passivation.1 The photostability of organic CDs plays an important role for organic CDs to be employed in light-emitting devices (LEDs). However, selfabsorbance occurs owing to the wide band gap of the CDs, which leads to low QY of CDs in a solid state. All in all, the structure of organic CDs decides the intrinsic properties of CDs, which the desired configurations of CDs are still uncontrollable owing to the lack of theoretical supervision and the self-assembly process under the hydrothermal synthesis conditions. Meanwhile, recently developed CD-based electronic biosensors have been widely ignored in respects of the dopants, the mechanisms, and the device design and fabrication. So far, there has been not a comprehensive review of organic CDs derived from diverse sources of organic matters with an enhanced understanding of mechanism the of fluorescence in organic electronics. This review discusses the differences between types of organic CDs and their various photoluminescent mechanisms. More specifically, this review briefly addresses the synthesis process and a detailed description of the characterizations of CDs, allowing us to better understand the luminescent behavior and
TYPES OF CARBON DOTS “Carbon dots” is a term used for various nanosized carbon materials with fluorescence; the size of the nanoparticles is usually
