Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Graphene: The New Two-Dimensional Nanomaterial

Approaches, Derivatives and Applications Vasilios Georgakilas,† Michal Otyepka,‡ Athanasios B. Bourlinos,‡ Vimlesh Chandra, Namdong Kim, K. Christian Kemp, Pavel Hobza,‡,§,⊥ Radek Zboril,*,‡ and Kwang S. Kim* †Institute of Materials Science, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo naḿ. 2, 166 10 Prague 6, Czech Republic

Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications

Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

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Graphene-based composites

Graphene based materials: Past, present and future

Herein we obtained a chemically bonded TiO2 (P25)-graphene nanocomposite photocatalyst with graphene oxide and P25, using a facile one-step hydrothermal method. During the hydrothermal reaction, both of the reduction of graphene oxide and loading of P25 were achieved. The as-prepared P25-graphene photocatalyst possessed great adsorptivity of dyes, extended light absorption range, and efficient charge separation properties simultaneously, which was rarely reported in other TiO2−carbon photocatalysts. Hence, in the photodegradation of methylene blue, a significant enhancement in the reaction rate was observed with P25-graphene, compared to the bare P25 and P25-CNTs with the same carbon content. Overall, this work could provide new insights into the fabrication of a TiO2−carbon composite as high performance photocatalysts and facilitate their application in the environmental protection issues.

P25-Graphene Composite as a High Performance Photocatalyst

A soluble graphene, which has a one-atom thickness and a two-dimensional structure, is blended with poly(3-hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction (BHJ) polymer photovoltaic cells. Adding graphene to the P3HT induces a great quenching of the photoluminescence of the P3HT, indicating a strong electron/energy transfer from the P3HT to the graphene. In the photovoltaic devices with an ITO/PEDOT:PSS/P3HT:graphene/LiF/Al structure, the device efficiency increases first and then decreases with the increase in the graphene content. The device containing only 10 wt % of graphene shows the best performance with a power conversion efficiency of 1.1%, an open-circuit voltage of 0.72 V, a short-circuit current density of 4.0 mA cm−2, and a fill factor of 0.38 under simulated AM1.5G conditions at 100 mW cm−2 after an annealing treatment at 160 °C for 10 min. The annealing treatment at the appropriate temperature (160 °C, for example) greatly improves the device performance; however, an annealing at overgenerous conditions such as at 210 °C results in a decrease in the device efficiency (0.57%). The morphology investigation shows that better performance can be obtained with a moderate content of graphene, which keeps good dispersion and interconnection. The functionalized graphene, which is cheap, easily prepared, stable, and inert against the ambient conditions, is expected to be a competitive candidate for the acceptor material in organic photovoltaic applications.

Polymer Photovoltaic Cells Based on Solution-Processable Graphene and P3HT

In this paper, an organic photovoltaic device based on an acceptor of solution-processable functionalized graphene was designed. A short circuit current density (Jsc) of 4.0mAcm−2, open circuit voltage (Voc) of 0.72V, and a solar power conversion efficiency of 1.1% were obtained for the device of indium tin oxide/poly(ethylene dioxythiophene) doped with polystyrene sulfonic acid (40nm)/poly(3-hexylthiophene-1, 3-diyl):graphene (graphene 10wt%, 100nm)/LiF (1nm)/Al (70nm) after an annealing treatment under simulated AM1.5G 100mW illumination in air. Because of the low price, ease of preparation, and inertness against ambient conditions, soluble graphene will be a promising candidate used for acceptor materials in the photovoltaic applications.

Organic photovoltaic cells based on an acceptor of soluble graphene

Organic bulk heterojunction (BHJ) solar cells based on a dicyanovinyl-substituted oligothiophene as a donor and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as an acceptor were fabricated and characterized. The oligothiophene derivative can absorb long wavelength photons of the solar radiation, which makes the solar cells with an optimized weight ratio of 1:1.4 have a decent short-circuit current density (12.4 mA/cm2) and open-circuit voltage (0.88 V) under AM 1.5G illumination with an intensity of 100 mW/cm2. A power conversion efficiency (PCE) of 3.7% is achieved, which is among the best PCEs of solution processed small molecule BHJ solar cells.

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Solution-processed bulk heterojunction organic solar cells based on an oligothiophene derivative

Effect of cathode buffer layer on the stability of polymer bulk heterojunction solar cells

High-efficiency polymer solar cells were made with a hydrophilic graphene oxide (GO) doped in poly(ethylene dioxythiophene) (PEDOT)-polystyrene sulfonic acid (PSS) composites using a structure of indium tin oxide/PEDOT:PSS:GO (40 nm)/poly(3-hexylthiophene-1,3-diyl) (P3HT)-[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (1:0.6, 100 nm)/LiF (1 nm)/Al (70 nm). The energy conversion efficiency eta was enhanced from 2.1 to 3.8% by doping GO into the PEDOT:PSS buffer layer under AM1.5G 100 mW cm(-2) illumination in air. The pre-annealing of GO makes energy conversion efficiency 1.8 times that of the device based on a pristine PEDOT:PSS buffer layer. Because of the low price and ease of preparation, soluble graphene will be a promising buffer layer used in photovoltaic applications. Furthermore, it can be used in other electronic applications.

Liying Yang

Papers

Polymer Photovoltaic Cells Based on Solution-Processable Graphene and P3HT

Organic photovoltaic cells based on an acceptor of soluble graphene

Solution-processed bulk heterojunction organic solar cells based on an oligothiophene derivative

Effect of cathode buffer layer on the stability of polymer bulk heterojunction solar cells

Buffer layer of PEDOT:PSS/graphene composite for polymer solar cells.