Degree of functionalisation dependence of individual Raman intensities in covalent graphene derivatives

Vecera, Philipp; Eigler, Siegfried; Koleśnik-Gray, Maria; Krstić, Vojislav; Vierck, Asmus; Maultzsch, Janina; Schäfer, Ricarda A.; Hauke, Frank; Hirsch, Andreas

doi:10.1038/srep45165

Cited by 53 publications

(64 citation statements)

References 37 publications

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“…Correspondingly, the associated F-peak does not show sizeable variation either. [29,34] This is also consistent with the observed p-type behavior of the individual FGs. [33] The defect-related peaks at 1250, 1335, and 1610 cm −1 showed a weak red shift in their frequencies, however, their individual intensities remained largely constant ( Figure S4, Supporting Information).…”

Section: Fluorographenesupporting

confidence: 87%

Electrical Transport in Devices Based on Edge‐Fluorinated Graphene

Koleśnik-Gray

Sysoev

Gollwitzer

et al. 2018

Adv Elect Materials

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When considering fluorinated graphene (FG)-based functional device technology, the device architectures must be chosen adequately. Typically, functionalized graphene devices can be envisaged as either large scale (area)-based thin film structures or as systems integrated from individual nanoobjects. This implies potentially significant qualitative and quantitative differences in the device response. Specifically, the presence of edges in graphene can be decisive. Considering the electrical conductivity of individual mono-and fewlayer flakes, it is dominated by the type, amount, and bonding position (basal or edge) of functional groups attached to the C(sp 2 ) matrix. In thin film-based systems, however, the charge transport also is largely affected by the properties of edge/edge, edge/plane, and plane/plane junctions. [22] Therefore, electrical characterization is a primary means to evaluate and benchmark whether or not a given derivative meets the requirements for selected applications.In the present work we study the impact of F content and bonding position on the electronic properties of graphene fluorinated by BrF 3 vapor at room temperature [8,20] in the range of 2.4-16.6 at%. We compared the electrical conductivity of thin films with the conductivity of corresponding individual FG flakes which constitute the former. We found a significant difference in the conductivity dependence on the degree of fluorination for the two device architectures: While in the case of thin films, a strong decrease in conductivity with fluorine content was observed, individual flakes showed an increase in conductivity and exhibited graphene-like bipolar transfer characteristics with electron and hole mobilities of the order of few 1000s cm 2 V −1 s −1 for F content approaching 17 at%. With further aid of scanning electron and Raman microscopy, this qualitative difference between films and single flakes was attributed to the circumstance that the preferred sites for fluorination are at the edges rather than basal planes of the FG.For the characterization of thin film devices, 3 mm long and 1 mm wide structures were defined using a hard-mask technique (Figure 1a). FG dispersions were sprayed onto Si wafers with 300 nm thermal SiO 2 on top, resulting in homogeneous and continuous films (Figure 1b), which were then electrically contacted with conducting silver paste. For electrical characterization of individual flakes, small amounts of the dispersionsThe conductivity of few-and monolayer graphene with covalently bound moieties is a key-point in the potential application of these materials in any electrical and optoelectronic device. In particular, fluorination of such graphene-based systems is of interest, as fluorine is expected to have a strong influence on the charge-carrier density due to its high electronegativity, and therefore modify the electrical transport properties significantly. Here it is shown that, depending on the device architecture, the electrical properties of fluorinated graphene-based devices are significantly d...

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Section: Fluorographenesupporting

confidence: 87%

Electrical Transport in Devices Based on Edge‐Fluorinated Graphene

Koleśnik-Gray

Sysoev

Gollwitzer

et al. 2018

Adv Elect Materials

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“…As G‐β‐NiTPP‐N 2 + only can attack the peripheral edges of the intermediately exfoliated graphene flakes, no D‐band contribution of covalently attached porphyrin units in the carbon allotrope plane is expected. Nevertheless, as we have previously shown, graphenides represent highly reactive intermediates, which can undergo side reactions with any species present during their formation or in the course of the aqueous work up and therefore attribute to the detected D‐band . On this basis, the detected I D /I G intensity increase can be attributed to the attachment of proton‐ or hydroxyl functionalities.…”

Section: Methodsmentioning

confidence: 58%

Reductive Functionalization of Graphenides With Nickel(II) Porphyrin Diazonium Compounds

Hou

Dasler

Hauke

et al. 2017

Physica Rapid Research Ltrs

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A novel type of a graphene‐porphyrin hybrid with a direct covalent linker between graphene and a nickel(II) tetraphenylporphyrin unit has successfully been synthesized by the reductive exfoliation/functionalization of potassium intercalated graphite as starting material. Moreover, we directly compared the reactivity of two structurally different porphyrin derivatives, namely, meso‐NiTPP‐N2+, with the diazonium group in 4′‐position of a peripheral phenyl ring and a novel β‐NiTPP‐N2+ diazonium cation, where the diazonium group is directly attached to the β‐pyrrolic position of the 18 π electron core. Due to sterical restraints, this intermediately generated porphyrin radical cannot attack the extended π surface of graphene and only a functionalization of present dangling bonds at the flake edges may be obtained in this case. All reaction products have been analyzed in detail be means of Raman and UV/Vis spectroscopy as well as thermogravimetric analysis.

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“…The chemical structure was thoroughly investigated in an earlier study. [23][24][25]28] The microstructure of the ultrathin nanosheets of oxo-G/DA-wrapped perovskite formed during the crystallization of perovskite can effectively reduce the defects of oxo-G/DA agglomeration formation. In several reports, we have verified the size and layer distribution of oxo-G/DA nanosheets by particle size analyzer and atomic force microscopy (AFM).…”

Section: The Operational Mechanism Of Oxo-g/damentioning

confidence: 99%

Ultrathin Nanosheets of Oxo‐functionalized Graphene Inhibit the Ion Migration in Perovskite Solar Cells

Zuo

Qiong

et al. 2019

Advanced Energy Materials

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Recent progress of PSCs in efficiency and stability enhancement is addressed to the change of perovskite composition and crystal optimization. By introducing mixed cations and halide to adjust the composition of the organicinorganic hybrid perovskite, the crystal structure of the perovskite can be effectively improved, which ultimately led to the increased stability and efficiency of the PSCs. Compared with the single cation/ halide perovskite (methylammonium halide, formamidinium lead halide, and cesium lead halide), the mixed perovskite not only has higher PCE but also has better heat and humid air stability. [9][10][11][12] For mixed cation/halide perovskites, despite good optoelectronic properties, the mixing of multiple cations and halogens is prone to localized ionic enrichment during preparation, annealing, and operation. At the same time, as the cation and halide ions move in the builtin electric field of the device, local positive and negative ion vacancies are formed. These defects will cause significant hysteresis in the device and ultimately affect the performance of the device. [13][14][15][16][17] A series of studies on both experimental and theoretical methods [13,18,19] have been reported. Constraining Mixed cation/halide perovskites have led to a significant increase in the efficiency and stability of perovskite solar cells. However, mobile ionic defects inevitably exacerbate the photoinduced phase segregation and selfdecomposition of the crystal structure. Herein, ultrathin 2D nanosheets of oxo-functionalized graphene/dodecylamine (oxo-G/DA) are used to solve ion migration in cesium (Cs)-formamidinium (FA)-methylammonium (MA) triple-cation-based perovskites. Based on the superconducting carbon skeleton and functional groups that provide lone pairs of electrons on it, the ultrathin 2D network structure can fit tightly on the crystals and wrap them, isolating them, and thus reducing the migration of ions within the built-in electric field of the perovskite film. As evidence of the formation of sharp crystals with different orientation within the perovskite film, moiré fringes are observed in transmission electron microscopy. Thus, a champion device with a power conversion efficiency (PCE) of 21.1% (the efficiency distribution is 18.8 ± 1.7%) and a remarkable fill factor of 81%, with reduced hysteresis and improved long-term stability, is reported. This work provides a simple method for the improvement of the structural stability of perovskite in solar cells.

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Degree of functionalisation dependence of individual Raman intensities in covalent graphene derivatives

Cited by 53 publications

References 37 publications

Electrical Transport in Devices Based on Edge‐Fluorinated Graphene

Electrical Transport in Devices Based on Edge‐Fluorinated Graphene

Reductive Functionalization of Graphenides With Nickel(II) Porphyrin Diazonium Compounds

Ultrathin Nanosheets of Oxo‐functionalized Graphene Inhibit the Ion Migration in Perovskite Solar Cells

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