Dr Christopher Smith


Research Fellow
Ph.D. (Surrey), BSc (Hons) in Chemistry

Biography

In the media

Scaling up of graphene to power the Internet of Things
Author / Researcher
www.surrey.ac.uk
Innovative materials on display during Science Week
Author / Researcher
www.gov.uk

Research

Research interests

My publications

Publications

Smith, C.T.G., Rhodes, R.W., Beliatis, M.J., Jayawardena, K.I., Rozanski, L.J., Mills, C.A. and Silva, S.R.P. (2014). Graphene oxide hole transport layers for large area, high efficiency organic solar cells - Applied Physics Letters, 105(7), p.073304.
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Graphene oxide (GO) is becoming increasingly popular for organic electronic applications. We present large active area (0.64 cm2), solutionprocessable, poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:[6,6]-Phenyl C71 butyric acid methyl ester (PCDTBT:PC70BM) organic photovoltaic (OPV) solar cells, incorporating GO hole transport layers (HTL). The power conversion efficiency (PCE) of ∼5% is the highest reported for OPV using this architecture. A comparative study of solution-processable devices has been undertaken to benchmark GO OPV performance with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) HTL devices, confirming the viability of GO devices, with comparable PCEs, suitable as high chemical and thermal stability replacements for PEDOT:PSS in OPV.
Rozanski, L.J., Smith, C.T.G., Gandhi, K.K., Beliatis, M.J., Dabera, G.D.M., Jayawardena, K.I., Adikaari, A.D.T., Kearney, M.J. and Silva, S.R.P. (2014). A critical look at organic photovoltaic fabrication methodology: Defining performance enhancement parameters relative to active area - Solar Energy Materials and Solar Cells, 130, pp.513-520.
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With the ever-increasing focus on obtaining higher  conversion efficiencies (PCEs) for organic  (OPV), there is a need to ensure samples are measured accurately. Reproducible results are required to compare data across different research institutions and countries and translate these improvements to real-world production. In order to report accurate results, and additionally find the best-practice methodology for obtaining and reporting these, we show that careful analysis of large data sets can identify the best fabrication methodology. We demonstrate which OPV outputs are most affected by different fabrication or , and identify that masking effects can result in artificially-boosted PCEs by increasing fill factor and , requiring care when selecting which mask to use. For example, our best performing devices (>6% efficiency) show that the smallest mask areas have not produced a surfeit of the highest performers, with only 11% of the top performing devices measured using a 0.032 cm2 mask area, while 44% used the largest mask (0.64 cm2). This trend holds true for efficiencies going down to 5%, showing that effective fabrication conditions are reproducible with increasing mask areas, and can be translated to even larger device areas. Finally, we emphasise the necessity for reporting the best PCE along with the average value in order to implement changes in real-world production.
Liang, H.F., Smith, C.T.G., Mills, C.A. and Silva, S.R.P. (2015). The band structure of graphene oxide examined using photoluminescence spectroscopy - Journal of Materials Chemistry C, 3(48), pp.12484-12491.
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Photoluminescence (PL) spectra have been used to elucidate the band structure of graphene oxide (GO) reduced in aqueous solution. The GO reduction is measured  the identification of four PL peaks produced from GO solutions with different concentrations. Using corresponding UV-visible and photoluminescence excitation (PLE) spectroscopy, and on progressing from high energy to low energy transitions, the four PL peaks are identified as σ–σ* and π–π* transitions, a π band tail due to oxygen localized states, and a π band tail due to trapped water, respectively. The labeling of the band structure has been used to challenge the prevailing assignation of the low energy transitions, reported in the literature, to molecular σ–σ* and π–π* transitions alone.
in situ via
Carreño, N.L.V., Escote, M.T., Valentini, A., McCafferty, L., Stolojan, V., Beliatis, M., Mills, C.A., Rhodes, R., Smith, C.T.G. and Silva, S.R.P. (2015). Adsorbent 2D and 3D carbon matrices with protected magnetic iron nanoparticles - Nanoscale, 7(41), pp.17441-17449.
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We report on the synthesis of two and three dimensional carbonaceous sponges produced directly from graphene oxide (GO) into which functionalized iron nanoparticles can be introduced to render it magnetic. This simple, low cost procedure, wherein an iron polymeric resin precursor is introduced into the carbon framework, results in carbon-based materials with specific surface areas of the order of 93 and 66 m2 g−1, compared to approx. 4 m2 g−1 for graphite, decorated with ferromagnetic iron nanoparticles giving coercivity fields postulated to be 216 and 98 Oe, values typical for ferrite magnets, for 3.2 and 13.5 wt% Fe respectively. The strongly magnetic iron nanoparticles are robustly anchored to the GO sheets by a layer of residual graphite, on the order of 5 nm, formed during the pyrolysis of the precursor material. The applicability of the carbon sponges is demonstrated in their ability to absorb, store and subsequently elute an organic dye, Rhodamine B, from water as required. It is possible to regenerate the carbon-iron hybrid material after adsorption by eluting the dye with a solvent to which it has a high affinity, such as ethanol. The use of a carbon framework opens the hybrid materials to further chemical functionalization, for enhanced chemical uptake of contaminants, or co-decoration with, for example, silver nanoparticles for bactericidal properties. Such analytical properties, combined with the material's magnetic character, offer solutions for environmental decontamination at land and sea, wastewater purification, solvent extraction, and for the concentration of dilute species.
Kurzyp, M., Mills, C.A., Rhodes, R., Pozegic, T.R., Smith, C.T.G., Beliatis, M.J., Rozanski, L.J., Werbowy, A. and Silva, S.R.P. (2015). Filtration properties of hierarchical carbon nanostructures deposited on carbon fibre fabrics -Journal of Physics D: Applied Physics, 48(11), p.115305.
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Hierarchical carbon nanostructures have been produced and examined for their use in liquid filtration experiments. The nanostructures are based on carbon nanotube growth and graphite oxide sponge deposition on the surface of commercially available carbon fibre fabrics. The hierarchical nanomaterial construction on the carbon fibre fabric is made possible due to the chemical vapour deposited carbon nanotubes which act as anchoring sites for the solution deposited sponge nanomaterial. The nanomaterials show a high capacity for Rhodamine B filtration, with the carbon fibre—carbon nanotube—graphite oxide sponge fabric showing filtering performance comparable to a commercial activated carbon filter. After 40 successive filtrations of 10 mg ml−1 Rhodamine B solution, the filtrate of dual modified fabrics returned an increase in transparency of 94% when measured at approx. 550 nm compared to 72% for the commercial carbon filter. When normalised with respect to the areal density of the commercial filter, the increase in optical transparency of the filtrate from the dual modified fabrics reduces to 65%. The Rhodamine B is found to deposit in the carbon nanomaterials via a nucleation, growth and saturation mechanism.
Jayawardena, K.I., Li, S., Sam, L.F., Smith, C.T.G., Beliatis, M.J., Gandhi, K.K., Prabhath, M.R., Pozegic, T.R., Chen, S., Xu, X. Dabera, G.D.M. Rozanski, L.J., Sporea R.A., Mills, C.A., Guo, X. and Silva, S.R.P. (2015). High efficiency air stable organic photovoltaics with an aqueous inorganic contact. Nanoscale, 7(34), pp.14241-14247.
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We report a ZnO interfacial layer based on an environmentally friendly aqueous precursor for organic photovoltaics. Inverted PCDTBT devices based on this precursor show power conversion efficiencies of 6.8–7%. Unencapsulated devices stored in air display prolonged lifetimes extending over 200 hours with less than 20% drop in efficiency compared to devices based on the standard architecture.
Nagavolu, C., Susmitha, K., Raghavender, M., Giribabu, L., Rao, K.B.S., Smith, C.T.G., Mills, C.A., Silva, S.R.P. and Srikanth, V.V.S.S. (2016). Pt-free spray coated reduced graphene oxide counter electrodes for dye sensitized solar cells. Solar Energy, 137, pp.143-147.
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Graphene oxide (GO) was synthesized using a modified Hummers method and was reduced by using focused sunlight to obtain solar reduced graphene oxide (SRGO). GO and SRGO are then used as Pt-free counter electrode materials in dye sensitized solar cells (DSSCs). GO and SRGO counter electrodes were prepared by a simple spray coating method to produce homogeneous electrode layers. The DSSCs with GO and SRGO counter electrodes exhibited an overall power conversion efficiencies of ∼3.4 and ∼4%, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the DSSC with SRGO counter electrode exhibits higher electro-catalytic activity and lower charge transfer resistance at the electrode/electrolyte interface (in comparison to the DSSC with GO) resulting in higher conversion efficiency. Moreover, the microstructural features of SRGO are found to be suitable for its improved interaction with the liquid  and the enhanced electro-catalytic activity at its surface.