Praveen K. Surolia

Low toxicity functionalised imidazolium salts for task specific ionic liquid electrolytes in dye-sensitised solar cells: a step towards less hazardous energy production

Novel solvent free task specific ionic liquid (TSIL) electrolytes for dye sensitised solar cells (DSSC) were synthesised and tested. Of great concern is the replacement of low-moderate toxicity second generation ILs, with high toxicity third generation TSILs. As most 1-butyl-3-methylimidazolium (Bmim) and especially 1-ethyl-3-methylimidazolium (Emim) based ILs have low toxicity, the designing of replacement TSILs of comparable toxicity is a challenge. Structural features of TSIL investigated herein were incorporation of heteroatoms into the side chain of imidazolium cations (i.e. ether, ester and amide) and anion (bromide, iodide, and triflimide [NTf2]). Preliminary toxicity screening against 20 microorganisms (8 bacteria and 12 fungi) found that all ILs, imidazolium salts, N-butylbenzimidazole (NBB) and guanidinium thiocyanate (GNCS) do not exhibit high antimicrobial toxicity. However NBB and a pentyl ester substituted IL displayed moderate toxicity to several strains of bacteria and fungi. Further toxicity testing to establish IC50 values shows several novel TSIL compounds and imidazolium salts are in fact less toxic to microorganisms (e.g. bacteria) than commonly used 1-ethyl-3-methylimidazolium iodide (EmimI) and 1,3-dimethylimidazolium iodide (DmimI). We have demonstrated that the presence of ether and either ester or amide groups in the structure of the cation of the TSIL and imidazolium salts reduces antimicrobial toxicity, which is consistent with the lowering of the lipophilicity of ILs. Iodide and bromide analogues have lower toxicity than the NTf2 examples in this study. The DSSC performance using these “greener” ILs in place of the standard EmimI compare quite favourably. Two low antibacterial toxicity iodide examples exhibit photocurrents of 9.27 mA cm−2 and 8.85 mA cm−2, respectively, achieving promising efficiencies of 3.39% and 3.31%, respectively (EmimI = 4.94%). DSSC performance is further improved by 15% minimum to 66% maximum, depending on IL chosen, by the presence of small amounts of moisture and DSSCs employing a low antibacterial toxicity iodide TSIL or imidazolium salt can surpass the performance of dry EmimI. Of note the DSSC containing TSIL NTf2 examples, performed poorly compared to the halide analogues, with the outcome that the most toxic TSILs under investigation are also the least preferred based on performance.

BaTiO3 photoelectrodes for CdS quantum dot sensitized solar cells

For the first time, layers of nano-sized perovskite BaTiO3 particles were successfully applied as photoelectrodes for making CdS quantum dot sensitized solar cells (QDSSC). The optical and electrochemical properties of BaTiO3 on FTO glass substrates were studied. The performance of cells was maximized by controlling growth cycles of CdS and surface passivation of BaTiO3 films. The encouraging power conversion efficiency (PCE) of 1.51% achieved points to the potential of using perovskites for sensitization and co-sensitization applications in third generation solar cells. It agrees well with the recent trend of finding more compatible and stable perovskites for applications in mesoscopic sensitized solar cells.

Organic Dyes Containing Coplanar Dihexyl-Substituted Dithienosilole Groups for Efficient Dye-Sensitised Solar Cells

A chromophore containing a coplanar dihexyl-substituted dithienosilole (CL1) synthesised for use in dye-sensitised solar cells displayed an energy conversion efficiency of 6.90% under AM 1.5 sunlight irradiation. The new sensitiser showed a similar fill factor and open-circuit voltage when compared with N719. Impedance measurements showed that, in the dark, the charge-transfer resistance of a cell using CL1 in the intermediate-frequency region was higher compared to N719 (69.8 versus 41.3 Ω). Under illumination at AM 1.5G-simulated conditions, the charge-transfer resistances were comparable, indicative of similar recombination rates by the oxidised form of the redox couple. The dye showed instability in ethanol solution, but excellent stability when attached to TiO2. Classical molecular dynamics indicated that interactions between ethanol and the dye are likely to reduce the stability of CL1 in solution form. Time-dependent density functional theory studies were performed to ascertain the absorption spectrum of the dye and assess the contribution of various transitions to optical excitation, which showed good agreement with experimental results.

Electrophoretic separation and deposition of metal–graphene nanocomposites and their application as electrodes in solar cells

Graphene oxide (GO) is a 2D material which offers great promise in many applications, owing primarily to the reactive surface which enables an easy surface functionalization and solution processing of the resulting materials. Herein we demonstrate that graphene oxide (GO) can be used as a supporting template for the production of new graphene–metal nanoparticle composites. Our synthetic strategy allowed for nanoparticle deposition (Pt and Au) onto the surface of the 2 dimensional carbon nano-substrate without stabilising ligands. Moreover we have shown that the composite materials can be further processed using electrophoretic deposition (EPD). The deposition of the materials onto conducting glass substrates (namely fluorine doped tin oxide) via EPD, allows for the formation of high quality, stable electrodes. These electrodes demonstrated a tuneable electrochemical response towards the reduction of the tri-iodide ion, when studied electrochemically. These electrodes were then tested as potential counter electrodes (CEs) in dye sensitized solar cells (DSSCs) and displayed very promising results, increasing the efficiency by 47.5%, when compared to a conventional Pt electrode.

Renewable energy technologies and its adaptation in an urban environment

This general article is based on the inaugural talk delivered at the opening of OMTAT 2013 conference. It notes that the integration of renewable energy sources into living and transport sectors presents a daunting task, still. In spite of the fact that the earth and its atmosphere continually receive 1.7 × 1017 watts of radiation from the sun, in the portfolio of sustainable and environment friendly energy options, which is about 16% of the world’s energy consumption and mostly met by biomass, only a paltry 0.04% is accredited to solar. First and second generation solar cells offer mature technologies for applications. The most important difficulty with regards to integration with structures is not only the additional cost, but also the lack of sufficient knowledge in managing the available energy smartly and efficiently. The incorporation of PV as a part of building fabric greatly reduces the overall costs compared with retrofitting. BIPV (Building Integrated photovoltaic) is a critical technology for e...