SOLID STATE PHOTOELECTROCHEMICAL CELL BASED ON DYE SENSITIZED TiO2 AND POLYMER ELECTROLYTE COMPLEXED WITH I3¯/I¯

A solid state photoelectrochemical solar energy conversion device based on nanocrystalline-TiO2 sensitized with Di-Tetrabutylammoniumcis-bis(isothiocyanato)bis(2,2’-bipyridyl-4,4’-dicarboxylato)-ruthenium(II) (N719) dye has been constructed and characterized. The current density–voltage characteristics in the dark and under white light illumination and action spectra under monochromatic illuminations have been studied. The following device parameters were obtained when the potential is scanned: an open circuit voltage of 762 mV and a short circuit current density of 33 μAcm-2 at light intensity of 100 mWcm-2; the IPCE percentage obtained was 1.7% at 330 nm. The dependence of the short-circuit current density and an open circuit voltage on the incident light intensity and illumination time have also been studied. The results of time dependence study show that the steady state Jsc and Voc values are consistent with those obtained from the J–V curve

CHROMIC TRANSITIONS IN PHENYL-SUBSTITUTED POLYTHIOPHENES

The solvatochromic and thermochromic behaviours of phenyl-substituted polythiophenes were studied. The pristine polymers, upon dissolution in chloroform, exhibited blue-shifted absorption. The solid films of the polymers showed significant blue-shifted as well as red-shifted absorptions when heated. While the addition of methanol to the chloroform solutions of the polymers caused dramatic chromic changes and development of red-shifted spectra for many of the polymers investigated, the symmetrically phenyl-substituted and sterically hindered polymer (polymer 1) does not show significant changes. These chromic behaviours have been examined in terms of substituent effects and attempt has been made to explain these effects by calculating the energy barrier for rotation to a planar structure using the HF SCF method and 3-21G* basis set. KEY WORDS: Chromic transitions, Phenyl-substituted polythiophenes Bull. Chem. Soc. Ethiop. 2005, 19(2), 267-276

Synthesis, optical and electrochemical characterization of anthrancene and benzothiadiazole-containing polyfluorene copolymers

New solution-processable, anthrancene- and benzothiadiazole-containing polyfluorene copolymers (P1-P3) have been synthesized and characterized. The preparation and characterization of the corresponding blue light-emitting devices are also reported. Polymers P2 and P3 show high photoluminescence efficiency while polymer P2 does not show any significant light emission up to 8.0 V. The results show the need for balance of electron and hole transport in polymer light emitting diodes. KEY WORDS: Anthracene, Benzothiadiazole, Polyfluorene copolymers, Photoluminescence, Light emitting diode  Bull. Chem. Soc. Ethiop. 2006, 20(2), 309-317

Photoelectrochemical cells based on emeraldine base form of polyaniline

Photoelectrochemical cells (PECs) have been fabricated using the emeraldine base form of polyaniline (EB) as a photoactive material and Eu2+/Eu3+ redox couple in methanol as an electrolyte. A PEC with a structure: Glass/ITO/EB/electrolyte/Pt produces an open-circuit voltage (V OC) of -0.132 V and a short-circuit current (I SC) of 0.64 µA cm-2 under 50 mW cm-2 white light illumination from Xe lamp. In an effort to increase the photoresponse, a PEC with a structure: Glass/ITO/EB:Nc-TiO2/Electrolyte/Pt has been devised in which a composite film of EB and nanocrystalline TiO2 (Nc-TiO2) is used as a photoactive material. The cell shows a V OC of -0.205 V and an I SC of 105 µA cm-2 when illuminated under the same conditions

Hansen Solubility parameters and Green Solvents for Organic Photovoltaics

The determination and prediction of solubility behavior of organic semiconductors to use them is very important.[1] The concept Hansen solubility parameters is applied for the study. HSPs for PC61BM were determined using HSPiP software. In this experiment, we used 20 and 39 solvents in the first and second phases of the experiment respectively to determine HSPs for PC61BM. The results obtained were 18.23, 3.75, and 4.51MPa1/2 for dispersive, polar and hydrogen bonding for the first and 17.58, 3.73 and 4.79 MPa1/2 for the second respectively. These results were compared to HSPs of chloroform, Limonene and Benzaldehyde. Limonene is used for cleaning in the electronic and printing industries, and in paint as a solvent. [2] It was selected as a solvent to replace the chlorinated type solvents. (HSPs) of Limonene, with δD, δP and δH of 17.20, 1.8 and 4.3 MPa1/2 respectively, were obtained from the HSPiP list of solvents and the calculated Relative Energy Difference of 0.333 for Limonene to PC61BM suggested that limonene could be a good non-chlorinated for solution processing of fullerene-based polymer solar cells. The Limonene processed active layer in this work displayed a maximum power conversion efficiency of 3.19 % and our results suggest that Limonene would be a promising solvent for environment – friendly fabrication of polymer solar cells if more efforts is done to improve the power conversion efficiency

Photoelectrochemical solar energy conversion based on blend of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl) propyl-1-phenyl [6,6]C₆₁ (PCBM)

A solid-state photoelectrochemical solar energy conversion device based on blend of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C₆₁ (PCBM), and an amorphous poly(ethylene oxide) complexed with I₃^-/I^- redox couple has been constructed and characterized. The photoelectrochemical performance parameters of the device were compared with pure P3HT and P3HT:C₆₀ blend solid-state photoelectrochemical cell. The current density-voltage characteristics in the dark and under white light illumination and photocurrent spectra for front and backside illuminations have been studied. An open-circuit voltage of 140 mV and a short-circuit current density of 28.4 μA/cm² at light intensity of 100 mW/cm²; IPCE% of 1.52% for front side illumination (ITO|PEDOT) and IPCE% of 0.17% for backside illumination (ITO|P3HT:PCBM) at a wavelength of 510 nm were obtained. The dependence of the short-circuit current density and an open-circuit voltage on the light intensity and time have also been studied.DOI: http://dx.doi.org/10.4314/bcse.v26i2.1

<b>The photoresponse behavior of a MEH-PPV sensitized titanium dioxide photoelectrochemical cell</b>

A solid-state photoelectrochemical cell based on polymer-sensitized nanocrystalline titanium dioxide (nc-TiO2) was constructed and studied for its photoresponse behavior. Poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and Poly[oxymethylene-oligo(oxyethylene)] (POMOE), complexed with I3-/I- redox couple were used as a polymer-sensitizer to TiO2 and as a solid polymer electrolyte, respectively. The device produced a short-circuit current of 0.145 mA/cm2, and an open-circuit voltage of 410 mV under the irradiance of 100 mW/cm2. The power conversion efficiency and the fill factor were 0.03 % and 0.5, respectively. The monochromatic induced photon-to-current conversion efficiencies for backside (ITO/nc-TiO2/MEH-PPV) and for front side (ITO/PEDOT) illuminations were 1.8 % and 1.4 %, respectively

Structure and molecular interactions in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide ionic liquid/carbonate co-solvents -– combined DFT and molecular dynamics study.

Both density functional theory (DFT) and molecular dynamics (MD) based on classical force field were used to provide both structural and electronic insight into the multifold interactions occurring in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid in the presence of ethylene carbonate and dimethyl carbonate co-solvent mixtures which are currently being targeted for applications in next-generation Li-ion battery electrolytes. In order to give a visual understanding of the molecular interactions, the structures of cations, anions, and cation - anion ion pairs were systematically studied using DFT calculations. The nature of hydrogen bond interactions in a series of ion pair conformers have been thoroughly discussed by analyzing the interaction energies, stabilization energies and natural orbital analysis of the ion pair conformers. Multiple but weak C ̶ H---O/N hydrogen bonds and anion donor π*C–N interactions have been observed. Charge transfer occurs mainly from the lone pairs of oxygen and nitrogen atom to the σ-type anti-bonding orbital of the C–H bonds and π-type anti-bonding orbitals of N ̶ C bonds. According to the MD study, the addition of carbonate co-solvents into the pure ionic liquid creates a more structured system than the pure ionic liquid. The coordination of the O/N atoms of the bis(trifluoromethylsulfonyl)imide anion to the most acidic H atom of 1-ethyl-3-methylimidazolium cation showed a marked decrease with increase in carbonate concentration indicating that the C ̶ H---O/N hydrogen bond interaction is reduced by the presence of high carbonate content. Furthermore, in the pure ionic liquid, adjacent cations are almost exclusively located on top and below the ring cation, whereas the anions mainly coordinate to the cation within the ring plane. The addition of large amount of carbonate co-solvents disturb the original near ordering which is found in the pure ionic liquid. Key words: electrolyte, Li-ion, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ethylene carbonate, dimethyl carbonate