Akinori Konno

Dye-sensitized solar cell with the hole collector p-CuSCN deposited from a solution in n-propyl sulphide

Abstract A method is devised for the deposition of CuSCN on ruthenium bipyridyl dye coated nanocrystalline TiO2 films from a solution in n-propyl sulphide. The dye-sensitized solid state photovoltaic cell formed was found to yield higher short-circuit photocurrent, open-circuit voltage and efficiency compared to the cells made with CuSCN by other deposition techniques. Factors affecting the stability of the cell are investigated.

Enhanced Efficiency of a Dye-Sensitized Solar Cell Made from MgO-Coated Nanocrystalline SnO2

Nanocrystalline SnO2-based dye-sensitized photoelectrochemical solar cells have very low open-circuit voltages of 325–375 mV and efficiencies of ~ 1%. However, on coating the SnO2 crystallites with a thin film of MgO, the voltage and efficiency are increased to 650–700 mV and ~ 6.5%, respectively. Evidence is presented to show that the photoexcited dye on the outer MgO shell could tunnel electrons to SnO2 and that the low probability of reverse tunneling suppresses recombinations, thus increasing the efficiency. An explanation is also given as to understand why dye-sensitized TiO2 cells are more efficient than those made from SnO2 alone.

Suppression of recombinations in a dye-sensitized photoelectrochemical cell made from a film of tin IV oxide crystallites coated with a thin layer of aluminium oxide

A dye-sensitized photoelectrochemical cell consisting of a film of SnO2 crystallites coated with ultrafine particles of Al2O3 generates an exceptionally high open-circuit voltage as compared to a cell made only from SnO2. Al2O3 coating on SnO2 improves the efficiency and the fill factor while delivering reasonably high photocurrents. Photoexcited dye molecules on Al2O3 injects electrons into the conduction band of SnO2 via tunnelling through the Al2O3 barrier. Suppression of recombinations of electrons with the dye cations and the acceptors at the electrolytic interface build up the quasi-Fermi level in SnO2 with an impressive increase of the open-circuit voltage.

Dye-sensitized composite semiconductor nanostructures

Understanding of the charge transport and recombination mechanisms of dye-sensitized solar cells based on semiconductor nanostructures is essential for the improvement of their performance. A great deal of information on these systems have been obtained from studies on a single material (mostly TiO2 and to a lesser extent ZnO and SnO2). We have conducted extensive measurements on composite dye-sensitized nanosturctures and found that the composite systems possess unusual properties. Dye-sensitized photoelectrochemical cells made from nanocrystalline 7lms of some materials (e.g., SnO2) yield comparatively small open-circuit voltages and energy and quantum conversion e9ciencies, despite excellent dye-semiconductor interaction. However, on deposition of ultra-thin shells of insulators or high band gap semiconductors on the crystallites, a dramatic increase in the above parameters is observed. Outer shells were found to have insigni7cant or in most cases a negative e;ect on TiO2 7lms. We explain the above 7ndings on the basis of vast di;erences in the leakage rates of trapped electrons in di;erent materials which is sensitive to the e;ective electron mass. Electrons injected to the conduction band in dye-sensitization enter into shallow traps from which they get thermally reemitted to the conduction band. The building up of the electron quasi-fermi level and transport depends on this process. The spread of the hydrogenic wave function of a trapped electron increases inverse exponentially with the e;ective mass so that the electron leakage and their recombination with acceptors ‘outside’ become severe when the crystallite size is comparable to the Bohr radius of the trapped electron. Such recombinations are e;ectively suppressed by deposition of thin 7lms on the crystallites. Excited dye molecules anchored to the outer shell injects electrons to the conduction band via tunneling. ? 2002 Elsevier Science B.V. All rights reserved.

Sensitization of Nanocrystalline SnO2 Films with Indoline Dyes

Using newly synthesized indoline dyes as sensitizers for photoelectrochemical solar cells based on SnO2 nanocrystalline films, an energy conversion efficiency of 2.8% is achieved, compared with 1.2% for ruthenium bipyridyl dye (N-719) under the same experimental conditions. It is suggested that the formation of nonquenching aggregates and the better passivation of surface states on SnO2 by indoline dyes are instrumental factors in giving a higher efficiency for the cell sensitized with this dye.

Electrolytic partial fluorination of organic compounds ☆: Part 44. Anodic gem-difluorodesulfurization using triarylamine mediators

Indirect anodic gem-difluorodesulfurization of dithioacetals was successfully carried out using triarylamine mediators to provide gem-difluoromethylene compounds in moderate to good yields.

Dye-sensitized solid-state photovoltaic cells: suppression of electron-hole recombination by deposition of the dye on a thin insulating film in contact with a semiconductor

The heterojunction n-SnO2/Ru-dye/p-CuI prepared by deposition of the ruthernium bipyridyl dye on a meso-porous film of SnO2 followed by deposition of p-CuI was found to be inactive with respect to visible light photoresponse and dark current rectification. However, n-SnO2/Al2O3/Ru-dye/p-CuI where the dye is coated on a thin film on Al2O3 first deposited on SnO2, delivered a short-circuit current density of 1.7 mAcm−2 and an open-circuit voltage of 350 mV, behaving as a dye-sensitized solid-state photovoltaic cell. This result is explained as a transfer of energetic electrons released by excitation of the dye molecules to the conduction band of SnO2 via tunneling across the thin layer of Al2O3. The implications of the result on suppression of recombination in dye-sensitized photovoltaic cells are discussed.

Electrolytic partial fluorination of organic compounds. Part 27. Regioselective anodic monofluorination of 2-substituted 1,3-dithiolanon-4-ones using Et4NF·4HF and Et3N·3HF

Abstract Highly regioselective anodic monofluorination of 2-substituted 1,3-dithiolan-4-ones was successfully carried out by using novel supporting electrolyte, Et 4 NF·4HF while a conventional supporting electrolyte, Et 3 N·3HF gave poor yields and/or low current efficiencies owing to severe passivation of the anode during the electrolysis.

Li-Ion Conductivity of Aluminate and Borate Complex Polymers Containing Fluoroalkane Dicarboxylate

Single-ion conducting polymer electrolytes which contain fluoroalkane dicarboxylate substituted aluminate or borate backbone and two methoxy [oligo (ethyleneoxide)] side chains directly bonded to the ate complex centers (aluminum, borate, etc.) were prepared. Borate polymers containing a long ether chain (n = 11.8) exhibited high ionic conductivity (10 -5 S cm -1 at 30°C) and high electrochemical stability. The relationship between polymer structure and ionic conductivity is discussed with the partial charge density on oxygen atoms of the ate complex from the calculations in MOPAC.

Effect of strong magnetic fields on the photocurrent of a poly(N-methylpyrrole) modified electrode

Abstract The photoelectrochemical behavior of poly(N-methylpyrrole) in strong magnetic fields was investigated. When the magnetic field was increased from 0 to 3, then to 7 T, the intensity of the initial photocurrent of the poly(N-methylpyrrole) (PPy) modified electrode was increased in 0.1 M NaClO4+acetonitrile solution. When dichloromethane solution containing Bu4NClO4 was used as an electrolyte, the dependence of the photocurrent on the magnetic field was also observed not only in the initial but in the second and third photocurrent responses. Interestingly, the photocurrent of the PPy modified electrode increased not only with the magnetic field, but also by each repetition of measurement. In repetitive measurements of the photocurrent strong magnetic fields obviously accelerated the increasing photocurrent compared with that in a zero magnetic field. Thus, the photocurrent of a conducting polymer-modified electrode can be controlled by a strong magnetic field. This is the first example of a magnetic field effect on the photoelectrochemistry of a conducting polymer.