Boateng Onwona-Agyeman

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.

Triboluminescence of ZnS:Mn Films Deposited on Quartz Substrates with ZnO Buffer Layers

We have investigated the effect of ZnO films used as buffer layers on the triboluminescence (TrL) intensity of ZnS:Mn thin films on quartz substrates using the RF magnetron sputtering method and annealing technique. Highly oriented ZnO film was first deposited on quartz glass substrate and then the ZnS:Mn film was successfully deposited on the highly oriented ZnO film. By annealing at 5% H2 in Ar ambient, the crystallinity of both ZnO and ZnS:Mn films was improved. It was found that the addition of the ZnO buffer layer greatly improves the TrL intensity of the ZnS:Mn films.

An Abnormal Temperature Dependence of Conductivity in Fullerene Solids

An abnormal temperature dependence of conductivity has been observed in some fullerene solids, C60, C70, and C60H36 within the temperature range 400–500 K. The temperature dependent conductivity measurements of these fullerene solids with various molecular diameters and moments of inertia indicate that the abnormal conductivity involves a molecular rotation effect in the fullerene solids. Conductivity measurements of the C60 solid samples prepared using various pressures indicate that the abnormal conductivity is also related to a variation of the energy band structure. We are proposing a model to explain this abnormal conductivity observed as that, a reversible annealing effect results in the releasing or trapping of holes in the deep energy levels induced by lattice defects. The contribution of these holes leads to the abnormal variation in the conductivity with temperature.

Properties of Charge Carrier Transport in Au/Phenyl C61 Butyric Acid Methyl Ester/Au Structure

The properties of charge carrier transport through the Au/phenyl C61 butyric acid methyl ester/Au (Au/PCBM/Au) structure are studied by measuring DC currents passing through the structure at various temperatures and in the presence of an external electric field. Temperature- and field-strength dependent conductivities show that the energy band gap of the PCBM crystalline solid is 1.70 eV, and this value depends on the pressure during its preparation. There is a thermally activated process that controls the carrier mobility of this PCBM solid. We found out that its activation energy is influenced by the external electric field, and it increases with increasing field strength. The activation energy increases from 2 to 110 meV corresponding to a variation of the field strength from 50 to 1000 V cm-1. Theoretical calculation shows that the magnitude of the potential barrier for carrier transport through the structure increases only from 2 to 7 meV in the same field strength range owing to the Schottky effect on the Au/PCBM interface. Therefore, the field-strength-dependent mobility plays a more important role than the Schottky effect on the carrier transport through the structure.