E. Koudoumas

Post-fabrication annealing effects in polymer-nanotube photovoltaic cells

We present a systematic study of the effects of post-fabrication annealing on the performance of photovoltaic devices that incorporate a photoactive donor–acceptor dispersed heterojunction system. Solar cells have been fabricated based on poly(3-octylthiophene) as donor (D) and single-wall carbon nanotubes as the electron acceptor (A) with a PEDOT:PSS hole transport layer. A post-fabrication annealing treatment was carried out at a temperature range of 40–200 °C. The best results were obtained at 120 °C; at this temperature the cell shows a short circuit current, Isc = 0.5 mA cm−2, an open circuit voltage, Voc = 0.75 V and a fill factor, FF = 0.6, resulting in a power conversion efficiency of η = 0.22% under AM 1.5 (100 mW cm−2) white light illumination. The annealing treatment led to a doubling of the power conversion efficiency. This was attributed to a better charge carrier transport in the polymer matrix and more effective charge separation and collection.

Electrochemical properties of vanadium oxide coatings grown by hydrothermal synthesis on FTO substrates

Vanadium oxide coatings were hydrothermally grown on fluorine doped tin dioxide glass substrates at 95 °C and further annealed at 100 and 300 °C. The coatings were characterized by X-ray diffraction, Raman spectroscopy, atomic force microscopy, UV-vis transmittance and cyclic voltammetry. Crystalline vanadium(V) oxide with the highest surface area ratio was observed for thermal treatment at 300 °C. In addition, the same sample presented the highest intercalation charge and enhanced durability compared with the others. The importance of achieving single-phase crystalline oxide for the improvement of the coatings performance was highlighted.

Hydrothermally grown β-V2O5 electrode at 95 °C

The hydrothermal growth of crystalline β-V2O5 microstructures was performed on fluorine doped tin dioxide glass substrates using oxalic acid to adjust the pH of the solution for various deposition periods. It was observed that the sample grown for 48 h at pH 2 exhibited the best electrochemical response in terms of the highest specific charge and capacitance, being 772 C g(-1) and 386 F g(-1) respectively. The importance of achieving high crystalline quality samples and increased surface area toward the improvement of the electrochemical performance of β-V2O5 is highlighted.

Polymer-nanotube composite mats with improved field emission performance and stability.

The results of electron field emission from single walled carbon nanotubes (SWCNTs) mats deposited on different composite films of SWCNTs and poly(3-octylthiophene) (P3OT) semiconducting polymer are presented. Three different structures were tested: (a) dense and sparse SWCNT mats on n+ -Si; (b) SWCNT mats on composite films with different SWCNT-P3OT ratios; (c) composite films with different SWCNT-P3OT ratios on n+ -Si. The experiments show that there is a critical SWCNT-P3OT concentration in which the field emission stability of SWCNT mats is remarkably improved with a small reduction in the emission threshold compared to the optimum pristine SWCNT film. The contribution of the composite film morphology as well as the role of polymer-nanotube interaction on the emission performance are evaluated. The physical mechanism behind the stability of composite field emitters is also discussed.

Precursor concentration effect on structure and morphology of ZnO for coatings on fabric substrates

Abstract ZnO is a versatile functional material that has a diverse group of growth morphologies. By controlling the growth kinetics, it is possible to change the growth behavior of ZnO structures. Growth of ZnO structures can be achieved in a cheaper way at low temperature using chemical growth techniques such as aqueous chemical growth, nonaqueous solution growth, sol gel and spray deposition. Up to date, there are quite few reports in the literature presenting state of art approaches of use of ZnO material onto textile substrates for several applications as antibacterial, deodorizing and UV protection, and none regarding any systematic approach of direct growth and optimization with respect to the textile support. The successful exploitation of ZnO particles for use in various technological applications requires the development of techniques for controlling its photocatalytic activity. The present contribution presents a study of precursor concentration effect on structure and morphology of ZnO for coatings on fabric substrates. ZnO particles were obtained by direct growth onto the respective substrate by aqueous chemical growth using suitable precursors for each growth and then characterized regarding their appearance, size and structure using microscopic techniques and X-ray diffraction.

Comparative study on field collected samples of aged silicon rubber composite coatings for high voltage insulators

Abstract : Pollution of high voltage (HV) insulators is a phenomenon with a considerable impact to the performance of transmission and distribution electrical networks. The use of composite materials and especially Silicone Rubber proved to be an efficient improvement, capable of suppressing the problem and diminishing the flashover probability. As a result ceramic insulators in transmission lines are replaced by insulators with composite housing, either HTV Silicone Rubber or LSR. In the case of HV substations however, the replacement of insulators is rather difficult, due to the complexity of the equipment and the corresponding financial cost. In this case the application of RTV Silicone Rubber is an equivalent alternative. The ceramic insulators are covered with a 0.5 mm RTV SIR coating which provides the advantages of composite insulators on a ceramic substrate. After installation the possible material lifetime, which is determined by the service conditions and the material formulation, is of primary concern. In Crete, a large scale application exists and coatings that exceed a service period of 10 years are still in operation. The present study focuses on the structural and morphological characterization of field collected composite insulators of various ages so that the degradation degree can be correlated with their service.