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Turnu Măgurele, Romania

Ghica C.,National Institute of Materials Physics Bucharest | Ion L.,University of Bucharest | Epurescu G.,National Institute of Lasers | Nistor L.,National Institute of Materials Physics Bucharest | And 2 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2010

Due to its wide band-gap (ca. 3.4 eV), ZnO is a possible candidate material to be used as transparent electrode for a new class of photovoltaic (PV) cells. Also, an increased interest for the photovoltaic properties of several organic monomers and polymers (merocyanines, phthalocyanines and porphyrins) was noticed, because of their high optical absorption in the visible region of the spectrum allowing them to be used as potential inexpensive materials for solar cells. Preparation and properties of CuPc (copper phthalocyanine) based photovoltaic cells using ZnO thin films as transparent conductor electrodes are presented in this paper. ZnO layers are grown by pulsed laser deposition, while the organic layers are obtained by thermal evaporation. Structural characterization is performed by electron microscopy. Optical and transport properties of the mutilayered structures are obtained by electrical and spectra-photometric measurements. The influence of the ZnO-polymer interface on the external quantum efficiency (EQE) of the photovoltaic cell is clearly evidenced by our measurements. Copyright © 2010 American Scientific Publishers. All rights reserved. Source


Nistor L.C.,National Institute of Materials Physics Bucharest | Ghica C.,National Institute of Materials Physics Bucharest | Kuncser V.,National Institute of Materials Physics Bucharest | Pantelica D.,Horia Hulubei National Institute of Physics and Nuclear Engineering | And 3 more authors.
Journal of Physics D: Applied Physics | Year: 2013

Highly textured ZnO thin films were implanted with Co ions at fluences of 1 × 1016 and 1 × 1017 ions cm-2. Although their microstructure observed by analytical high-resolution electron microscopy was very different, SQUID magnetometer measurements showed qualitatively similar magnetic properties. In the low-fluence film, only small modifications, such as a slight amorphization, planar defects or very small (<1-1.5 nm) Co clusters, were hardly observable. Implantation at a higher fluence led to important changes in the film structure: heavy amorphization and metallic Co precipitates were identified by electron diffraction, energy dispersive x-ray spectroscopy (EDS), electron energy loss spectroscopy and scanning transmission electron microscopy spectrum imaging. EDS microanalysis additionally revealed the presence of ∼2 at% Co atoms that were likely dissolved in the ZnO lattice at the atomic level. No Co oxides or other secondary oxide phases were detected. For both implanted samples, the dimensions of Co precipitates were below the superparamagnetic limit at room temperature. Thermo-magnetization curves and magnetic hysteresis loops measured in the temperature range from 5 to 300 K indicated two superimposed magnetic regimes, one predominant above 50 K and the other below 50 K. We analysed the possible mechanisms and quantitative contributions to explain the observed magnetic behaviour at low and room temperature. © 2013 IOP Publishing Ltd. Source

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