Search

This contribution demonstrates density functional theory calculations on the optoelectronic properties of monoclinic CuO under high pressures up to 15 GPa. In this account, the experimentally measured indirect band gap energy value of 1.41 eV has theoretically been predicted by tuning the Hubbard parameter (U) values for the partial electronic states. The values of the Hubbard parameter correspond to UCu-3d = 8 eV and UO-2p = 4.5 eV. The electronic and optical characteristics were examined under applied pressure and the results reveal development in the band gap values with increasing pressure from 1.41 to 2.01 eV. Total and projected density of states for the adopted pressures have been provided and displayed that the major contribution in the valance and conduction bands comes from O-2p and Cu-3d electronic states, respectively. The plotted reflectivity data suggest high optical reflectivity magnitudes relatively in the ultraviolet area. The investigated systems under variant pressures manifest rather an excellent absorption coefficient in the ultraviolet area, pushing them to be employed in solar cell technologies. Our analyzed results of the wavelength-dependent electrical conductivity of the investigated materials confirm the absorptivity behavior in the ultraviolet and small part of visible region of electromagnetic waves (EMW). Finally and most importantly, our obtained results of loss functions for the entire surveyed systems reveal a slight energy loss in a range of EMW, including ultraviolet and visible regions. [ABSTRACT FROM AUTHOR]

Sol-gel derived CuCo-oxide coatings as solar selective surfaces, synthesized onto aluminium substrates at various annealing temperatures, are analysed by correlating their structural, chemical bonding states, and surface morphological topographies. As the annealing progressed, all the coatings displayed a Cu 0.56 Co 2.44 O 4 (ICSD 78-2175) phase with preferential orientation along (400) reflection plane. Rietveld refinement of X-ray diffraction (XRD) data indicate that residual stress and microstrains developed around the coating surfaces are reduced resulting in mechanically stable thin films. Enhancement of the crystallite size and preferred orientation of the surface were confirmed via XRD, field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM) analysis. X-ray photoelectron spectroscopy (XPS) analysis shows tetrahedral, octahedral and mixed states of Cu and Co ions with a stable atomic ratio of Co/Cu, and an increase of O and C contents but no metal-carbon bonding on the surface of materials. Optical reflectance investigations indicated that solar selectivity of the coatings increased from 3.81 to 24 as the annealing temperature reached up to 500 °C. [ABSTRACT FROM AUTHOR]