• Energy Research

Abstract Below we present semiempirical modeling of conceptually new three-sublayer photoanode, composed of Absorber, Grading and Barrier sublayers, for highly efficient photoelectrochemical water dissociation. The modeling resulted into Absorber (Sub-A) made of Cd 0.55 Zn 0.45 O due to its favorable positions of the band extrema to the water splitting potentials and a band gap ~2.0 eV. The Grading layer (Sub-G) was composed of Cd x Zn 1−x O with a gradual decrease of x across the profile, changing from 0.2 to 0.55, aiming to photon absorption from 2.0 to 3.0 eV. At the same time, Sub-G furnishes the profile with an implanted electrical field that improves the hole-transport. The electron Barrier layer (Sub-B) deposited above the Sub-A, was engineered to provide 1 eV high barrier in the conduction band. It comprised of a 50 nm thick Ni 0.4 Cd 0.6 O film with E g ~3.0 eV with a valence band aligned to the one of the Sub-A, providing a barrier-free hole-flow. In this paper, we provide evidence that the proposed three-sublayer concept clearly represents a new paradigm for an improved efficiency for photocatalytic water dissociation. The highest photocatalytic activity of the optimized profile was achieved with an optimized electrolyte: 87% 1 M K 2 HPO 4 and 13% 1 M Na 2 SO 3 (known to act as a hole scavenger or sacrificial agent) at pH=10. A noteworthy feature of this study is that under optimized profile parameters and customized electrolyte conditions the photocurrent yields increased from ~0.05 mA/cm 2 to ~20 mA/cm 2 at +1.2 V for visible light. The observed Incident Photon-to-Current Efficiency (IPCE) was about 50% measured at a photon energy of 3 eV.

Abstract The aim of this work is to attract the attention of the scientific workers in the field of PV conversion of solar energy to SnS polycrystalline thin film as a candidate for construction of cheap solar cells, since it posseses similar photoelectric properties as polycrystalline silicon, but it can be produced on any kind of substrate, by simple, economic and environmentally approved technique. By the use of the method of chemical deposition from two separate solutions, complete preparation of three types of cells was done. All of them use SnS as base absorbing layer, with a difference in the window layer electrode. The first one has CdO, the second one has Cd 2 SnO 4 thin film window electrode, both prepared by the chemical deposition method. The third cell was purely Schottky barrier cell in which the window electrode was SnO 2 :F, prepared by spray pyrolysis. The I – V , C – V and spectral characteristics were registered and the conclusion was drawn that the best performances has shown the cells with Cd 2 SnO 4 film as a window electrode.

Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges.

Abstract Enhancement of the optical and electrical properties of Cd-rich NixCd1−xO alloys was achieved through an electrochemical procedure – their biasing at a constant negative potential into an electrolyte. Depending on the conductivity of the film (correlated to x), the films changed their color from transparent-yellowish to black. For a certain bias, the coloration became permanent and irreversible. Electron concentration for some samples increased for better than two orders of magnitude upon the coloration, while as the mobility decreased for a factor of 2–10. Rutherford Back Scattering (RBS) analysis revealed oxygen deficiency for the colored samples. The XRD analysis showed that the coloration could be associated to a partial reduction of CdO2 to CdO. XPS analysis suggested complex red-ox transitions of the two Ni and two Cd-oxides within the alloy. Ni2p electrons suggested that a partial NiO (transparent) transition to Ni2O3 (black) is likely the responsible process for the occurrence of the intensive light trapping. Since the NixCd1−xO band gap is tunable with x, one may conclude that this electrochemical procedure is motivating for tuning/modification/enhancement of the both, the absorption and conductivity of NixCd1−xO films for their possible application as integrated film photoanodes (TCO and PEC cell in one) within a hybrid water splitting device.

Abstract Thin cuprous oxide electrochromic films on the transparent conductive electrodes were prepared by chemical electroless method. The films cycled in K + -based electrolyte revealed typical red-ox peaks with higher intensity compared to those in the Li + and the Na + -based electrolytes. The durability of the cuprous oxide due to cycling into LiClO 4 was about 60 cycles. The thermal treatment of the films invoked decrease in red-ox peak intensity, and thus deterioration in the electrochromic properties. The response time of the coloration and bleaching to an abrupt voltage change from −4.5 to +4.5 V and reverse was found to be in the range of about 10 s. The maximum light intensity modulation ability of the films, as the AM1.5 spectrum is taken for an input, was calculated to be about 65%.

Abstract CdS : Ag thin films were deposited by the chemical deposition method (solution growth), on SnO2 thin transparent electrodes, to obtain n-type window layer for PV-cell. CdS thin films were doped with silver by an ion-exchange process in a neutral 0.025 M thiosulphate Ag-complex solution. Best results were achieved at immersion times of 20–30 s at room temperature. For the sake of comparison, the doping was performed on 1 2 of the substrate surface, while the remaining part was left undoped. SnSx thin layer was deposited on the top of such a n-type layer prepared in the same way the p-type layer was selected due to its simplicity of preparation and the possibility for variation of the band gap (Eg), by varying x in the compound. Ohmic contact was produced by graphite paste backelectrodes. Two different types of PV cells were produced on the same test sample, SnO2/CdS : Ag–SnSx/C and SnO2/CdS–SnSx/C, in order to study the influence of the Ag doping of CdS, on the PV cell parameters. Dark and light I–V characteristics were recorded for the two types of cells at several different light intensities. Considerable enhancement of all cell parameters, efficiency (η), fill factor (FF), diode factor (a), short-circuit current (Isc), etc., was observed on the CdS : Ag-based sample. Spectral sensitivity in VIS-NIR part of the spectrum, recorded on the two types of cells, showed an improvement on the CdS : Ag-based PV cell.