Marin Rusu

Metal-Free Photocatalytic Graphitic Carbon Nitride on p-Type Chalcopyrite as a Composite Photocathode for Light-Induced Hydrogen Evolution

Recently, it has been shown that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. We present herein the preparation and characterization of graphitic carbon nitride (g-C(3)N(4)) films on p-type semiconducting CuGaSe(2) chalcopyrite thin-film substrates by thermal condensation of a dicyandiamide precursor under inert-gas conditions. Structural and surface morphological studies of the carbon nitride films suggest a high porosity of g-C(3)N(4) thin films consisting of a network of nanocrystallites. Photoelectrochemical investigations show light-induced hydrogen evolution upon cathodic polarization for a wide range of proton concentrations in the aqueous electrolyte. Additionally, synchrotron radiation-based photoelectron spectroscopy has been applied to study the surface/near-surface chemical composition of the utilized g-C(3)N(4) film photocathodes. For the first time, it has been shown that g-C(3)N(4) films coated on p-type CuGaSe(2) thin films can be successfully applied as new photoelectrochemical composite photocathodes for light-induced hydrogen evolution.

High-Efficient ZnO/PVD-CdS/Cu(In,Ga)Se2 Thin Film Solar Cells: Formation of the Buffer-Absorber Interface and Transport Properties

For preparation of ZnO/CdS/Cu(In,Ga)Se 2 solar cells, physical vapor deposition (PVD) was employed to deposit CdS buffer layers in ultrahigh vacuum on Se-decapped absorber surfaces, thus realizing an all ‘dry fabrication process of the device. An 14.1% total area and 14.5% active area efficient ZnO/CdS/Cu(In,Ga)Se 2 solar cell under AM1.5 conditions was achieved after annealing the as-prepared solar cells in air. Kelvin probe force microscopy (KPFM) measurements were carried out in-situ to monitor the initial growth of the CdS buffer layer on the absorber, as well as its electronic properties, in particular, the work function. It was observed that the PVD-CdS growth is initially inhibited at the absorber grain boundaries. Quantum efficiency measurements allowed us to suppose that during the initial growth stage a passivation of the grain boundaries occurs. The latter explains the higher short-circuit currents of the cells with PVD-CdS compared to their references with CdS grown by chemical bath deposition (CBD). The beneficial effect of the annealing seems to originate from a formation of a region with higher band gap than that of the absorber bulk and inverted conductivity type at the absorber surface, close to the CdS/Cu(In,Ga)Se 2 interface, leading to a dramatic change in the electronic transport properties and finally, to a significant enhancement of the open-circuit voltage. Annealing of the ZnO/PVD-CdS/Cu(In,Ga)Se 2 solar cells provides formation of PVDCdS/ Cu(In,Ga)Se 2 interface with properties similar to that of reference samples with CBD-CdS.

Work Function Homogeneity of Monolayer Passivated ITO Surfaces for Organic Solar Cells

The ITO transparent electrode surface is passivated either by organic quinoline molecules or by ions of periodic and phosphoric acids for organic solar cells. Passivated surfaces are investigated by means of Kelvin probe force microscopy.

Photovoltaic structures ITO/SiO х / n -Si of increased efficiency

Structures ITO/SiOх/n-Si are fabricated by pulverization of solutions of indium and tin chlorides on the (100) surface of silicon wafers with resistivity 4.5 Ω cm. The influence of the state of the Si surface on the efficiency of structures as photoelectric converters is investigated. It is shown that structures with an unetched surface of silicon wafers are the most efficient. Solar cells based on studied ITO/SiOх/n-Si structures with an inverse layer demonstrate an efficiency close to 16% in AM 1.5 conditions.

Solar Cells prepared with Spray-ILGAR Indium Sulfide buffer layers on Cu(In,Ga)Se 2 Absorbers

Indium sulfide buffer layers deposited by the Spray-Ion Layer Gas Reaction (Spray-ILGAR) technique have recently been used with Cu(In,Ga)(S,Se) 2 absorbers giving cells with an efficiency equal to the cadmium sulfide references. In this paper we show the first results from cells prepared with Cu(In,Ga)Se 2 absorbers (sulfur free). These cells reach an efficiency of 13.1% which remains slightly below the efficiency of the cadmium sulfide reference. However, temperature dependant current-voltage measurements reveal that the activation energy of the dominant recombination mechanism remains unchanged from the cadmium sulfide buffered cells indicating that recombination remains within the space charge region.