E. Mellikov

Zinc oxide thin films by the spray pyrolysis method

Abstract Undoped and In-doped ZnO thin films have been prepared on glass substrates from solutions of Zn(CH3CO2)22H2O in a mixture of deionized water and isopropyl alcohol by spray pyrolysis. Their optical, morphological and structural qualities have been studied and the effect of the preparation conditions discussed. It was shown that the main factors determining the parameters of ZnO films are the growth temperature and the indium concentration. The growth temperatures of 625–675 K, indium doping levels of 1–1.5 at.% and precursor concentrations of 0.1–0.2 mol 1−1 are preferable to achieve ZnO films with optical and structural qualities as required for solar cell applications.

Structural and optical properties of sprayed CuInS2 films

Abstract Polycrystalline CuInS 2 thin films have been prepared by spray pyrolysis of aqueous solution of copper chloride, indium chloride and thiourea onto heated glass substrates. It is shown that the parameters critical to structural and optical properties of sprayed CuInS 2 films are growth temperature and ion ratio of Cu/In in spraying solution. Excess of copper in starting solution promotes the recrystallization and growth of crystallites in the film. The X-ray diffraction patterns confirm that the use of copper-rich solutions reduces the temperature required for single-phase composition of CuInS 2 films from 380°C ( Cu/In =1 ) to 290°C ( Cu/In =1.25 ). The formation of CuInS 2 in spray process and chemical nature of additional phases in the films are discussed. Growth temperatures in the range of 320–380°C at Cu/In >1 are determined as optimal for depositing orientated in the (112) direction CuInS 2 thin films with chalcopyrite structure. Sprayed chalcopyrite CuInS 2 films have absorption coefficient ∼10 5 cm −1 in visible and red region of spectra and optical band gap 1.45 eV.

Composition and structure of CuInS2 films prepared by spray pyrolysis

Abstract CuInS2 thin films have been prepared by spray pyrolysis of an aqueous solution of CuCl2, InCl3 and thiourea onto heated glass substrates. The effect of the composition of starting solutions on the phase and chemical composition and the structure of sprayed films is studied. The Cu/In ratio in the films is higher than that in the solution. In-rich and S-rich solutions lead to the multiphase films with poor crystallinity according to X-ray diffraction. It was determined that organic phases as products of the thermal decomposition of thiourea ligand are present in the films at all used solution compositions. The formed organic secondary phases could be responsible for the formation of molten phase which together with copper sulphide act as recrystallisation agent during the growth of copper-rich films. The CuInS2 films, strongly orientated in the (112) direction with crystallites up to 300 nm in the matrix and with large crystals of some microns in agglomerated areas, are formed while the secondary phases segregated on the thin film surface.

Growth and recrystallization of CuInS2 films in spray pyrolytic process

Abstract It is shown that the structure, composition and surface morphology of chemically sprayed CuInS2 films depend on the growth temperature and copper to indium ratio in the spraying solution. In-rich films have flat surface but they are multiphase. The use of Cu-rich initial solutions leads to single-phase films with the rough surface morphology. The important role in the formation of these films plays segregation of molten phase of thermal decomposition products on the surface during the spray process. The possible crystal growth mechanisms in both types of CuInS2 thin films in the spray process are discussed.

Monograin layer solar cells

The paper presents results of studies directed towards the production of monograin powders of CuInSe for possible use in 2 solar cells preparation.The results concern the tailoring of chemical and defect composition of materials, development of the technology of manufacturing monograin layers (MGL) on the base of developed materials and the cleaning of open surfaces of the grains in the MGL by different mechanical, chemical and electrochemical methods.It is shown that up to now the low efficiency of MGL solar cells is associated with the chemical and defect composition of the monograin powder materials and with difficulties in cleaning the surfaces of the crystals in the MGL before depositing active contacts. 2003 Elsevier Science B.V. All rights reserved.

Gel-forming structures and stages of red algal galactans of different sulfation levels

Sol-gel transition processes of algal galactans were studied using cryofixation method in combination with freeze-drying and scanning electron microscopy (SEM) techniques. The structures formed in successive stages of gelling process upon cooling were rapidly frozen at defined temperature points and viewed by SEM. It was established that in the case of both types of gelling galactans investigated, a fine honeycomb-like network exists for a wide range of solution temperatures. The formation and structure of this network depends on the structural type, gelling stage, and concentration of the galactan in solution. The honeycomb suprastructures exist also in carrageenan and agarose sols (at temperatures considerably exceeding the gelling temperatures). An additional helical network formed showed different behaviour in the case of carrageenan and agar-type polysaccharides. In the gel-formation process, tightening of the network takes place in both types of galactan gels; the honeycomb structures persist in carrageenan (furcellaran) but not in agarose gels.

Energy of excitons in CuInS2 single crystals

High-quality single crystals of CuInS2, grown by the traveling heater method in an indium solvent, were characterized using photoluminescence (PL) and reflectance (RF) at temperatures from 4.2to300K. A number of well-resolved sharp excitonic peaks have been observed in the near-band-edge region of the PL and RF spectra at 4.2K. The lines at 1.536 and 1.554eV in the RF spectra were associated with A and (B,C) free-excitonic transitions, respectively. In the PL spectra the A exciton revealed a well-resolved splitting into two peaks at 1.5348 and 1.5361eV assigned to the lower and upper branches of exciton polariton, respectively. Other sharp lines were assigned to excitons bound at shallow impurities. The experimental temperature variation of the band gap was analyzed using the Bose–Einstein model. Two deeper bands in the PL spectra were identified as free-to-bound optical transitions followed by phonon replicas.

CuInSe2 Monograin Growth in CuSe-Se Liquid Phase

Isothermal growth of CuInSe2 monograin powders in molten CuSe-Se flux has been studied proceeding from Culn (1:1) alloy, Se and CuSe. The activation energy for linear crystal growth Ed = 0.28(±0.03) eV and the power of time dependence of crystal growth 1/n=0.27(±0.017) according to the equation: dm=At1/nexp (-Ed/kT) have been found. As a result homogeneous high-conductive (0.5 Ωcm) p-type CuInSe2 material (22.4 : 25.1 : 52.5) with single-crystalline grain structure and narrow-disperse granularity is synthesized from CuSe-Se solvent.

Copper sulfides by chemical spray pyrolysis process

The chemistry of formation of copper sulfide and copper indium disulfide films by the chemical spray pyrolysis process has been investigated. It was established that the formation of copper sulfide films by the spray process of water solutions of CuCl2 and SC(NH2)2 passes through the stage of formation of intermediate complex compound Cu(SCN2H4)ClH2O in the initial solution. Thermal behaviour studies in air exhibit rearrangement of the complex at temperatures higher than 210 °C with formation of copper sulfide. Copper oxide is the decomposition product at temperatures higher than 700 °C in air. CuInS2 is formed by the reaction between copper and indium sulfides.

Annealing effect for SnS thin films prepared by high-vacuum evaporation

Thin films of SnS are deposited onto molybdenum-coated soda lime glass substrates using the high-vacuum evaporation technique at a substrate temperature of 300 °C. The as-deposited SnS layers are then annealed in three different media: (1) H2S, (2) argon, and (3) vacuum, for different periods and temperatures to study the changes in the microstructural properties of the layers and to prepare single-phase SnS photoabsorber films. It is found that annealing the layers in H2S at 400 °C changes the stoichiometry of the as-deposited SnS films and leads to the formation of a dominant SnS2 phase. Annealing in an argon atmosphere for 1 h, however, causes no deviations in the composition of the SnS films, though the surface morphology of the annealed SnS layers changes significantly as a result of a 2 h annealing process. The crystalline structure, surface morphology, and photosensitivity of the as-deposited SnS films improves significantly as the result of annealing in vacuum, and the vacuum-annealed films are fo...