Malle Krunks

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.

Composition of CuInS2 thin films prepared by spray pyrolysis

CuInS 2 films were prepared by spray pyrolysis technique using CuCl 2 , InCl 3 and SC(NH 2 ) 2 as initial chemicals. The content of Cl, O, C and N impurities in sprayed CuInS 2 films were measured by EDS, WDS, RBS and organic elemental analysis. The growth temperatures of 260-280°C result in Cl, C, N content of 8 mass% and the impurity phases contain SCN, CN, NH, SO 4 groups as identified by FTIR. The increase in the growth temperature up to 380°C decreases the concentration of Cl, C, N to 1-2 mass%, concurrently leading to oxidation of inorganic and organic phases resulting in O content of 16.7 at.%. The content of impurities originated from precursors is mainly controlled by the growth temperature and in less extent by the Cu/In ratio in spray solution as Cu-rich solutions result in the films with reduced content of organic residues. Thermal treatments in reducing atmospheres at 450°C improves the crystallinity of the films while annealing in flowing H 2 effectively reduces the content of Cl and O impurities.

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.

Photoluminescence of spray pyrolysis deposited ZnO nanorods

Photoluminescence of highly structured ZnO layers comprising well-shaped hexagonal rods is presented. The ZnO rods (length 500-1,000 nm, diameter 100-300 nm) were grown in air onto a preheated soda-lime glass (SGL) or ITO/SGL substrate by low-cost chemical spray pyrolysis method using zinc chloride precursor solutions and growth temperatures in the range of 450-550°C. We report the effect of the variation in deposition parameters (substrate type, growth temperature, spray rate, solvent type) on the photoluminescence properties of the spray-deposited ZnO nanorods. A dominant near band edge (NBE) emission is observed at 300 K and at 10 K. High-resolution photoluminescence measurements at 10 K reveal fine structure of the NBE band with the dominant peaks related to the bound exciton transitions. It is found that all studied technological parameters affect the excitonic photoluminescence in ZnO nanorods.PACS: 78.55.Et, 81.15.Rs, 61.46.Km

ZnO Nanorods via Spray Deposition of Solutions Containing Zinc Chloride and Thiocarbamide

In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous solutions containing ZnCl2and thiocarbamide (tu) at different molar ratios. It has been observed that addition of thiocarbamide into the spray solution has great impact on the size, shape and phase composition of the ZnO crystals. Obtained layers were characterized by scanning electron microscopy (SEM) equipped with energy selected backscattered electron detection system (ESB), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). Small addition of thiocarbamide into ZnCl2solution (ZnCl2:tu = 1:0.25) supports development of significantly thinner ZnO nanorods with higher aspect ratio compared to those obtained from ZnCl2solution. Diameter of ZnO rods decreases from 270 to 100 nm and aspect ratio increases from ∼2.5 to 12 spraying ZnCl2and ZnCl2:tu solutions, respectively. According to XRD, well crystallized (002) orientated pure wurtzite ZnO crystals have been formed. However, tiny ‘spot’—like formations of ZnS were detected on the side planes of hexagonal rods prepared from the thiocarbamide containing solutions. Being adsorbed on the side facets of the crystals ZnS inhibits width growth and promotes longitudinalc-axis growth.

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.

Nature of the native deep localized defect recombination centers in the chalcopyrite and orthorhombic AgInS2

We studied the deep photoluminescence (PL) emission in polycrystalline chalcopyrite and orthorhombic AgInS2. In both phases several PL bands were detected at 8 K. On the energy scale these deep PL bands are positioned according to a regular pattern. This is explained as being due to electron-hole recombination within very close deep donor-deep acceptor pairs, with different distances between donor and acceptor defects. The deep donor defect is an interstitial silver Agi and the native deep acceptor defect appears to be situated at the Ag or In place. The two different crystal modifications also cause slightly different distances between donor and acceptor defects in the AgInS2 lattice and, as a result of this, different spectral positions of the deep PL bands. It is shown that these deep localized donor–acceptor pairs can be reasonably efficient radiative recombination centers up to distances of 5.3 A between the deep donor and the deep acceptor and, thus, up to six distinct deep PL bands are visible in A...

Study of zinc thiocarbamide chloride, a single-source precursor for zinc sulfide thin films by spray pyrolysis

Thermal decomposition of the title compound, Zn(tu)2Cl2 (tu=thiourea), was studied up to 1200°C in dynamic inert (N2) and oxidative (air) atmospheres using simultaneous TG/DTA techniques. In addition, XRD and IR were employed ex situ to resolve the reaction mechanism and products. Cubic ZnS (sphalerite) is formed below 300°C in both atmospheres and is observed until 760°C, whereafter it transforms in nitrogen to the hexagonal ZnS (wurtzite). EGA by FTIR revealed the complexity of the decomposition reactions involving also the evolution of H2NCN, which reacts to form hexagonal ZnCN2 as revealed by an XRD analysis.