Single-phase Chalcopyrite Research Articles

Spray pyrolysis of CuInSe 2

Spray pyrolysis is a low-cost method of depositing thin films and is an economically attractive alternative to the vacuum deposition methods that have been used to produce stable CuInSe 2-based solar cells. Thermodynamic studies have shown that the preferred deposit from an aqueous solution of CuCl 2, InCl 3 and N,N-dimethylselenourea is CuInSe 2. Experimental studies have demonstrated that, under the proper conditions, single-phase chalcopyrite CuInSe 2 of 〈112〉 crystal orientation can be deposited with controlled resistivity and relatively high hole mobility.

Production of single phase chalcopyrite CuInSe2 by spray pyrolysis

Thin films (0.5–2 μ) of CuInSe2 were prepared by spray pyrolysis from solutions with various pH levels and initial Cu:In ratios, and in which the Cu source was either CuCl or CuCl2. The substrate temperature was varied between 225 and 300 °C. All films prepared with CuCl2 were chalcopyrite, while only Cu-rich CuCl based films exhibited this phase. The appearance of Cu2−xSe and/or Cu2/Se as a second phase was found to depend strongly on solution stoichiometry, pH, temperature, and substrate. Two layer structures consisting of a Cu-deficient layer on top of a Cu-rich layer were produced without the presence of any second phases on both glass and Mo-coated glass. This is the first time single phase chalcopyrite Cu-deficient layers have been fabricated by spray pyrolysis. A CuInSe2/CdS photovoltaic cell made from a single phase double layer filme on glass gave a Voc of 0.558 V after heat treatment. This Voc is higher than any reported to date. Absorption spectra have also been measured, and are found to improve when CuCl2 is used instead of CuCl.

Reactive sputtered copper indium diselenide films for photovoltaic applications

Single phase chalcopyrite CuInSe2 coatings have been deposited by reactive cosputtering from Cu and In planar magnetron sources operated in an Ar+H2Se working gas. Effective sputtering yields from the conditioned Cu and In targets were approximately 0.7 and 0.5 atoms/unit charge, respectively. Sputtering rate, H2Se injection rate, and H2Se and H2 partial pressure measurements were consistent with the overall reaction Cu+In+2H2Se→CuInSe2+2H2. The formation of near-stoichiometric coatings appears to be aided at elevated temperatures by a reemission mechanism which removes excess In. Photovoltaic devices formed by evaporating CdS onto the sputtered CuInSe2 yielded short circuit currents of about 33 mA/cm2 and efficiencies of about 4%.

Solid solution, lattice parameter values, and effects of electronegativity in the (Cu1−xAgx)(Ga1−yIny)(Se1−z Tez)2 alloys

Equilibrium conditions for the alloy system (Cu1−xAgx)(Ga1−yIny) (Se1−zTez)2 were determined throughout the complete range of composition. Polycrystalline samples of 125 different compositions, i.e., with x, y, and z=0, 0.25, 0.5, 0.75, and 1.0, were prepared by a melt and anneal technique. Different annealing temperatures in the range 600–800 °C were used depending upon the alloy composition and annealing times of up to 5 months used to attain equilibrium conditions. Debye-Scherrer x-ray powder photographs were used to investigate the equilibrium conditions. It was found that single phase chalcopyrite structure was obtained for all compositions of the copper (x=0), indium ( y=1), and tellurium (z=1) sections but that miscibility gaps occurred in the silver (x=1), gallium ( y=0), and selenium (z=0) sections, and that these miscibility gaps extended through the general alloy system. Values of lattice parameters a and c were determined for all samples showing single phase condition and for each of the above sections the variations of a and c with composition were fitted to power series in the appropriate composition coordinates. Hence contours of constant a and constant c were determined. From the parameters for each section, general series expressions in x, y, and z were developed and the values from these compared with the experimental data for the general alloys. It is shown that a modified Weaire and Noolandi relation of the form [2−(c/a)] =K(XI−XIII+qXVI)2 fits all of the experimental data. Averaged values of K and q were obtained by fitting separately to different sections of the alloy system and also to all alloys of the complete system.

Lattice parameter and optical-energy gap values for (Cu1−x Ag x ) (Ga1−y In y ) (Se1−z Te z )2 Alloys

In the general system (Cu1−x Ag x )(Ga1−y In y )(Se1−z Te z )2, samples were prepared for the six sections defined by the valuesx=0, 1,y=0,1 andz=0,1. The polycrystalline samples were prepared by a melt and anneal technique, different annealing temperatures being used depending upon the alloy composition and annealing times of up to 4 months being required to give equilibrium conditions. Debye-Scherrer X-ray powder photographs were used to investigate the equilibrium conditions and it was established that a single-phase chalcopyrite structure was obtained at most compositions in vestigated. Values of lattice parametersa andc were determined and for each section the variations ofa andc with composition were fitted to power series in the appropriate composition coordinates. Hence contours of constanta and of constantc were determined. Values of optical-energy gapE 0 were determined by opticalabsorption measurements for alloys in the copper (x=0) and indium (y=1) sections. These values were also fitted to power series and contours of constantE 0 determined.

Growth and characterization of CuIn1−x Fe x Te2 compounds

CuIn1−xFexTe2 crystal samples withx varying from 0 to 1 have been grown by a programmed-directional-freezing technique. All compounds withx≤0.3 had a single-phase chalcopyrite structure, whereas secondary-phase formation has been observed forx>0.3. Indications of anomalous behaviour in the electrical and magnetic properties atx≃0.1 could be explained due to the delocalization ofd electrons originating from thep/d mixing and due to the strong covalence of the chalcopyrite compounds.

Some Cross‐Substitutional Alloys of CdTe

The alloys of with the cross‐substitutionally derived ternary compounds and are considered. It is found, in the case of the ternaries themselves, that neither is completely stable and that both tend to decompose under certain conditions of annealing. The alloys have been prepared by melt and anneal method, with due regard to the stability of the ternary concerned. By x‐ray powder photograph techniques, the composition ranges for single phase zinc blende or chalcopyrite structure or for twophase behavior have been determined and the lattice parameter data are given. For the single phase alloys, values of optical energy gap have been determined by the usual I. R. absorption method.