John B. Mooney

Spray pyrolysis and heat treatment of CuInSe2 for photovoltaic applications

Abstract Thin films (about 1 μm) of CuInSe2 were prepared by spray pyrolysis. The component ratios in the spray solutions and the glass substrate temperature were varied in order to produce films of the desired stoichiometry and the importance of this starting ratio is demonstrated. The optimum spray conditions were suggested by thermodynamical calculations using a free energy minimization computer program applied to the Cu-In-Se system. Optical absorption studies of the films verified the existence of the proper compound. Heat treatments of the films were performed in order to produce conductivities and crystal structures for photovoltaic applications and are discussed in detail. In particular for CuInSe2 which gives the sphalerite structure under most spray conditions, a short heat treatment of a film with a starting Cu:In:Se ratio of 1.1:1:4 for 10 min at temperatures of 600, 500 and 400°C is described, which produces the chalcopyrite structure.

Spray pyrolysis of CuInSe2

Abstract 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.

Effect of pH on the production of chalcopyrite CuInSe2 prepared by spray pyrolysis

Thin films (∼1 μm) of CuInSe2 were prepared by spray pyrolysis from solutions with various initial Cu:In:Se ratios and in which 75–90% of the acid was neutralized. The substrate temperature was varied between 225 and 300 °C. The chalcopyrite structure dominated the as‐sprayed films with 90% of the acid neutralized and 300 °C substrate temperature. At 225 °C all films were sphalerite independent of the degree of acid neutralization. Unlike previous studies which only produced the sphalerite structure in films prepared from unneutralized solutions, the present study indicates that the chalcopyrite phase can be produced in as‐sprayed films with a range of initial ratios.

Low resistivity CdS(In) films prepared by spray pyrolysis

Abstract Low resistivity films of CdS doped with indium were prepared by spray pyrolysis. The resistivity was measured as a function of both the cadmium-to-sulfur molar ratio and the amount of hydroxylamine hydrochloride (NH 2 OH·HCl) added to the starting spray solution. The amount of indium was kept constant at 3 mol.%. For a Cd:S ratio of 1:0.9 the resistivity drops by about two orders of magnitude from 3400 to 16Ω cm as the NH 2 OH·HCl:Cd ratio is varied from 0 to 4. For Cd:S ratios of 1:1.2 and 1:1.5 the resistivity increases linearly for the same variation of NH 2 OH·HCl:Cd going from 1.5 to 8 Ω cm and from 0.68 to 6.8 Ω cm respectively. These results are discussed in terms of the Cd:S ratio in these systems.

Charge Transfer Radiography Using Cadmium Sulfide

Electroradiographic methods offer a possible alternative to conventional silver halide x-ray film/screen combinations in terms of lower-cost x-ray radiographs and more rapid development techniques. In charge transfer radiography (CTR), a semiconductor solid material exploits a photoconductive mechanism to transfer a latent electrostatic image onto a dielectric surface. The latent electrostatic image is made visible by xerographic toning. The work reported here used a sintered CdS photoconductive layer to produce large-area image receptors for CTR. Measurements of the currents generated by the incident x-ray flux show that, unlike the case for optical radiation, copper/chlorine dopants do not significantly alter the sample sensitivities. However, the sensitivity of materials thus doped is affected by crystal size and binder material. Remarkably, the sensitivity is not strongly dependent on the thickness of the photoconductor. The charge generation energy is shown to be related to the inverse of the applied electric field for both Se and CdS. An empirical expression is derived from the data that relates the exposure to the surface charge available for transference to the dielectric. Examples of paper radiographs are given, and an exposure characteristic curve for the CdS shows that the sensitivity of the sintered CdS plate is similar to normal x-ray films, but less than that of film/screen combinations.