M. Kauk

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.

CZTS Monograin Powders and Thin Films

This paper reviews results of studies on different materials and technologies for polycrystalline solar cells conducted at Tallinn University of Technology. Structural properties and defect structure of kesterite CZTS compounds (Cu2ZnSnSe4, Cu2ZnSn(SSe)4) were studied. Influence of selenization parameters of a Zn-Cu-Sn stacked layer on the CZTS layer growth and on the morphology, distribution of elements was analyzed. All the results obtained have been used to optimize the technology of producing solar cell structures in different designs. Cu2ZnSnSe4 and, Cu2ZnSn(SSe)4 based monograin layer solar cells were developed.

ZnO grown by chemical solution deposition

Zinc oxide (ZnO) films were grown on different substrates by the chemical solution deposition method from an ammonium zincate complex solution. The structure, morphology, composition, and optical properties of the films were studied by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV-VIS spectroscopy. Results reveal that the deposited layers consist of ZnO nanorods with strong c-axis orientation. The observed Raman spectra are in excellent agreement with those reported in literature. The E2(high) mode at 437 cm−1, having the strongest intensity of all samples, is characteristic of the ZnO hexagonal wurzite structure. The diameter of the rods is about 90 nm and the thickness of the ZnO layer is between 140 nm to 2,3 µm. Different deposition parameters such as the concentration of the zincate complex and the temperature of the bath, the deposition time and dipping process effects are discussed.

Growth of CuInSe 2 monograin powders with different compositions

CuInSe 2 monograin powders (MGP) were synthesized from Cu-In alloys of different Cu/In concentration ratios and elemental Se in liquid phase of flux material in evacuated quartz ampoules. The surface morphology, phase structure, and composition of the powder crystals were analyzed by scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray analysis respectively. Bulk composition was analyzed polarographically. Photoluminescence spectra were measured at 9 K. It was found that the composition of MGP material (Cu/In concentration ratio) can be controlled by the concentration ratio of precursor Cu-In alloys. Single phase CuInSe 2 growth is realisable between 0.7 2 . Samples with high In content exhibited two broad bands with peak positions at 0.86 and 0.93 eV.

Tailoring the composition and properties of CuInSe2 materials for solar cell application

Ternary semiconductor compound CuInSe2 is one of the most promising absorber material used in solar cells. In this study, we used CuInSe2 powder materials synthesized in molten salts. Modifying the preparation conditions, we studied the relationships between the initial and final composition, and determined the preparation conditions for the single- phase growth of CuInSe2. The as-grown samples were annealed in selenium or sulfur vapor at various temperatures for a different time period to change the CuInSe2 material properties. Se vapor treatment has been found to influence the bulk composition. Sulfur vapor treatment has been found to improve the open-circuit voltage of the completed cells by about 100 mV. It could be attributed to an increase of the band gap at the surface of the absorber due to the formation of a wider band gap CuIn(S,Se)2 material. The incorporation of sulfur into CuInSe2 reduces the carrier recombination in the interface region, which was indicated as an improvement of the fill factor of the cells.