Abstract:
One of the proposed solutions for reducing the cost of electricity produced by the photovoltaic is to reduce the amount of incoming semiconductor materials in the manufacture of solar cells. The thin films solar cells come in response to this requirement. Both ternary CuInX2 (X = Se, Te) and the quaternary Cu(In,Al) Se2, under their chalcopyrites structures, are highly recommended for the fabrication of this solar cells type. The synthesis of these materials using electrodeposition method and their characterizations were the overall goal of this thesis.
All films were deposited onto ITO substrates from aqueous electrolytes. The starting solutions were obtained by the dissolution of copper chloride CuCl2, indium chloride InCl3, aluminum chloride AlCl3, selenium dioxide SeO2 and tellerium dioxide TeO2 in de-ionized water. The as deposited films were annealed under vacuum.
In the first part of this work, we investigated the effect of deposition time on the properties of CuInSe2 and CuInTe2 thin films. Effects of the annealing temperature and the aluminum to indium molar ratio on the properties of the quaternary Cu(In,Al)Se2 have been also studied in the second part.
The XRD investigation proved that, the elaborated films exhibits the CuInSe2 and the CuInTe2 chalcopyrite structure with the high degree of preferred orientation along [112] direction. The chalcopyrite structure was also confirmed from Raman spectroscopy.
In CuInSe2, the peak intensity of the secondary phase In2Se3 decrease with deposition time and it disappeared for the film deposited at 20 min indicating that the formation mechanism of CuInSe2 depend on the binary In2Se3 phase.
For the second ternary, the films deposited at 15 and 20 min exhibits the CuInTe2 chalcopyrite structure as the major phase with In4Te3 as additional binary compounds. Excluding the film deposited at 10 min, the films conductivity is n type and it is controlled by the variation in the carrier mobility rather than by their density.
The elaborated films show the direct allowed band gap and their energy band gap varied within 1.17 to 1.04 eV for CuInSe2 and from 1.06-0.99 eV for CuInTe2.
For the quaternary, polycrystalline Cu(In,Al)Se2 thin films crystallize in the chalcopyrite structure with the preferential orientation in the (112) plane were obtained. The films show the direct allowed band gap, and the band gap energy increased from 1.59 to 1.78 eV with annealing temperature.
The results derived from this work suggest that the elaborated CuInSe2 and CuInTe2 can be used as absorber layer in thin films solar cells and the Cu(In,Al)Se2 as a top absorber layer in tandem solar cells.
