Abstract
Cu(In,Ga)Se2 is one the favorite semiconductor for producing thin 2nd generation solar cells. Its bandgap increases with the gallium content, starting from 1,02 eV for CuInSe2 (x = 0) up to 1,67 eV for CuGaSe2 (x = 1). Studies on solar cells efficiency versus gallium content show that the best performance is obtained for a bandgap of 1,2 eV (x = 0,35). Above this gallium content the performances of solar cells decrease invariably. The goal of this thesis is to find out why performances decrease for Cu(In,Ga)Se2 solar cells with high Ga content. First, properties of Cu(In,Ga)Se2 are studied through two growth campaigns of Cu(In,Ga)Se2 with various Ga content by PVD. Absorber properties are studied using different characterization techniques. A modeling of (112) XRD peak developped during this Ph. D. is presented. This analysis, which allows to deduce the group III elements distribution shows that the group III elements diffusion is less efficient within cells containing a high amount of gallium. Jointly with the other characterization techniques, results show that the growth temperature usually used (T < 600°C) seems to be too low for absorbers with high gallium content. This growth temperature is limited to 600°C by the soda lime glass substrate. This substrate is used for its thermal expension coefficient close to the Cu(In,Ga)Se2 one. The natrium content of soda lime glass improves the electrical properties of Cu(In,Ga)Se2 solar cells. The last part is devoted to growth of Cu(In,Ga)Se2 at high temperatures. I have been tested several substrates. Then, high temperature growth campaign has been done on sapphire substrate. Results show that increasing the growth temperature improves the Cu(In,Ga)Se2 cristallinity and its microstructure. Nevertheless, as this substrate doesn’t contains natrium, NaF precursor has been used to introduce it into the Cu(In,Ga)Se2 layer for the last two campaigns. Results show that the presence of natrium during the growth of Cu(In,Ga)Se2 layer affects the copper diffusion into the Cu(In,Ga)Se2 and that this effect is more pronounced into layers with a high gallium content.