Rujun Sun

Reaction Mechanism of Cu(In, Ga)Se2 Formation During Milling Process of Powder Mixture of Cu2Se, In2Se3 and Ga2Se3

Sputtering targets of CIGS quaternary ceramic were fabricated by hot-press sintering the milled powder mixture of Cu2Se, In2Se3 and Ga2Se3. When the milling time of the powders less than 4 h, the sintered targets delaminated, while the delamination disappeared with the prolonging milling time. Therefore the physico-chemical changes of the powder mixture during the milling process and their influence on the delamination of the targets were investigated. The results indicate that with the progress of the milling process, mechanical alloying (MA) occurred, and chalcopyrite Cu(In, Ga)Se2 (CIGS) formed from Cu2Se, In2Se3 and Ga2Se3; With the increasing milling time, CuInSe2 (CIS) formed on the surface of binary copper selenide firstly and CIGS was subsequently generated due to the inward diffusion of Ga; Thus the original blend powders became a mixture of CIGS and residual Ga2Se3 after milling for 48 h. Since CIGS and Cu2-xSe have a similar crystallographic structure, therefore this epitaxial relation may facilitate the formation of CIGS. The disappearance of Cu-Se binary compound and the formation of CIGS restrained the delamination of the CIGS targets in the sintering process.

Influence of Annealing Temperature on Electric Properties of CuIn1-xGaxSe2 Thin Films

The as-deposited CuIn1-xGaxSe2(CIGS) thin films were fabricated by magnetron sputtering from a quaternary CIGS target, and then the as-deposited films were annealed in a temperature range from 240℃ to 550℃. The effect of the annealing temperature on the electric properties(carrier concentration and carrier mobility) of the films was investigated in particular. The results show that when the annealing temperature was lower than 270℃, the highly conducive CuSe phase existed in the films leading to a high carrier concentration(1017-1019cm-3) and a low carrier mobility(~0.1 cm2·V-1·s-1). These films are not suited for CIGS absorber usage. When the annealing temperature was higher than 410℃, the carrier mobility of the films was high about 10 cm2·V-1·s-1and the carrier concentration was in a range of 1014-1017cm-3due to the disappearance of the CuSe phase. When the annealing temperature was higher than 410℃,with the increase of the annealing temperature the grains grew larger and the crystallinity of the films was enhanced, which could reduce the defects in the films and result in the decrease of the carrier concentration. From the aspect of the carrier concentration and the carrier mobility, the appropriate annealing temperature for fabricating the absorbers of the CIGS solar cells is from 450℃ to 550℃.