Youn Woo Hong

The changes of morphology and composition in Cu(In1−xGax)Se2 powder synthesis by solvothermal method

To prepare the thin film solar cell by the screen printing method, the synthesis of nano CIGS powder has been frequently studied. Especially, the solvothermal method is normally used in the synthesis of CIGS. However, in the synthesis of CIGS, the experimental studies such as the path of phase formation, the composition change of synthesized CIGS, and the change of powder morphology have rarely been reported. In this study, the changes of phase and morphology of the powders were observed with the ratio of In and Ga ions and the increase of reaction temperature. The phases of CIS and CuIn0.7Ga0.3Se2 were synthesized in a = 0.1. The phase of CIS and two kinds of CIGS coexisted in the range of a = 0.3∼0.7. In a = 0.9, the single phase of CuIn0.9Ga0.1Se2 was synthesized in the same ratio as the source materials. In the case of the a = 0.5 composition, as the concentration of material source and the reaction temperature were increased, the particle size of synthesized CIGS was decreased. The CIGS particles of 200 nm size and the lower aggregate were synthesized in the concentration of 0.01 M at 230 °C.

Molten salt synthesis of La0.8Sr0.2MnO3 powders for SOFC cathode electrode

For La0.8Sr0.2MnO3 (LSM) perovskite, used as the cathode material for solid oxide fuel cells (SOFC), it is known that the formation of a triple-phase-boundary is restrained due to the formation of a second phase at the YSZ/electrode interface at high temperature. To decrease the 2nd phase, lowering the sintering temperature has been used. LSM powder was synthesized by molten salt synthesis method to control its particle size, shape, and agglomeration. We have characterized the phase formation, particle size, shape, and sintering behavior of LSM in the synthesis using the variation of KCl, LiCl, KF and its mixed salts as raw materials. In the case of KCl and KCl-KF salts, the particle size and shape of the LSM was well controlled and synthesized. However, in the case of LiCl and KCl-LiCl salts, LiMnOx as 2nd phase and LSM were synthesized simultaneously. In the case of the mixed salt of KCl-KF, the growth mechanism of the LSM particle was changed from ‘diffusion-controlled’ to ‘reaction-controlled’ according to the amount of mixed salt. The sintering temperature can be decreased below 1000 °C by using the synthesized LSM powder.