Chemical etching of Cu2ZnSn(S,Se)4 monograin powder

Cu₂ZnSn(S, Se)₄ (CZTS, Se) monograin powders were synthesized in the liquid phase of molten KI as flux material from binary compounds in evacuated quartz ampoules. Monograin powders were subjected to various chemical treatments with several etchants (HCl, KCN, NH₄OH and Br in methanol (Br₂-MeOH)) to modify the crystal surface. Polarographic analyses of leaching solutions showed that Sn and Se were removed preferably by HCl etching. Treatment with 10% KCN dissolved mainly Cu, Sn and chalcogen, and ammonia solution removed selectively Cu and chalcogen in an approximate ratio of 1:2. From XPS measurements we found that after etching with 1% Br₂-MeOH the material surfaces were Sn-rich. The prepared monograin powders were used as absorber materials in monograin layer solar cells: ZnO/CdS/CZT(S, Se)/graphite. A combination of chemical treatments before the deposition of CdS led to the best parameters of Cu₂ZnSn(S, Se)₄ monograin layer solar cells. The here achieved efficiencies of solar cells were above 4%.