Chemical etching of tetrahedrite Cu10Cd2Sb4S13 monograin powder materials for solar cell applications. (February 2022) - Ghisani, Fairouz
Abstract: Cu10 Cd2 Sb4 S13 micro-crystals were synthesized by molten salt method (so-called monograin powder growth) where the synthesis and growth of formed crystals proceeded in the isothermal solid-liquid equilibrium conditions in molten cadmium iodide at 480 °C. During cooling down process the oversaturated part of material dissolved in molten flux at synthesis-growth temperature starts to precipitate onto surfaces of the formed crystals changing the crystals' surfaces unevenly different from the crystals' bulk. To remove selectively the formed precipitates from crystals' surfaces, the tetrahedrite Cu10 Cd2 Sb4 S13 powder crystals were chemically etched with different etchants: Br in methanol (Br2 –MeOH), HCl (concentrated and diluted) and KCN. X-ray diffraction, Raman, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) characterization methods were used in this study. Morphology studies by SEM showed that treatment with diluted HCl and KCN etching, both resulted in smooth crystals' surfaces. Surface analyses by Raman and XPS after etching with diluted HCl and KCN showed that the surface characteristics were almost identical to the features of the bulk of Cu10 Cd2 Sb4 S13 crystals. As detected by SEM, XPS and Raman analyses, the Br2 –MeOH solution reacted aggressively with micro-crystals forming elemental sulfur and oxides on the rough surfaces of crystals. Following KCN and/or HCl treatments removed these formed reaction products. XPS analysis confirmed that the oxidation states of the constituents of the synthesized tetrahedrite compound are as follows: Cu 1+ 10 Cd 2+ 2 Sb 3+ 4 S 2- 13 . Using lasers with wavelength 532 and 633 nm, it was determined for the first time that Raman peaks in the range of 129–132 cm -1 and 167-173 cm -1 belong also to the Cu10 Cd2 Sb4 S13 compound.