Influence of Solution Acidity on the Growth, Structural and Optical Properties of Co-electrodeposited Cu2SnS3 thin Films: Experimental and DFT Discussions

The present study investigates how the acidity of the medium influences the nucleation of Cu-Sn-S elements to develop co-electrodeposited Cu2SnS3 films suitable for solar cells. The effect of solution acidity on CTS film properties was investigated by varying the pH from 1.4 to 4.4, using tartrate as a stabilizing agent for Cu and Sn through complexation. After co-deposition at a selected potential of - 0.95 (vs. SCE), and after a sulfurization step at 400 degrees C, the obtained results have clearly demonstrated the effect of acidity on the development of CTS films and, consequently on their physico-chemical properties. More specifically, X-ray diffraction and Raman spectroscopy confirmed this effect of pH, since a Cu2SnS3 phase was progressively formed as the pH increased, to crystallize at the end in a triclinic structure at pH = 4.4. EDS analysis and calculated structural parameters showed a higher pH significantly increased the crystallinity and minimized the formation of secondary phases. Similarly, SEM mapping analysis revealed a very uniform grain distribution with an optimal Cu/Sn ratio stoichiometry of similar to 1.99, particularly at pH = 4.4, along with a slight copper deficiency favoring p-type conductivity. Furthermore, the experimentally found optical bandgap decreased from 1.34 eV at pH = 1.4 to 1.25 eV at pH = 4.4. Finally, to highlight these results, a simulative calculation was conducted within the framework of density functional theory (DFT). The comparison of experimental and theoretical results showed good agreement, with confirmation of the semi-conductive character of the CTS material, as well as its direct bandgap of the same order of magnitude 1.15 and 1.29 eV. [GRAPHICS] .