Co-electrodeposition of Cu₃BiS₃ thin films in weakly alkaline aqueous solutions for photovoltaic application

The semiconductor copper bismuth sulphide (Cu₃BiS₃) has been perceived as a promising photovoltaic (PV) absorber material thanks to its proper bandgap, high absorption coefficient and nontoxic component elements. However, the lack of high-quality absorber layers with satisfactory performance hinders its development in PV filed. Herein, we developed a novel co-electrodeposition process to fabricate Cu₃BiS₃ thin films in weakly alkaline aqueous solution. The electrodeposition mechanism and the electrochemical behavior of ions were investigated in detail by cyclic voltammetry (CV) tests. Scanning electron microscope showed the transformation of Cu₃BiS₃ precursors in microstructure and morphology with the adjustment of the Cu²⁺ ion concentration in the electrolyte. We finally achieved Cu₃BiS₃ thin films with high crystallinity and desirable stoichiometric ratios. By changing the Cu/Bi content, the bandgaps can be tuned from 1.33 to 1.52 eV. Photoluminescence (PL) spectra revealed two kinds of defects related to radiation recombination in the Cu₃BiS₃ film.