Se–Sb–Ag Optoelectronic Alloy Coatings Prepared by the Green Pulse Electrodeposition Technique in Deep Eutectic Solvents

This study successfully prepared Se–Sb–Ag optoelectronic alloy coatings by pulse electrodeposition in deep eutectic solvents (DESs). The electrochemical behavior of SeO2, SbCl3, and Ag2SO4, in a choline chloride-ethylene glycol DES, was systematically investigated using cyclic voltammetry (CV) and chronoamperometry (CA). CV and CA results revealed an induced codeposition mechanism. The nucleation mechanism of the Se–Sb–Ag alloy coatings between −0.30 V and −0.70 V was identified as a diffusion-controlled three-dimensional (3D) instantaneous process. The effects of pulse potential on surface morphology, composition, crystal structure, and photoelectrical properties of the coatings were systematically examined. The SEM results indicated distinct potential-dependent nanostructural evolution. A moderate negative shift produced smaller secondary nanoparticles and denser, more uniform coatings, whereas an excessive negative potential led to finer but loosely packed nanograins with increased porosity and reduced compactness. The EDS results demonstrated that Ag content initially decreased and then stabilized, Sb content first increased and then declined, while Se content showed an overall increasing trend. The crystalline phases were mainly Ag, Se, Sb, and Ag2Se phases. The coatings exhibited p-type semiconducting behavior. The band gap increased from 0.66 eV to a maximum of 0.76 eV as the electrodeposition potential shifted negatively, followed by a decrease to 0.72 eV at more negative potentials. A similar trend was observed in photocurrent density, which reached a maximum of 0.24 mA/cm2 at −0.80 V. By taking advantage of the strong complexation and solvation capabilities of DESs, this work demonstrates a pulse electrodeposition route suitable for reusing semiconductor elements such as Se and Ag. The electrodeposition mechanism of Se–Sb–Ag ternary coatings was clarified, and pulse deposition in DESs was shown to enable controlled tuning of their structural and photoelectrical properties. These findings indicate that DES-based electrodeposition holds promise for the green preparation of optoelectronic semiconductor materials.