Electrical Behavior and Photocatalytic Activity of Ag-Doped In₂S₃ Thin Films

Indium sulfide thin films with different amounts of silver doping were deposited by spray pyrolysis. The samples were tested as potential photocatalysts by degrading methylene blue (MB) dye aqueous solution under the effect of light. Samples were prepared using precursors with Ag/In ratios of 0 at.%, 4 at.%, and 6 at.%, corresponding to a measured and normalized Ag concentration in the films of 0.0 at.%, 1.4 at.%, and 2.3 at.%, respectively. Scanning electron microscopy revealed that the surface of the films was homogeneous and compact. Within the energy resolution of dispersive x-ray spectroscopy, the films were revealed to be stoichiometric with an S/In ratio of 1.50 ± 0.05. The films exhibited semiconductor behavior, and the best direct-current (DC) conductance was achieved for the film with 1.4 at.% Ag doping. Changes in the Ag concentration led to the activation of different conduction mechanisms, from correlated barrier hopping (for the undoped and for 1.4 at.% Ag-doped film) to overlapping large-polaron tunneling (for the 2.3 at.% Ag-doped film). After immersing the samples in MB solution and exposing them to visible light for 270 min, a significant decrease of the MB absorption was observed. The lowest absorption (and thus highest photodegradation efficiency) was measured for the solution containing the sample with 1.4 at.% Ag doping, showing a photodegradation efficiency of 83%. Considering their performance and relatively low manufacturing cost, such In₂S₃:Ag films could contribute to the solution of environmental problems related to wastewater via photodegradation of contaminants under illumination by sunlight.