In this work, bismuth oxide nanoparticles were successfully deposited on porous silicon (PSi) in order to enhancethe light absorption and reduce the optical losses. The obtained bismuth oxide (Bi$_2$O$_3$)/PSi samples were characterizedby means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electronmicroscopy (SEM) combined with energy-dispersive spectroscopy (EDS), atomic force microscopy (AFM), photoluminescence(PL), UV–visible absorption and reflection spectroscopy techniques. The XRD studies revealed the formation of themonoclinic $\alpha$-Bi$_2$O$_3$ phase. The XPS analysis demonstrates the formation of highly pure Bi$_2$O$_3$ nanoparticles in accordance with XRD results. The SEM and AFM analyses confirmed that the bismuth oxide nanoparticles are well incorporated and uniformly distributed over the surface of PSi without changes in the arrangement and shape of the pores, resulting in an optimized microstructure. The Bi$_2$O$_3$/PSi films showed better absorption than PSi layers as indicated by UV–Vis absorption technique. The reflection measurements confirmed a further reduction in reflectivity of PSi from 6.4 to 3.5% after the inclusion of Bi$_2$O$_3$ nanoparticles, which is of significant importance for solar cells application since it can enhance its conversion efficiency. The Bi$_2$O$_3$/PSi films have a great promise to be used as efficient antireflection coatings in innovative concepts of higher efficiency and cost-effective solar cells.