WS_2 Monolayer Integration in a FAPbI_3-based Heterostructure

Incorporating a monolayer of WS_2 via interface engineering enhances the overall physical properties of a FAPbI3 perovskite based heterostructure. FAPbI_3/WS_2/TiO_2/ITO and FAPbI_3/TiO_2/ITO heterostructures were analyzed by UV-Vis spectroscopy, X-ray diffraction, scanning electron microscopy and atomic force microscopy. The configuration with WS_2 interlayer presents higher absorption in the visible region with a bandgap of 1.44 eV. WS_2 also enhances the deposition process of FAPbI_3, resulting in the formation of pure photoactive α-phase without the non-photoactive δ-phase nor residual plumbates. The incorporation of the monolayer improves the crystalline structure of the FAPbI_3, promoting a preferential growth in the [100] direction. The smooth surface of WS_2 favors a homogeneous morphology and an increase of the grain size to  4.5 μm, the largest reported for similar structures. Furthermore, the work function obtained lets us propose an enhance an adequate energy band alignment between FAPbI_3 and the n-type layers for the electron flux to the cathode. These findings strongly suggest that the interfacial coupling of FAPbI_3/WS_2 could be a promising candidate in photovoltaic applications.