Halogen in materials design: Fluoroammonium lead triiodide (FNH3PbI3) perovskite as a newly discovered dynamical bandgap semiconductor in 3D

Abstract

AbstractMethylammonium lead triiodide (CH3NH3PbI3) has been recognized as one of the record‐breaking materials for photovoltaics since it can potentially convert light energy into electricity @ 23%. However, it has been suffering from serious stability and environmental issues for which it is not yet put on market. To this end, experimental and theoretical studies are underway to discover versatile halide‐based perovskite compounds. In this article, we report the polymorphic geometries, stabilities, band structures, density of states spectra, and carrier effective asses of a newly identified perovskite semiconductor called fluoroammonium lead triiodide (FNH3PbI3), obtained using compositional engineering combined with periodic density functional theory electronic structure calculations. We show that this compound is stable both in the orthorhombic and pseudocubic phases. We also show that the bandgap for this material oscillates between 1.62 eV (direct) and 1.79 (indirect) for the two polymorphs examined in the pseudocubic phase, with the former and latter values corresponding to the [111] and [110] orientations of the inorganic cation inside the perovskite cage, respectively. Contrariwise, it is direct at Γ‐point for the polymorph examined in the orthorhombic phase. The spin orbit coupling is displayed to have profound effect on the nature and magnitude of the bandgap for this material. This, together with the very small effective masses calculated for the charge carriers comparable with those of CH3NH3PbI3, allows us to propose that FNH3PbI3 could be a possible candidate for photovoltaics, as well as for other optoelectronic applications.