Lead-free 3D hybrid perovskites based on an aziridinium cation

Abstract

3D hybrid organic–inorganic halide perovskites attract considerable attention due to their outstanding physical properties and promising applications in photovoltaics and light-emitting diodes. Lead-based hybrid perovskites are currently the most studied and applied materials; however, the very high toxicity of lead creates the demand for less toxic lead-free analogues. This paper describes the synthesis and detailed characterization of new 3D tin-based hybrid perovskites with an aziridinium cation (AzrH)SnX₃ (where AzrH = aziridinium and X = Cl, Br or I). All of the obtained perovskites undergo temperature-induced crystallographic phase transitions at low temperatures. (AzrH)SnBr₃ and (AzrH)SnI₃ are cubic at room temperature, while upon cooling, they transit into an orthorhombic phase. (AzrH)SnCl₃ is orthorhombic at room temperature and reduces its symmetry to two different monoclinic phases upon two consequent transitions. Crystallographic experiments allowed us to obtain ordered structures of the aziridinium cation for the first time. UV-vis measurements showed that (AzrH)SnX₃ perovskites exhibit absorption edges, characteristic of semiconducting materials. The optical band gaps of the obtained compounds were found to be 3.48 eV (Cl), 2.46 eV (Br) and 1.54 eV (I) according to Tauc plots. Thus, the discovered compounds form a new group of 3D semiconducting lead-free perovskites that can widen the range of suitable materials for the production of solar cells and light-emitting diodes.