Enhanced structural stability of formamidinium lead bromide (FAPbBr3) perovskites in confined and coated configurations under varying pressures

Abstract

Formamidinium lead bromide (FAPbBr₃) perovskites are a rapidly emerging class of materials that have the potential to revolutionize optoelectronic and photovoltaic industries. It is now recognized that FAPbBr₃ photoelectronic properties are strongly influenced by the underlying perovskite structure, with static and dynamic disorder among the lattice sites playing prominent roles. We show how these structure–property interactions may be exploited to enhance the photoluminescent properties of FAPbBr₃ by increasing the relative amount of FAPbBr₃ that is exposed to the surface of a substrate material. For example, encapsulating FAPbBr₃ inside the nanopores of a poly(ether ether ketone) (PEEK) membrane or coating it on a yttrium aluminum garnet (YAG) fiber increases photoluminescence stability by a factor of at least 16. FAPbBr₃ in these different configurations is then examined with isothermal, pressure-dependent infrared spectroscopy to better understand the origin of this enhancement. In its bulk form, FAPbBr₃ undergoes two discernible pressure-induced phase transitions at approximately 0.7 and 1.8 GPa, leading to notable red shifts in NH₂ stretching and bending band wavenumbers of the FA⁺ cations. However, confined and coated forms of FAPbBr₃ experience reduced amounts of band shifting across these phase transition pressures. These differences point to some degree of structural stabilization (at least from the perspective of the FA⁺ cations) upon pressurization.