Enhanced structural stability of formamidinium lead bromide (FAPbBr₃) perovskites in confined and coated...

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.