Understanding Local Structure in Halide Perovskites: Linking Theory and Experiment

Positional polymorphism in solids refers to the presence of local atomic disorder that is not discernible in standard diffraction experiments. Although positional polymorphism is crucial for understanding the electronic structure of halide perovskites, it is frequently overlooked when interpreting their intriguing properties. In this talk, I will present our recently developed methodology for first-principles calculations of transport and optoelectronic properties of perovskites, based on the special displacement method [1,2]. Our framework allows for the unified and efficient treatment of anharmonic lattice dynamics, electron-phonon coupling, and positional polymorphism. I will connect theoretical findings and experimental results [3,4,5,6,7], beginning with pair distribution functions and expanding to temperature-dependent band gaps, free energies, phonons, effective masses, mobilities, and ultrafast spectroscopy. I will also discuss the role of molecular orientation and size in the degree of polymorphism in hybrid compounds, and make contact with the concepts of the lone pair formation and polarons. Our work opens the way for addressing pending questions on perovskites’ technological applications.