Crystal Structures and Photoluminescence of a Two-Dimensional Perovskite

Arguably the biggest challenge of the high-efficiency perovskite solar cells, such as CH₃NH₃PbI₃ and CH(NH₂)₂PbI₃, is their device instability. A recent study of 2D perovskite compounds, butylammonium methylammonium lead iodide perovskite, [CH₃(CH₂)₃NH₃]₂(CH₃NH₃)_n-1Pb_nI_3n+1, proposed a solution to this problem. This class of materials shows a maximum photovoltaic efficiency of 12.52%, without any obvious degradation over thousands of hours under standard light illumination and humidity test. This talk focuses on the study of temperature-dependent crystal structures, along with the photovoltaic properties of the 2D 1-layer (n = 1) perovskite material. We have performed elastic and inelastic neutron scattering, Raman scattering, and photoluminescence measurements on a powder sample of the 1-layer system ([CH₃(CH₂)₃NH₃]₂PbI₄). Our analysis of the data illuminates the evolution of the lattice structure, rotational and vibrational dynamics with temperature, and their connection to the charge carrier lifetime of the solar cell will be discussed.