Formation, Stability and Crystallization of Two-Dimensional Perovskites and Their Interfaces

Metal halide perovskite solar cells have reached the recent efficiency breakthrough of 26.7%, higher than silicon monocrystalline photovoltaics. Such fantastic result was only possible due to a precise control and engineering of the morphology, interfaces, defects, use of multiple cations in perovskite A-site, as Cs, MA (methylamonnium), FA (formamidinium) and additives to improve crystallization, among others. Dimensionality of perovskite materials can be easily controlled by the choice of the cation in the A site and stoichiometry, providing structures from zero (OD), one (1D), two (2D) and three-dimensions (3D), amplifying the use of these materials in a variety of optoelectronic devices.
In this presentation, we will summarize important results using in situ experiments to probe the formation of 2D perovskite materials with different organic cations and their stabilities. Dynamics of the formation of these structures and interfaces in solution or solid state, their stability under thermal stress and aggregation, were studied by in situ experiments probing the samples with both X-rays and/or visible radiation. For that, we employed time-resolved grazing incidence wide angle X-ray scattering (GIWAXS), high-resolution XRD and PL spectroscopies taken at the Brazilian Synchrotron National Laboratory, Lawrence Berkeley National Laboratory and other facilities. In addition, we will present our recent results on the mapping of the 2D nanostructures by cathodoluminescence coupled to SEM/TEM and the impact of the long carbon chain of the organic cations on thermal stability after long periods of light soaking conditions.