Ana Flavia Nogueira1
University of Campinas1
Owing to their exceptional properties, metal halide perovskites have been incorporated in tandem solar cells. For silicon-perovskite tandem, Br-rich perovskites with a wide-bandgap are required. However, the increase in Br content causes halide distribution heterogeneities and photoinstability. Methylammonium chloride (MACl, MA = CH<sub>3</sub>NH<sub>3</sub><sup>+</sup>) is often added to the perovskite precursor solution to improve optoelectronic properties and performance. However, the effect of MACl additive on Br-rich perovskites is poorly understood.<br/>In this presentation, we will summarize the previous studies from our group where <i>in situ</i> experiments coupled to synchrotron radiation were important to identify intermediates compounds, other metal halide phases during the steps of formation, crystallization and annealing.<br/>In the second part of the talk, we will focus on metal halide perovskites with different amounts of Br and MACl using the N-methyl-2-pyrrolidone (NMP) solvent and the gas quenching deposition method. Simultaneous grazing-incidence wide-angle X-ray scattering (GIWAXS) and photoluminescence spectroscopy (PL) tracked perovskite crystallization and emission properties during the spin-coating and thermal annealing steps. For the perovskites without MACl, the formation of crystalline intermediates depends on the halide proportion. On the other hand, adding the MACl changes the formation mechanism inhibiting the formation of crystalline intermediates. Robust Pb-Cl bond formation decreased the interaction of PbX<sub>6</sub> octahedrons with solvent molecules, preventing the stabilization of intermediate phases containing the solvent. The destabilization of the intermediate phases promoted by the addition of MACl favored the formation of the better crystalline perovskite phase with preferential orientation in the [001] direction and inhibited the photoinduced halide segregation. Nano X-ray fluorescence (nano-XRF) mapping at identified transformations in the elemental distribution, recognizing Br-richer and poorer domains that are reduced for samples prepared with MACl.