Mechanochemical Synthesis of Methylammonium Lead Mixed–Halide Perovskites: Unraveling the Solid-Solution Behavior Using Solid-State NMR

Mixed-halide lead perovskite (MHP) materials are rapidly advancing as next-generation high-efficiency perovskite solar cells due to enhanced stability and bandgap tunability. In this work, we demonstrate the ability to readily and stoichiometrically tune the halide composition in methylammonium-based MHPs using a mechanochemical synthesis approach. Using this solvent-free protocol we are able to prepare domain-free MHP solid solutions with randomly distributed halide ions about the Pb center. Up to seven distinct [PbCl_<i>x</i>Br_6–x]^4– environments are identified, based on the ²⁰⁷Pb NMR chemical shifts, which are also sensitive to the changes in the unit cell dimensions resulting from the substitution of Br by Cl, obeying Vegard’s law. We demonstrate a straightforward and rapid synthetic approach to forming highly tunable stoichiometric MHP solid solutions while avoiding the traditional solution synthesis method by redirecting the thermodynamically driven compositions. Moreover, we illustrate the importance of complementary characterization methods, obtaining atomic-scale structural information from multinuclear, multifield, and multidimensional solid-state magnetic resonance spectroscopy, as well as from quantum chemical calculations and long-range structural details using powder X-ray diffraction. The solvent-free mechanochemical synthesis approach is also compared to traditional solvent synthesis, revealing identical solid-solution behavior; however, the mechanochemical approach offers superior control over the stoichiometry of the final mixed-halide composition, which is essential for device engineering

Composition-Tunable Formamidinium Lead Mixed Halide Perovskites via Solvent-Free Mechanochemical Synthesis: Decoding the Pb Environments Using Solid-State NMR Spectroscopy

Mixed-halide lead perovskites are becoming of paramount interest in the optoelectronic and photovoltaic research fields, offering band gap tunability, improved efficiency, and enhanced stability compared to their single halide counterparts. Formamidinium-based mixed halide perovskites (FA-MHPs) are critical to obtaining optimum solar cell performance. Here, we report a solvent-free mechanochemical synthesis (MCS) method to prepare FA-MHPs, starting with their parent compounds (FAPbX₃; X = Cl, Br, I), achieving compositions not previously accessible through the solvent synthesis (SS) technique. By probing local Pb environments in MCS FA-MHPs using solid-state nuclear magnetic resonance spectroscopy, along with powder X-ray diffraction for long-range crystallinity and reflectance measurements to determine the optical band gap, we show that MCS FA-MHPs form atomic-level solid solutions between Cl/Br and Br/I MHPs. Our results pave the way for advanced methods in atomic-level structural understanding while offering a one-pot synthetic approach to prepare MHPs with superior control of stoichiometry

Fragment-Based Discovery of Type I Inhibitors of Maternal Embryonic Leucine Zipper Kinase

Fragment-based drug design was successfully applied to maternal embryonic leucine zipper kinase (MELK). A low affinity (160 μM) fragment hit was identified, which bound to the hinge region with an atypical binding mode, and this was optimized using structure-based design into a low-nanomolar and cell-penetrant inhibitor, with a good selectivity profile, suitable for use as a chemical probe for elucidation of MELK biology