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

Abstract

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 (FAPbX; 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.

Cu(II)-Doped Cs2SbAgCl6 Double Perovskite: A Lead-Free, Low-Bandgap Material

“…38 Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical tool that allows one to characterize atomic-level short-and medium-range structure, as well as dynamics in hybrid perovskites. 15,[57][58][59][60][61][62][63][64][65][66][67][68][69][70][71] NMR spectroscopy was used to decode the local atomic structure of the Cs2SbAgCl6 parent and Cu 2+ -doped Cs2SbAgCl6 double perovskite materials. In addition to NMR spectroscopy, powder X-ray diffraction (PXRD) was used to confirm the crystalline structure and phase purity, while optical properties were obtained using diffuse reflectance (DR).…”

Making by Grinding: Mechanochemistry Boosts the Development of Halide Perovskites and Other Multinary Metal Halides

“…This simple method was first demonstrated in 2013 by Stoumpos et al who synthesized different hybrid organic–inorganic iodide perovskites in this way . The same hand grinding approach was later employed by several other groups to prepare similar LHPs . While this is probably the simplest possible approach, hand grinding can be tedious and most importantly may lead to unreacted precursor impurities in the sample.…”

Mechanosynthesis, Optical, and Morphological Properties of MA, FA, Cs‐SnX3 (X = I, Br) and Phase‐Pure Mixed‐Halide MASnIxBr3–x Perovskites

“…In general, preparation methods of perovskites require energy‐consuming solvothermal conditions using elevated temperatures and pressures for homogeneity of reaction mixtures . Recently, a broad set of alternative synthesis methods of metal halide perovskites involving ultrasound‐assisted,, microwave‐assisted, and mechanochemical approaches has been developed. Among them, the mechanochemical reactions offer a significant advance by avoiding the use of solvent, dramatically shortening synthesis times and providing phase‐pure products.…”

“…More recently, Kanatzidis and co‐workers utilized the solid‐state grinding method for the synthesis of 2D layered Ruddlesden–Popper (BA) 2 (MA) n ‐1 Pb n I 3n+1 ‐type perovskites . A number of the resulting mechanoperovskites appeared as convenient materials for high‐sensitivity solid‐state NMR studies to directly probe the atomic‐level phase composition of mixed‐cation and mixed‐halide perovskites and for thin films formation using vacuum deposition method . Moreover, while conventional solution‐processing for Cs‐based perovskite synthesis is rather challenging due to the poor solubility of cesium halides in common organic solvents, the mechanochemical approach provided an efficient one‐step general method for incorporating poorly soluble salts into multi‐component perovskite crystal lattices.…”