Precise Control of Halogen Distribution in Monolayer Hybrid Perovskites through Mechanochemistry

Mixed-halide three-dimensional perovskites have been extensively studied due to their ability to exhibit continuously tunable emissions in the visible spectrum accompanied by spectral broadening. However, understanding the relationship between the spectral characteristics of mixed-halide perovskites and the distribution of halogens at the individual octahedral levels remains a significant challenge. This study successfully realized single-layer mixed-halide perovskites (A₂PbI₂Cl₂) (A = C₁₂H₂₅NH₃⁺) with a uniform distribution of halogens in the Pb octahedra by employing mechanochemical strategies. The absorption spectra of the prepared samples exhibited a constant absorption peak at 476 nm under different balling times, indicating formation of a uniform product. Structural characterization is further elucidated by X-ray photoelectron spectroscopy measurements and corroborated by X-ray diffraction results. Similarly, single-layer mixed-halides A₂PbI₂Br₂ and A₂PbI₂SCN₂, exhibiting constantly absorption peak of 450 and 523 nm, respectively, during the reaction, were obtained by employment of different halogens via this synthetic technique. The versatility of the synthetic strategy was further demonstrated by synthesizing mixed-halide A₂′PbI₂Cl₂ perovskites by substituting a primary amine salt with a quaternary ammonium salt (A′ = C₁₅H₃₄N⁺). Ultimately, these mixed halides exhibit tunable emission spectra ranging from 340 to 530 nm by varying both amine and halogen composition/distribution within the Pb octahedral. This atomic-scale insight lays the foundation for further investigations of the optoelectronic properties of mixed-halide perovskites.