TMSI–TOP: a dual-function precursor for anion exchange and surface passivation via phosphonium iodide formation in CsPb(Br/I)3 perovskite nanocrystals

Abstract

Perovskite materials are known for their unique crystal structure, which allows for easy anion exchange. Notably, the characteristics of the resulting materials can differ substantially depending on the precursors used for the exchange. In this study, we aimed to synthesize red-emitting perovskite nanocrystals by mixing trimethylsilyl iodide (TMSI) with tri-n-octylphosphine (TOP), and through detailed analysis, we found that the mixture led to the formation of phosphonium salt ([TOPH]⁺I⁻) and trimethylsilanol (TMSOH). Through various analyses, we demonstrated that phosphonium salts act as iodine precursors, effectively enabling the composition exchange from CsPbBr₃ to CsPb(Br/I)₃ nanocrystals. In particular, X-ray photoelectron spectroscopy revealed the presence of TMSOH on the surface of the perovskite nanocrystals. Furthermore, the ability of TMSOH to function as a surface-passivating ligand was verified through comparative analysis with other commonly used precursors. We propose a detailed mechanism for the formation of TMSOH and [TOPH]⁺I⁻ based on ³¹P NMR and ¹H–³¹P NMR spectroscopy. Additionally, the LED devices exhibited excellent performance, with a maximum EQE of 21.69% at 669 nm.