Enriched Photophysical Properties and Thermal Stability of Tin(II) Substituted Lead-Based Perovskite Nanocrystals with Mixed Organic–Inorganic Cations

In order to overcome the toxicity and long-term stability of hybrid organic/inorganic Pb-based halide perovskites, which are believed to be the key obstacles for their utilization in optoelectronic devices, herein we explored the synthesis of binary Pb–Sn perovskite nanocrystals (NCs) with fixed composition of methylammonium (MA) and cesium (Cs) cations. Mixed MA-Cs composition has been used to achieve an improvement in thermal stability and photophysical property of binary Pb–Sn systems. However, challenges lie in how to accomplish much better or identical optical properties and thermal stability of complex mixed cationic Sn-substituted systems when compared to pristine Pb-based perovskites by maintaining the divalent state of Sn under ambient condition. With the intention of circumventing the oxidation of Sn²⁺, we synthesized for the first time a series of perovskite NCs, MA₀.₅Cs₀.₅Pb₁–ₓSnₓBr₃ (i.e., 0 ≤ x ≥ 0.5) using room-temperature ligand-assisted reprecipitation (LARP) method without maintaining inert atmosphere. A substantial advancement toward higher relative photoluminescence (PL) quantum yield, prolonged charge carrier lifetime, and enhanced environmental and thermal stabilities was achieved at a fixed composition through alloying with Sn (i.e., MA₀.₅Cs₀.₅Pb₁–ₓSnₓBr₃ NCs, at x = 0.3). Interestingly, Raman spectroscopic analysis along with powder X-ray diffraction patterns and microscopic images suggest that the Sn substitution did not affect the crystal structure and the chemical interplay between the organic cation and inorganic framework of pristine MA₀.₅Cs₀.₅PbBr₃ NCs. Such understandings are constructive en route for improving the properties of Sn-substituted Pb-based perovskite NCs with reduced toxicity for their execution in forthcoming optoelectronic technologies.