Investigating the Role π-Rich Solvents Play in the Growth of Cesium Lead Bromide Nanocrystals

In this report, the role that a high-boiling-point solvent type plays on the nucleation and growth, morphology, and crystal-phase transformation of cesium lead bromide nanocrystals (CsPbBr₃) is studied. The CsPbBr₃ products were compared between a one-pot growth mechanism at room temperature (RT) versus a hot-injection mechanism (HI) control using dibenzyl ether (DBE), diphenyl ether (DPE), dioctyl ether (DOE), or 1-octadecene (ODE). The coordination between these solvents and the PbBr₂ salt precursors resulted in different plumbate [PbSBr _<i>n</i> ]^2-<i>n</i> precursors being formed. The S-to-Pb²⁺ coordination within [PbSBr _<i>n</i> ]^2-<i>n</i> was probed by UV-vis and solvent-phase ²⁰⁷Pb NMR, both of which showed considerable coordination between [PbSBr _<i>n</i> ]^2-<i>n</i> and the π-rich DBE and DPE, whose reactivity affected CsPbBr₃ growth. The effect was more pronounced for CsPbBr₃ prepared via RT, where the morphology was tunable, with π-rich solvents producing thin rod-like CsPbBr₃ with a blue emission, compared to the green-emitting thicker platelets formed via HI. While XRD showed crystalline products for both RT and HI, with orthorhombic and cubic forms, respectively, the RT products had considerable surface defects, as was indicated by lower quantum yields, and to understand this the photoluminescent lifetimes were measured by time-correlated single photon counting.