Lattice engineering for enhancing the stability of CsPbI₃/Cs_xFA_1-xPbI₃ quantum dots synthesized via a direct arrangement

The inherent structural instability of red-emitting cesium lead iodide (CsPbI₃) perovskite quantum dots (QDs) poses a significant hurdle for their integration into commercial optoelectronic devices. In this study, we improved the stability of the cubic CsPbI₃ QDs by coating them with a Cs_xFA_1−xPbI₃ (FA = formamidinium, x = 0.25 or 0.75) cluster via a facile direct arrangement synthesis method. The resulting CsPbI₃/Cs_xFA_1−xPbI₃ exhibited visible luminescence between 600 and 650 nm, a full-width half maximum of 38 nm, and a high photoluminescence quantum yield of 86.66%. Unlike in the case of bare CsPbI₃, no discernable photoemission peak shift was observed for CsPbI₃/Cs_0.25FA_0.75PbI₃ in particular at temperatures of up to 373 K and under UV illumination. Moreover, a more sustained luminescence of up to 25 min in the polar solvent was observed for CsPbI₃/Cs_0.25FA_0.75PbI₃ compared to CsPbI₃ in less than 5 min. These resistances to thermal stress and degradation in polar solvents were attributed to the passivation of the CsPbI₃ particles by the pseudo-orthorhombic Cs_xFA_1−xPbI₃ cluster. DFT calculations revealed that the addition of FA substantially changes the morphology of CsPbI₃, but FA itself does not contribute significantly to the electronic transitions within the crystal. Therefore, the Cs_xFA_1−xPbI₃ cluster on the surface of CsPbI₃ promoted their structural stability without any significant changes in its desired optical properties. These results offer unique optical characteristics while boosting the structural robustness of CsPbI₃ QDs by surface modification, which potentially could be used for optoelectronic devices.