Lattice engineering for enhancing the stability of CsPbI 3 /Cs x FA 1– x PbI 3 quantum dots synthesized via a direct arrangement

The inherent structural instability of red-emitting cesium lead iodide (CsPbI 3 ) 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 CsPbI 3 QDs by coating them with a Cs x FA 1− x PbI 3 (FA = formamidinium, x = 0.25 or 0.75) cluster via a facile direct arrangement synthesis method. The resulting CsPbI 3 /Cs x FA 1− x PbI 3 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 CsPbI 3 , no discernable photoemission peak shift was observed for CsPbI 3 /Cs 0.25 FA 0.75 PbI 3 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 CsPbI 3 /Cs 0.25 FA 0.75 PbI 3 compared to CsPbI 3 in less than 5 min. These resistances to thermal stress and degradation in polar solvents were attributed to the passivation of the CsPbI 3 particles by the pseudo-orthorhombic Cs x FA 1− x PbI 3 cluster. DFT calculations revealed that the addition of FA substantially changes the morphology of CsPbI 3 , but FA itself does not contribute significantly to the electronic transitions within the crystal. Therefore, the Cs x FA 1− x PbI 3 cluster on the surface of CsPbI 3 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 CsPbI 3 QDs by surface modification, which potentially could be used for optoelectronic devices.