Evidence for Ferroelectricity of All-Inorganic Perovskite CsPbBr₃ Quantum Dots

The combination of ferroelectric-optical properties in halide perovskites has attracted tremendous interess because of its potential for optoelectronic and energy applications. However, very few reports focus on the ferroelectricity of all-inorganic halide perovskites quantum dots. Herein, we report a excellent ferroelectricity in CsPbBr₃ quantum dots (QDs) with a saturation polarization of 0.25 μC/cm². Differential scanning calorimetry, X-ray diffraction, and transmission electronic microscopy revealed that the mechanism of ferroelectric-paraelectric switching of CsPbBr₃ QDs can be attributed to the phase transition from cubic phase (Pm3̅m) to the orthorhombic phase (Pna2₁). In the orthorhombic CsPbBr_3, the distortion of octahedral [PbBr₆]^4- structural units and the off-center Cs⁺ generated the slightly separated centers of positive charge and negative charge, resulting in the ferroelectric properties. The variable-temperature emission spectrum from 328 to 78 K exhibits green luminescence and a gradual red shift due to the phase transition. This finding opens up an avenue to explore the ferroelectric-optical properties of inorganolead halide perovskites for high-performance multifunctional materials.