Stabilization of Cubic Crystalline Phase in Organo-metal Halide Perovskite Quantum Dots via Surface Energy Manipulation*

Surface functionalization of nanoscale materials significantly impact their properties due to their large surface-to-volume ratio. We have studied temperature dependent crystal phase transitions in CH₃NH₃PbBr₃ perovskite quantum dots (PQDs) ligated with octylaminebromide (P-OABr) and 3-aminopropyl triethoxysilane (P-APTES), using a framework of static and dynamic spectroscopy. P-OABr undergoes the expected structural phase transition from tetragonal to orthorhombic phase at ~ 140 K, established by the emergence of a higher energy band at 2.64 eV in the photoluminescence (PL) spectrum, while no phase transition was observed in the case of P-APTES. Such phase stabilization is a result of variation in their respective surface energies, an important contributing factor to the Gibbs free energy for nanomaterials. On further investigation, using time-resolved PL, excitation power dependent PL and Raman microscopy over a range of 300 – 20 K, we observe significant differences in recombination rates and charge carrier types between P-APTES and P-OABr. Our findings highlight aspects of PQD phase stabilization linked to nanoscale morphology and surface energy manipulation of the crystal phase diagram.