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

Size tunability of semiconducting quantum dots (QDs) is their most attractive characteristic, which allows modulation of their optical and electronic properties. In the case of organo-metal halide perovskite (OMHP) QDs, surface functionalization is one of the routes that offers a unique way to vary the size in a highly precise manner. In this study we use temperature dependent static and dynamic spectroscopy to investigate the effect of four different surface modification protocols on in CH₃NH₃PbBr₃ OMHP QDs using conductive aromatic ligands. Our results indicate that functionalization methods affect quantum yield (QY) based on how well the different ligands passivate the surface states, while simultaneously altering the contribution of those states to the energy landscape that allows us to arrest the structural phase transition of the QDs from tetragonal/cubic to orthorhombic at low temperatures. Further, these ligands allow charge delocalization around the benzoic positions, which improves inter-particle energy transfer efficiency in QD films based on the conjugation state of the ligands. The synthesis of phase stable and high QY QDs that form conducting films is a significant development that will find use in diverse applications.