Surface Chemistry of Lead and Lead Free Metal Halide Nanocrystals

In this thesis, the surface chemistry of different metal halide NCs were investigated. Two new synthesis approaches to produce LHP NCs were developed by employing phosphonic acids (either alkyl or oleyl PAs) as the sole surfactants. The NMR analysis of these samples indicated the steric binding state of PA. PA-capped NCs show near unity PLQY with uncommon truncated shape, and high stability against dilution. We also investigated the interaction between neutral ligands and LHP NCs. Among various neutral ligands, it was found out that oleyl PAs are able to strip a large fraction of original surface species. Surprisingly, after such loss of ligands, the PLQY, morphology and phase of CsPbBr3 NCs remain unaltered, empirically confirming the defect tolerance of LHP NCs. We also studied the surface chemistry of Pb-free double perovskite NCs. We optimized the optical properties of Bi-doped Cs2(NaxAg1-x)InCl6 NCs by systematically varying the amine and acid. We found out that both ligands are anchored to the surface of the NCs. Moreover, we observed that even with a high ligands density, the PLQY of the NCs was still low indicating that ‘normal’ surface passivation is not enough to efficiently passivate these NCs, which suggest that such DP NCs is sensitivity to non-radiative surface traps. We also investigated the optical physical behavior of Sb3+ centers in different coordination environment. The Rb7Sb3Cl16 NCs were composed by isolated [SbCl6]3- octahedra and [Sb2Cl10]4- dimer. The isolated [SbCl6]3- octahedra show dual emission under different excitation, whereas the [Sb2Cl10]4- dimer is non-emissive even in cryogenic temperature. In the final part, we have investigated a special LHP species, so called nanoclusters (NCLs), which was regard as intermediate between molecular precursors and solid LHP NCs. We here firstly revealed their shape and structure by SXAX, WAXS and PDF analysis.