UC Berkeley

This dissertation will introduce a new synthetic method toward near-unity photoluminescence quantum yield CsPbBr3 nanocrystals. The synthesis of high quality CsPbBr3 was achieved through the exploitation of the delicate phase boundaries between the lead bromide phase stabilities. By stochiometrically exploring the complex and rich phase map associated with the lead bromide perovskites, deep suppression of non-radiative recombination of excitons generated upon photexcitation was achieved. In doing so, a critical ratio between bromide and lead in solution is established to reduce non-radiative recombination while maintaining phase purity. This dissertation provides additional evidence that halide vacancies are the primary contributor to non-radiative recombination in sub-stoichiometric synthesis of CsPbBr3 nanocrystals. Furthermore, it is proposed that lead vacancies are responsible for non-radiative recombination in when exceeding stoichiometric ratios. The various phase stabilities responsible for the lead deficient CsPbBr3 phase were identified via UV-VIS signatures. In the process, a new lead bromide magic-sized cluster was identified. Transformations of this magic-sized cluster were investigated. A ligand-mediated transformation from magic-sized cluster to an intermediate species was identified. Consequently, further comprehension of the formation of larger lead bromide perovskites was achieved. Exciton diffusion measurements of 2D arrays of the optically efficient CsPbBr3 suggest high inter-nanocrystal coupling. This was achieved through the investigation of the diffusivity of the charge transfer process as a function of temperature. Non-Arrhenius like behavior proves signatures of exciton delocalization over multiple quantum dots.