Exploration of Optoelectronic Properties in Lead Halide Perovskites

Abstract

Three-dimensional (3D) and two-dimensional (2D) lead halide perovskites have been considered as a promising material for lightemitting diodes and photovoltaics due to its tunable optoelectronic properties such as band gap, absorption or emission wavelength, charge carrier recombination dynamics, etc,. These properties can be finely-tunned to modulate the nanocrystals size, halide ion composition and surface ligands. First, we have investigated Pb-X bonding strength (more ionic Pb-Cl versus more covalent Pb-I) in lead octahedral [PbX6]4- and their impact on growth kinetics in 3D bulk nanocrystals. We determined the activation energies for growth kinetic in CsPbX3 (X = Cl, and I) nanocrystals; 92 kJ/mol for CsPbCl3 and 71 kJ/mol for CsPbI3. Second, we have elucidated the halide ion migration activation energy in 2D lead halide perovskites. Binding mode of spacer ligand in 2D structures generated by multi- or mono- dentate nature of ligand affects the rigidity of lead halide frameworks which is associated with halide vacancy formation and halide stability. Halide ion migration kinetic in RP phase and DJ phase of 2D lead halide perovskites is elucidated by temperature- and thickness- dependent spectroscopic measurements. We determined the activation energies for halide ion migration kinetic in 2D perovskites with different binding mode of spacer; 50.9kJ/mol for Ruddlesden-Popper (RP) vs and 60.8kJ/mol for Dion-Jacobson (DJ) phase, respectively. In summary, understanding such growth mechanism related with chemical bonding of Pb-X and structure characteristic of 2D lead halide perovskites provides strategies for synthesis of dimensionally-tunable perovskites across 3D-2D for optoelectronic application in light-emitting diodes or photovoltaics.