Optical Studies on the Photophysical Properties of Strongly Quantum Confined Lead Bromide Perovskite Nanocrystals
Abstract
Recently, lead halide perovskite (LHP) materials have drawn great research interest in the fields of photonics and photovoltaics as sources of photon and charge carriers thanks to their high defect tolerance and carrier mobility. In contrast to traditional semiconductor materials where the band gap is mostly tuned through size, LHP materials showed tunability in the band gap through continuously variable halide components, which eases the synthesis and device fabrication processes. However, recent advances in the synthetic methods of strongly quantum confined LHP nanocrystals (NCs) have largely expanded the research potential of these materials.
In addition to altering the band gap, imposing strong quantum confinement to LHP materials also modifies their electronic properties as a result of increased interaction of the electron and hole pair and excitons with other degree of freedom due to increased spatial overlap. For instance, strong quantum confinement is known to modify the fine structures of exciton states as a result of increased exchange energy of electron and hole, inverting the relative ordering of the bright and dark exciton states of LHP NCs as compared to their weakly quantum confined counterparts.
In hybrid LHP NCs, the presence of an organic A-site cation, usually methylammonium (MA+) or formamidinium (FA+), introduces in additional degrees of freedom from the rotational and librational motions of the organic cations. In order to explore the role of the organic cations on the exciton transitions, the photoluminescence (PL) spectra and dynamics of strongly quantum confined FAPbBr3 NCs were investigated. These FAPbBr3 NCs showed intense emission from the dark exciton ground state, with significantly shorter dark exciton lifetime in comparison to CsPbBr3 NCs of the same size, suggesting the stronger mixing of bright and dark state.
Moreover, the inter-particle electronic coupling in the arrays of strongly quantum confined CsPbBr3 NCs were investigated by means of PL spectra and dynamics as well. The electronic coupling alters the level structure and relaxation dynamics of bright and dark exciton. The results of electronically coupled CsPbBr3 NCs resembles individual NCs of increased sizes, suggesting delocalization of exciton wavefunction beyond borders of NCs in the electronically coupled arrays.
Citation
Tang, Xueting (2023). Optical Studies on the Photophysical Properties of Strongly Quantum Confined Lead Bromide Perovskite Nanocrystals. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /198972.