Researchers from the University of Strathclyde and the Belarusian State University have made significant strides in understanding the optical properties of perovskite nanocrystals (PNCs), which are tiny, highly efficient materials with potential applications in the energy sector, particularly in solar cells and quantum photonic devices. The team, led by Jehyeok Ryu and Alexey Y. Nikitin, has developed a method to accurately determine the size-dependent dielectric permittivity of cesium lead bromide (CsPbBr3) PNCs, a crucial factor in designing and optimizing these materials for practical use.
The researchers’ work, published in the journal Nanoscale, addresses a key challenge in the field: obtaining precise measurements of the intrinsic optical properties of individual PNCs. Currently, most studies provide average values from ensembles of nanocrystals, which can obscure important size-dependent variations. To overcome this limitation, the team developed a methodology to reconstruct the size-dependent complex dielectric permittivity of PNCs from the measured absorbance spectrum of a colloidal solution.
The researchers modeled the permittivity of PNCs as a sum of Voigt profile oscillators, with size-dependent transition energies governed by the exciton effective mass. Using a transmission electron microscopy-derived size distribution of the PNCs, they obtained the solution permittivity via the Maxwell Garnett effective medium approximation. This permittivity was then used in a transfer matrix method to simulate and fit the absorbance spectrum, allowing the team to reconstruct the permittivity of the individual PNCs.
The extracted spectral linewidth from the imaginary part of the permittivity was found to be consistent with single nanocrystal emission linewidths at room temperature. Furthermore, finite element simulations demonstrated enhanced absorption cross-section of a single PNC coupled to a nanoantenna, showcasing the applicability of the extracted permittivity in practical devices.
This research provides a valuable tool for the energy industry, particularly in the development of next-generation solar cells and quantum photonic devices. By accurately determining the optical properties of PNCs, researchers can better design and optimize these materials for use in energy harvesting and conversion technologies. Moreover, the methodology developed by the team can be applied to other nanocrystal systems, further expanding its potential impact on the field.
This article is based on research available at arXiv.