Optical properties of polyelectrolyte quantum dot multilayer films prepared using the layer by layer self-assembly method

Abstract

In this work, we have used spectroscopic ellipsometry to study the optical properties of polyelectrolyte-PbS quantum dot (QD) multilayer films prepared using the layer by layer self-assembly method. The optical results provide information about the absorption coefficients of the materials as a function of the number of layers deposited on a quartz substrate. We have found that the fundamental energy gap of the films decreases linearly upon addition of each layer due to the formation of nanoclusters at the surface. Furthermore, the influence of PbS QD concentration in colloidal dispersion on the energy gap of the materials is examined in detail, and it is found that the optical band gap in the films is in agreement with the linear absorption measurements in the PbS colloidal dispersion from which the film deposition takes place. Finally, the observed electronic transitions of the films corroborate that nanoparticles in the regime of strong quantum confinement are present in the films. This comprehensive fundamental study provides important information, necessary for photovoltaic applications, about the absorption tunability of these nanofilms.