Calculation of Intraband Absorption Coefficients in Organic/Inorganic Nanocomposites: Effects of Colloidal Quantum Dot Surface Ligand and Dot Size

Hybrid nanocomposite thin films composed of inorganic colloidal quantum dots (CQDs) embedded in an organic conjugated polymer have shown promise as a method for room-temperature infrared detection due to the 3-D confinement of the CQD. The CQDs are coated with a surface ligand material which is comprised of short, organic molecules that prevent the CQDs from aggregating when placed in solution. These surface ligand materials behave as a thin, insulating layer that has been shown to prevent efficient transfer of excited carriers into and out of the CQD. Therefore, it is important to understand the effect that the surface ligand material has on the optical properties of the nanocomposite materials in order to design more efficient hybrid nanocomposite optoelectronic devices. In this paper, we calculate the infrared, intraband absorption coefficient for CQDs in a nanocomposite thin film. The model is verified by comparing the calculated absorption coefficient spectrum to a measured FTIR absorbance spectrum for a specific hybrid nanocomposite material system. Importantly, the CQD surface ligand is included in the model explicitly, which enables the selection of the surface ligand material to be considered as a design parameter for infrared, intraband absorption in hybrid nanocomposites. In addition, the CQD average size is also treated as design parameter in order to tune the infrared, intraband absorption coefficient in hybrid nanocomposites.