| AVS 57th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Thursday Sessions |
| Session EL+AS+EM+MS+TF-ThA |
| Session: | Spectroscopic Ellipsometry |
| Presenter: | S.G. Choi, National Renewable Energy Laboratory |
| Authors: | S.G. Choi, National Renewable Energy Laboratory O.E. Semonin, University of Colorado J.M. Luther, National Renewable Energy Laboratory M.C. Beard, National Renewable Energy Laboratory A.G. Norman, National Renewable Energy Laboratory Z. Lin, Colorado School of Mines A. Franceschetti, National Renewable Energy Laboratory M.T. Lusk, Colorado School of Mines A.J. Nozik, National Renewable Energy Laboratory |
| Correspondent: | Click to Email |
Discovery of multiple exciton generation from colloidal suspensions of semiconductor quantum dots (QDs) has generated growing interests in realization of high-efficiency QD-based solar cells. Among a number of semiconductor QDs explored up to date, lead chalcogenides such as PbSe and PbS have been of great interest as a result of their wide tuning range of bandgap energy, abundance of materials, and large exciton Bohr radius.
In this presentation, I discuss optical properties of electronically coupled PbSe and PbS QD thin films. A series of QD multilayer thin films were prepared by a layer-by-layer dip-coating method onto glass substrates. Diameter of the QDs varies from 3.2 to 7.2 nm and from 3.5 to 8.3 nm for PbSe and PbS, respectively. Room-temperature pseudo-optical functions of the samples were measured by a rotating compensator-type, variable-angle spectroscopic ellipsometer. Transmittance data were also acquired in a normal-incidence configuration.
First, I determined refractive index N = n + ik of the QD films using the B-spline basis functions within the multilayer model (ambient/surface roughness/QD film/substrate). We use the N obtained as the input parameters for modeling the internal quantum efficiency of the QD-based solar cell devices. Then, I extracted dielectric function ε = ε1 + iε2 for the ensemble of electronically coupled QDs using the Maxwell-Garnett effective medium approximations. The ε spectra show the first exciton peaks, and the E1 and E2 critical-point (CP) structures whose energies are higher than the corresponding bulk values probably due to the quantum confinement effects. This abstract is subject to government rights.