| AVS 56th International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Aspects of Thin Films Poster Session |
| Presenter: | D.R. Hodges, University of South Florida |
| Authors: | D.R. Hodges, University of South Florida V. Palekis, University of South Florida E. Stefanakos, University of South Florida C.S. Ferekides, University of South Florida |
| Correspondent: | Click to Email |
Cadmium telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal band gap of 1.45 eV, its high optical absorption coefficient and availability of a various device fabrication methods. The status the thin film CdTe solar cell is more than 16.5% efficiency for devices on conducting glass substrates and 7.8% efficiency for devices on flexible metallic substrates. Thin stainless steel (SS) foils are used as the substrate for the development of CdTe solar cells because of its material properties, high temperature stability, commercial availability and cost. A potential problem with the use of a stainless steel foil as the substrate is the diffusion of iron (Fe), chromium (Cr) and other elemental impurities into the layers of the solar cell device structure during high temperature processing. A diffusion barrier limiting the out diffusion of these substrate elements is being investigated in this study. Silicon nitride (Si3N4) films deposited on SS foils are being investigated as the transparent barrier layer, to reduce or inhibit the diffusion of substrate impurities into the solar cell. Si3N4 coefficient of thermal expansion (CTE) of 4.5x10-6/°K is close to both the back contact layer Molybdenum, with a CTE of 5.1x10-6/°K and the absorber CdTe, with a CTE of 5.9x10-6/°K, minimizing thermal expansion mismatch in the device. It has already been shown by others, that substrate impurities like Fe and Cr in the cell’s absorber can lead to reduced cell efficiencies. In this study, the effect of the Si3N4 barrier layer is being evaluated for its effect on cell efficiency and overall device performance. The optimum Si3N4 barrier thickness is also being determined. Currently thin film CdTe cells are being fabricated with and without a Si3N4 barrier layer. Preliminary results show an improvement in the VOC of cells fabricated with a 0.1 µm thick Si3N4 barrier layer. The thin film CdTe solar cells have been characterized by XRD, SEM, Secondary Ion Mass Spectrometry (SIMS) depth profiles, current-voltage (I-V) characteristics and spectral response.