Applications of spectroscopic ellipsometry for multilayer analysis of CdTe solar cell structures incorporating Magnesium–Zinc oxide high resistivity transparent layers

Abstract

An optical function parameterization of polycrystalline MgxZn1-xO (MZO) thin films as a function of bandgap Eg has been utilized in applications for the metrology of CdTe-based solar cell structures that incorporate MZO thin films as high resistivity transparent (HRT) layers. Parametric expressions are applied to facilitate mapping spectroscopic ellipsometry (M-SE) of device structures consisting of glass/SnO2:F/MZO. M-SE is shown to provide maps in the MZO effective thickness and bandgap within confidence limits of ± 1 nm and ± 0.003 eV, respectively. As a second application of these parametric expressions, an as-deposited glass/SnO2:F/MZO/CdS/CdTe device structure has been analyzed by through-the-glass spectroscopic ellipsometry (TG-SE). Such an analysis is also shown to provide the MZO effective thickness and bandgap. The outcome of the TG-SE analysis for this device structure enables simulations of the external quantum efficiency (EQE) spectrum of the resulting solar cell assuming different recombination losses within the individual layers of the structure. A comparison of these simulations with the experimental EQE spectrum reveals improved current collection from the front of the device incorporating an MZO HRT layer.