Nondestructive Raman Scattering Assessment of Solution-Processed ZnO-Doped Layers for Photovoltaic Applications

This work reports a Raman scattering analysis of doped ZnO layers grown by different solution-based processes (including Al-doped ZnO grown by chemical bath deposition (CBD) and Cl-doped ZnO grown by electrodeposition) that have been developed for the transparent conductive oxide (TCO) window layers in advanced chalcogenide thin film solar cells. The use of different excitation conditions corresponding to resonant and off-resonance measurements is investigated for the Raman scattering assessment of the processed layers. The analysis of the Raman spectra indicates that off-resonance excitation with a wavelength of 442 nm provides the most useful information. The spectra measured under these conditions are characterized by the existence of two distinct spectral regions that are sensitive to electrical and structural characteristics of the layers: (a) the spectral contribution located in the 500 cm –1 region is mainly sensitive to the charge carriers density in the layers, and (b) the relative intensity of the A 1 (LO) peak correlates with the strain measured by XRD on the processed samples. These results confirm the intrinsic origin of the Raman contribution located at the 500 cm –1 spectral region characteristic from doped ZnO layers and corroborate the potential of Raman scattering for the development of optical methodologies suitable for the nondestructive electrical and structural assessment of TCO layers for photovoltaic devices.