Abstract
This work reports a detailed resonant Raman scattering analysis of ZnMgO solid solution nanometric layers that are being developed for high efficiency chalcogenide solar cells. This includes layers with thicknesses below 100 nm and compositions corresponding to Zn/(Zn + Mg) content rations in the range between 0% and 30%. The vibrational characterization of the layers grown with different compositions and thicknesses has allowed deepening in the knowledge of the sensitivity of the different Raman spectral features on the characteristics of the layers, corroborating the viability of resonant Raman scattering based techniques for their non-destructive quantitative assessment. This has included a deeper analysis of different experimental approaches for the quantitative assessment of the layer thickness, based on (a) the analysis of the intensity of the ZnMgO main Raman peak; (b) the evaluation of the changes of the intensity of the main Raman peak from the subjacent layer located below the ZnMgO one; and (c) the study of the changes in the relative intensity of the first to second/third order ZnMgO peaks. In all these cases, the implications related to the presence of quantum confinement effects in the nanocrystalline layers grown with different thicknesses have been discussed and evaluated.
Highlights
Thin film photovoltaics have made important progress in the recent years and have recently surpassed the efficiency of multicrystalline wafer-based devices[1]
The obtained results corroborate the viability of resonant Raman scattering based techniques for the non-destructive quantitative assessment of the layers with thickness and compositions corresponding to those required for the development of high efficiency chalcogenide solar cells
The study of layers that were grown with different thicknesses has allowed to analyse the viability of different experimental approaches for the non-destructive quantitative assessment of the thickness of the layer, including: (a) the analysis of the intensity of the ZnMgO main Raman peak; (b) the evaluation of the changes of the intensity of the main Raman peak from the subjacent layer located below the ZnMgO layer; and (c) the study of changes in the relative intensity of the first to second/third order ZnMgO peaks
Summary
Thin film photovoltaics have made important progress in the recent years and have recently surpassed the efficiency of multicrystalline wafer-based devices[1]. It is clear that a fast (with measuring times below 1 minute) and non-destructive methodology capable of probing thickness and composition in-line is a very valuable tool for the potential transfer of these technologies to industrial production processes For these applications, optical spectroscopy based on Raman scattering has already proved its versatility for controlling various important material parameters of the stacks used in thin film solar cells, including crystallinity[8], absorber and buffer composition[9, 10], buffer layer thickness[8], presence of secondary interfacial phases[11, 12] and doping concentration[13] in separate layers, as well as complete devices[8]. The range of compositions is confined within the Zn-rich region with 0 < Mg/(Mg + Zn) < 0.3321, 22, where the ZnMgO solid solution has a wurtzite structure
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