Study of ZnO as buffer layer in thin film solar cells based on chalcogenide materials
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Recently, ZnO has taken importance due to its excellent optical, piezo-electric and electrooptical properties, which make it suitable for thin film optoelectronic applications such as blue light emitting devices, short wavelength laser diodes, detectors in the UV-Blue spectral region and buffer layers in photovoltaic devices. A PET / ITO / CdS / PbS / ZnO structure was developed for its application in photovoltaic devices. CdS and PbS thin films were deposited using the chemical bath deposition method The ZnO layer was deposited as a buffer layer using the spin coating technique, three different ways of deposition were investigated un order to compare which of them gave the best properties for the desired application first of them was carried out using a solution of ZnO; secondly, using 30 days aged ZnO nanoparticles and finally 20 minutes aged nanoparticles was applied. A thermal treatment was carried out layer by layer at 150ºC for 30 minutes in a tubular furnance in an ambient atmosphere. The raman spectroscopy analysis in the PET/ITO/CdS/PbS/ZnO TF structure shows dispersion peaks with values in 298 cm-1 and 596 cm-1 corresponding to the 1st and 2nd optical phonons of the CdS, in 143 cm-1 corresponding to the optical phonon (LO) of the PbS and in ~101 cm-1 this is attributed to the E2Low phonon and ~438 cm-1 this attributable to the characteristic phonon in E2High of the ZnO. In the other two structures, the dispersion peaks corresponding to CdS and PbS do not vary from those described above. However, in the structure PET/ITO/CdS/PbS/ZnO Nps aged 30 days it is possible to appreciate the peaks of dispersion corresponding to the ZnO at ~100 cm-1 and 433 cm-1, which are attributed to the phonons E2Low and E2High respectively, in addition two peaks of dispersion are observed.
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