Page - 175 - in Photovoltaic Materials and Electronic Devices

Coatingsolarcellsorpanelswithnanostructureshasbeenrecentlyinvestigated to enhance the conversion efficiency of the cells [7,8]. In this paper, it is aimed to coat a polycrystalline silicon cell with a thin layer of reduced erbium-doped ceria nanoparticlestoimprovethecellefficiency. Thesynthesizedreducederbium-doped ceria nanoparticles (REDC NPs) would have two main characteristics: to have higher conductivity and to be applicable for optical up- and down-conversions. In detail, the synthesized doped ceria nanoparticles would have relatively high concentrations of tri-valent cerium ions in trap states with a higher concentration of oxygen vacancies. When coated on the solar cells, the synthesized reduced ceria could have higher conductivity and improve the mobility of the generated photoelectrons, due to the increased rate of cerium ion conversion from +4 to +3 states accompanied with an increasing creation rate of charged O-vacancies. In addition, the reduced erbium-doped ceria nanoparticles have the unique material propertiestoactasanopticalmediumforbothdown-conversionandup-conversion at the same time to generate multi-wavelength visible emissions under near-UV and IR excitations, respectively. “Reduced” means that the nanoparticles are synthesized under a reduction environment using hydrogen. This environment helps toformoxygenvacanciesandceriumions(+3states). Theseceriumtri-valent trap states are responsible for optical down-conversion. However, “non-reduced” means that there is no hydrogen during synthesis, which would not form the Ce3+ states. Then, without the reduction environment, the erbium-doped ceria nanoparticles are abbreviated EDC NPs. Then, the used synthesis process results in a high concentration of Ce3+ ions associated with the oxygen vacancies in ceria, which is required to obtain high fluorescence efficiency in the down-conversion process. Simultaneously, the synthesized nanoparticles contain the molecular energy levels of erbium that are required for up-conversion. Therefore, REDC NPs whicharesynthesizedusingthisprocedurecanemitvisible lightwhenexcitedwith either or both UV or IR photons. The synthesized nanoparticles were analyzed using optical absorbance spectroscopy, direct band gap calculations, fluorescence spectroscopy, transmission electron microscope (TEM), X-ray diffraction (XRD) and the electrical conductivity measurement. Then, the synthesized reduced nanoparticles were coated on polycrystalline silicon cells for improving the cell efficiency, which has been proved through I–V analysis, in addition to other cell characteristics such as open circuit voltage, short circuit current, and fill factor. Also, rate generation and E-field distributions of the coated cell were analyzed. Compared to other ceria nanostructure coatings in the literature [9–11], our novel coating offers the simultaneous enhancement of both optical and conductive properties which leads to improving the solar cell's efficiency without considering the traditional anti-reflection coatings. In addition, our synthesized nanoparticles 175