Yeni Eu3+ ve Tb3+ Katkılı Fotovoltaik Hücrelerin Tasarımı ve Elektronik Özellikleri Üzerine Teorik Bir Çalışma
Özet
Emissions of lanthanide cations (Ln3+) are very interesting, with narrow and element-specific wavelengths unaffected by the environment, where unauthorized f-f transitions can be observed. These intrusions have low absorbance and long luminescence lifetimes. Europium (Eu3+) and Terbium (Tb3+) ion luminescence is enhanced by complex formation in the aqueous phase or by doping into a solid or hard matrix, both yielding sharp and intense emission bands that are typically long lasting. The glass matrix consists of SiO2 and other inorganic oxides; The addition of B2O3 and ZnO changes the matrix, changing the physical and chemical properties of the glass. Luminescent glasses are attracting increasing commercial interest as colored glasses. Metal oxides dissolved in glasses absorb radiation in certain wavelength ranges specific to the oxides used. Eu3+ and Tb3+ were chosen because they can give long-term radiation. Electrons (-) and holes (+) are formed by UV radiation on glass, which is a solid matrix. In glass consisting of a mixture of SiO2, B2O3 and ZnO, these photo-induced electrons and holes are stably held in the electronic region of the glass, and then Europium or Terbium radiates in the recombination process between these electrons (-) and holes (+). In addition, the glow mechanism of lanthanide ion doped oxide glass is unknown. In this thesis, we first explained this mechanism with the electronic transitions and boundary orbital approach.
Theoretical chemical calculations of lanthanide elements are quite difficult as they contain f orbitals, and the computational basis sets about them are quite limited and are newly developed. In this study, two different computational basis sets developed in recent years for Europium and Terbium were selected, and the Stuttgart basis set was modified as a result of the trials. In the basis set selection, optimizations of (1-10) water coordinated lanthanide complexes were made, and complex structures which stable 8- or 9- coordinates were found for Eu3+ and Tb3+. After the stable complex structure was found, the emission spectra were calculated with the TD-DFT method and the experimental results were compared with the theoretical calculations. The basis set that gives the most accurate result with the experimental values, the modified Stuttgart basis set was chosen to be used in the next calculations.
For the theoretical chemical calculations of the interaction of SiO2-B2O3-ZnO mixed glass with Eu3+ and Tb3+, individual ZnO, B2O3 and SiO2 cluster structures were calculated, their interactions with lanthanide ions were computed. The ionization potentials required for electron transmission, electron affinities, chemical hardness, electron hole reorganization energy and homo-lumo gaps were calculated. Time dependent TD-DFT method and TPSSh hybrid functional were used in the calculation of emission spectra of lanthanide doped clusters. The calculated emission wavelengths were found to be in agreement with the experimental values.
After the glass layer absorbs the UV light, it will glow in the visible region. This wavelength of radiation will be directed to the edge of the window plastic where the thin strips of PV solar cells in the transparent solar panel convert it into electricity. Thus, electricity will be produced from the luminous glass alone. From the outputs of this thesis, it is predicted that the proposed lanthanide doped glass mechanism can be integrated into each solar cell, and will contribute an additional efficiency as hybrid solar cells.
