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Tham khảo tài liệu 'solar cells dye sensitized devices part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 142 Solar Cells - Dye-Sensitized Devices The calculated optical absorption spectra are shown in Fig. 8. We found that the absorption spectra will be red shifted by prolonging the oligoene backbone compare the green and red lines and inserting cyclohexadiene moiety compare the lines in the same colour . Attaching benzene rings to the amide nitrogen could enhance the absorption intensity a little but barely changes the position of maximum absorption compare blue and green lines . On the other hand inserting cyclohexadiene group could modify the spectra significantly both in peak positions and intensity compare the lines in Fig. 8 in the same colour . This would make dyes with cyclohexadiene group attractive candidates for future development of DSSC devices especially for high extinction long wavelength light absorption. We analyse further the electronic energy level calculated using B3LYP 6-31G d and the first excitation energy from CỮB97X 6-31G d Table 1 . It is known that the solvent effects will lower dye absorption energy by 0.1-0.3 eV Pastore et al. 2010 therefore experimental values quoted in Table 2 which are measured in solution would have been corrected by 0.1- Fig. 7. Chemical structure of model dyes. The left column from up to bottom depicts Y-l Y-2 Y-3 and the right column shows Y-lben Y-lben2 Y-2ben Y-3ben. Fig. 8. Calculated optical absorption spectra of the model dyes. Dye Sensitized Solar Cells Principles and New Design 143 0.3 eV this leads to a better agreement with the results from LC-TDDFT for dyes in vacuum. For Y-l dye the LC seems not necessary maybe due to its short length. Intuitively the energy levels of the whole dye molecule are modified by the electric field introduced by the presence of chemical groups at the acceptor end. They would change according to the electronegativity of these chemical groups. The higher negativity the lower the LUMO level the smaller the energy gap would be. Our results proved this simple rule by showing that .
