Theoretical Investigations On The Electronic And Related Properties Of Phorphyrin Dye Sensitizers And PC₇₁BM

Dye-sensitized solar cells (DSSCs) as a new type of semiconductor photoelectrochemical cells, have attracted a wide attention of many global research scholars because of easy fabrication, low cost, and relatively better thermal stability. However, the photoelectric conversion efficiency (PCE) of the dye-sensitizer solar cells is still not high enough, so the central interest of scientific research still focuses on how to improve the PCE. It is shown that the performance of the dye sensitizer has a significant influence for improving the PCE of cells. Physical and photoelectrochemical properties of seven porphyrin sensitizer YD2, YD2-o-C8, YD20, YD21, YD22,2Flu-ZnP-COOH and2Flu-ZnP-CN-COOH were calculated via density functional theory (DFT) and time-dependent density functional theory (TDDFT) including geometries structure, electronic structure, absorption spectra, etc. The calculated data indicates that, compared with the performance of YD2, the better performance of YD2-o-C8results from the more excited states with effective charge transfer excitation character and the larger free energy change for electron injection so as to contributing to the formation of the photocurrent; on the methodological view, HSE06functional is suitable for describing excitation properties of porphyrin dyes where the pull group is carboxyl acid group, while the CAM-B3LYP functional is suitable for porphyrin dyes with cyanoacrylic acid as pull group; electron withdrawing ability of electron acceptor cyanoacrylic acid is stronger than carboxylic acid; the introduction of different acceptors can modify the semiconductor conduction band edge to adjust the open circuit voltage of DSSCs and so on.In recent decades, organic solar cells have also more and more attention due to their potential for low-cost, light weight, more flexible and larger production area. Especially, as an electron acceptor material, fullerene derivatives are made into stacked organic solar cell device which exhibit a high photoelectric conversion efficiency. The properties of the organic solar cells accepter material PC71BM two isomers, including of the geometries structure, electronic structure, electronic absorption spectra, infrared and Raman spectra and polarizabilities and hyperpolarizabilities are calculated using DFT and TDDFT and the results are analyzed, too. Founding that the vibrational modes of [6,6]PC71BM and [5,6]PC71BM at IR and Raman peaks are quite similar, and also very similar to that of PC61BM; The calculated exciton binding energy of [6,6]PC71BM is smaller than that of [5,6]PC71BM and it is favorable for exciton dissociation in heterojunction; the larger isotropic polarizability of PC71BM indicates PC71BM has stronger response of external field and nonlinear optical properties than that of PC61BM.